controlling the physical properties of organic ... · controlling the physical properties of...
TRANSCRIPT
Controlling the Physical Properties of Organic Semiconductors through Siloxane Chemistry and other
Organic Electronic Materials
by
Brett A. Kamino
A thesis submitted in conformity with the requirements for the degree of Doctor of Philosophy
Chemical Engineering and Applied Chemistry University of Toronto
© Copyright by Brett A. Kamino 2013
ii
Controlling the Physical Properties of Organic Semiconductors
through Siloxane Chemistry and other Organic Electronic
Materials
Brett A. Kamino
Doctor of Philosophy
Department of Chemical Engineering and Applied Chemistry University of Toronto
2013
Abstract
Triarylamine type materials with vastly altered physical properties are synthesized by
hybridizing organic semiconducting structures with silicone and siloxane groups. By altering the
silicon content of these materials, we can tune their physical composition from free flowing
liquids, to amorphous glasses, to cross-linked films. Much of this modification is enabled by the
unique use of a metal-free Si-H activation chemistry; the Piers-Rubinsztajn reaction. This
chemistry is demonstrated to be a general and rapid way to build up hybrid semiconducting
structures. Key to the utility of these materials in electronic devices, it is shown that
hybridization with silicon groups has a negligible effect on the useful electrochemical properties
of the base materials. Building on this, it is shown that charge carrier mobility through a
prototypical liquid organic semiconductor is similar to the base materials and transport is
described by existing dispersive transport theories. Finally, two side projects in the area of
organic electronics are discussed. New phthalonitrile based fluorophores are characterized and
their utility as deep-blue emitting dopants in organic light emitting diodes is demonstrated. These
same π-extended phthalonitriles can also be used as precursors to new red-shifted BsubPcs which
display exceptional electrochemical stability and tuning.
iii
Acknowledgments
I would like to thank all of my friends and family for their constant support and understanding as
I embarked on a longer than planned educational adventure. In particular, I need to thank my
Mother and Father for pretending to understand my project and legitimately being proud of my
accomplishments. I thank all of my friends outside of grad school and especially Lana for
helping to keep me sane throughout the years.
I would also like to thank all of the members of the Bender lab past and present for being such a
warm group of friends and colleagues. The friendly atmosphere maintained in the laboratory and
at the pub after the laboratory has made my PhD experience all the better and easier to deal with
over the years. As well, I’d like to thank everyone for providing a patient ear to any frustrations
I’ve had over the years.
Lastly, I’d like thank Professor Bender for originally taking me into the group and giving me a
chance to earn my PhD. You’ve been a patient supervisor and have enabled to have a great deal
of freedom to explore my own scientific path. Finally, I’d to thank you for putting up with my
constant rebellion and for your belief in me.
iv
Table of Contents
Acknowledgments .......................................................................................................................... iii
Table of Contents ........................................................................................................................... iv
List of Tables ................................................................................................................................. ix
List of Figures and Schemes ........................................................................................................... x
Chapter 1: Introduction ............................................................................................................. 1
1.1 Organic Electronics Background ........................................................................................ 1
1.2 Thesis Overview ................................................................................................................. 3
1.3 Thesis Statement ................................................................................................................. 4
1.4 Background on Triarylamines ............................................................................................. 4
1.5 Engineering the Physical Properties of Organic Semiconductors ...................................... 6
1.6 References ........................................................................................................................... 9
Chapter 2: The Use of Siloxanes, Silsesquioxanes, and Silicones in Organic Semiconducting Materials ........................................................................................................ 11
2.1 Executive Summary .......................................................................................................... 11
2.2 Statement of Contributions ............................................................................................... 11
2.3 Paper ................................................................................................................................. 11
2.3.1 Abstract ................................................................................................................. 11
2.3.2 Introduction ........................................................................................................... 12
2.3.3 Chemistries for Silicone and Siloxane Incorporation ........................................... 14
2.3.4 Examples of Hybrid Materials .............................................................................. 18
2.3.5 Conclusions and Outlook ...................................................................................... 32
2.4 References ......................................................................................................................... 32
Chapter 3: Effect of Triarylamine Structure on the Photoinduced Electron Transfer to Boron Subphthalocyanine ........................................................................................................ 37
3.1 Executive Summary .......................................................................................................... 37
v
3.2 Statement of Contributions ............................................................................................... 38
3.3 Paper ................................................................................................................................. 38
3.3.1 Abstract ................................................................................................................. 38
3.3.2 Introduction ........................................................................................................... 38
3.3.3 Results and Discussion ......................................................................................... 40
3.3.4 Conclusions ........................................................................................................... 50
3.3.5 References ............................................................................................................. 50
3.3.6 51
Chapter 4: Controlling the Physical and Electrochemical Properties of Arylamines Through the Use of Simple Silyl Ethers: Liquid, Waxy and Glassy Arylamines .................... 52
4.1 Executive Summary .......................................................................................................... 52
4.2 Statement of Contributions ............................................................................................... 53
4.3 Paper ................................................................................................................................. 53
4.3.1 Abstract ................................................................................................................. 53
4.3.2 Introduction ........................................................................................................... 53
4.3.3 Results and Discussion ......................................................................................... 55
4.3.4 Conclusions ........................................................................................................... 65
4.3.5 References ............................................................................................................. 66
Chapter 5: Siloxane-Triarylamine Hybrids: Discrete Room Temperature Liquid Triarylamines via the Piers-Rubinsztajn Reaction ................................................................... 68
5.1 Executive Summary .......................................................................................................... 68
5.2 Statement of Contributions ............................................................................................... 68
5.3 Paper ................................................................................................................................. 69
5.3.1 Abstract ................................................................................................................. 69
5.3.2 Body ...................................................................................................................... 69
5.3.3 References ............................................................................................................. 74
vi
Chapter 6: Liquid Triarylamines: The Scope and Limitations of Piers-Rubsinsztajn Conditions for Obtaining Triarylamine-Siloxane Hybrid Materials ........................................ 76
6.1 Executive Summary .......................................................................................................... 76
6.2 Statement of Contributions ............................................................................................... 76
6.3 Paper ................................................................................................................................. 77
6.3.1 Abstract ................................................................................................................. 77
6.3.2 Introduction ........................................................................................................... 77
6.3.3 Results and Discussion ......................................................................................... 79
6.3.4 Conclusions ........................................................................................................... 91
6.3.5 References ............................................................................................................. 93
Chapter 7: Hole Mobility of a Liquid Organic Semiconductor .............................................. 95
7.1 Executive Summary .......................................................................................................... 95
7.2 Statement of Contributions ............................................................................................... 96
7.3 Paper ................................................................................................................................. 96
7.3.1 Abstract ................................................................................................................. 96
7.3.2 Body ...................................................................................................................... 96
7.3.3 References ........................................................................................................... 104
Chapter 8: Crosslinked Triarylamine-Siloxane Films using Piers-Rubinsztajn Chemistry . 106
8.1 Executive Summary ........................................................................................................ 106
8.2 Statement of Contributions ............................................................................................. 106
8.3 Paper Draft ...................................................................................................................... 107
8.3.1 Abstract ............................................................................................................... 107
8.3.2 Introduction ......................................................................................................... 107
8.3.3 Results and Discussion ....................................................................................... 109
8.3.4 Conclusions ......................................................................................................... 116
8.3.5 References ........................................................................................................... 117
vii
Personal Interest Projects 1: Design of Deep-Blue Emitting Materials for OLEDs ................... 120
Chapter 9: ............................................................................................................................... 120
9.4 Executive Summary ........................................................................................................ 120
9.5 Statement of Contributions ............................................................................................. 120
9.6 Paper ............................................................................................................................... 121
9.6.1 Abstract ............................................................................................................... 121
9.6.2 Introduction ......................................................................................................... 121
9.6.3 Results and Discussion ....................................................................................... 122
9.6.4 Conclusions ......................................................................................................... 131
9.7 References ....................................................................................................................... 131
Chapter 10: Personal Interest Projects 2: Colour Tuning Boron Subphthalocyanine ............ 134
10.1 Executive Summary ........................................................................................................ 134
10.2 Statement of Contributions ............................................................................................. 134
10.3 Paper ............................................................................................................................... 134
10.3.1 Body .................................................................................................................... 134
10.3.2 References ........................................................................................................... 144
Chapter 11: Concluding Remarks and Future Work ................................................................... 147
Chapter 11: ............................................................................................................................. 147
11.1 Summary ......................................................................................................................... 147
11.2 Future Directions ............................................................................................................ 150
11.3 References ....................................................................................................................... 152
Appendices .................................................................................................................................. 153
Chapter 12: ............................................................................................................................. 153
12.1 Additional Information for Chapter 3 ............................................................................. 153
12.1.1 Experimental Information ................................................................................... 153
12.1.2 Supplemental Information of Merit .................................................................... 157
viii
12.2 Additional Information for Chapter 4 ............................................................................. 160
12.2.1 Experimental Information ................................................................................... 160
12.3 Additional Information for Chapter 5 ............................................................................. 168
12.3.1 Experimental Information ................................................................................... 168
12.4 Additional Information for Chapter 6 ............................................................................. 169
12.4.1 Experimental Information ................................................................................... 169
12.4.2 Supplemental Information of Merit .................................................................... 184
12.5 Additional Information for Chapter 7 ............................................................................. 189
12.5.1 Experimental Information ................................................................................... 189
12.5.2 Supplemental Information for Chapter 7 ............................................................ 191
12.6 Additional Information for Chapter 8 ............................................................................. 194
12.7 Additional Information for Chapter 10 ........................................................................... 197
12.7.1 11.7.1 Experimental Information ........................................................................ 197
12.8 Appendices References for Chapter 10 ........................................................................... 199
12.8.1 General Information ............................................................................................ 199
12.8.2 Synthetic Details and Compounds Characterization ........................................... 200
12.8.3 NMR Study of Phthalonitrile 10-2 ...................................................................... 202
12.8.4 UV-Vis and PL Plots .......................................................................................... 205
12.9 DFT Calculated Molecular Orbitals ................................................................................ 209
12.10 Cyclic Voltammetry ............................................................................................ 214
ix
List of Tables
Table 3-1: Electrochemical oxidation potentials, fluorescence quenching efficiency, and free energy change upon photoinduced electron transfer reaction with 3,4-DMPhO-BsubPc for triarylamines (3-1a-i, 3-2a-c, 3-5b and 3-6b). 41
Table 4-1. Comparison of the physical and electrical properties of compounds 4-4a, 5 and 6 with previously reported analogous compounds. 54
Table 4-2. Comparison of the physical and electrical properties of compounds 4-4a-d including hydrolytic stability. 57
Table 4-3. Characterization data for multi-nitrogen centred triarylamine series, compounds 4-7, 4-8a-b, 4-9 and 4-11 (see Scheme 4-1 for chemical structures of TIPS and TBDPS). 61
Table 5-1: Thermal and electrochemical information for precursor triarylamine compounds 5-1a-c and their siloxane functionalized counterparts, 5-2a-c. 69
Table 6-1: DSC and CV results from silicone-hybridized triarylamines. 79
Table 8-1: Collected experimental information for different formulation conditions. 108
Table 9-1. Photophysical, electrochemical and thermal properties of compounds 9-1 and 9-2 120
Table 9-2. Performance of OLEDs incorporating 9-1 and 9-2 as dopants 127
Table 10-1: Calculated and experimentally determined properties of compounds F5BsubPc, 10-3a-b and 10-4a-c. 138
Figure 10-3: Cyclic voltammogram of BsubPc compound 10-4b in DCM with 0.1M tetrabutylammonium perchlorate and decamethylferrocene as an internal standard. 139
x
List of Figures and Schemes
Figure 1-1: Examples of common triarylamine materials utilized in organic electronics. Semiconducting…. 5 Figure 2-1: The molecular fragments of a silicone/siloxane organic electronic hybrid material (using a triarylamine as a representative example)… 11 Figure 2-2. Example of siloxane containing triarylamie applied in a xerographic… 22
Figure 2-3: Example of siloxane containing material used as an electron … 23
Figure 2-4. Structure of common silsesquioxane-T8 synthetic precursors. 24
Figure 2-5: Examples of several POSS-T8 derivatives functionalized with organic semiconducting groups. 25 Figure 3-1: Structures of 3,4-DMPhO-BsubPc and the triarylamines used in this study (containing either one (3-1a-i) or two nitrogen centers (3-2a-c)). 37 Figure 3-2: Size exclusions chromatograms of the triarylamine dendrimers (3-5a and 3-6a) and… 40 Figure 3-3: Solution electrochemistry of triarylamine dendrimers (3-5b, 3-6b) and a representative single triarylamine (3-1a). 43 Figure 3-4: Experimentally determined Stern-Volmer constants (K) plotted against half-wave oxidation potentials (E1/2,ox) of the triarylamine donor. 44 Figure 3-5: Experimentally determined Stern Volmer constant (K) plotted against the free energy change estimated by a modified Rehm-Weller equation (Eq. 3-2). 46 Figure 4-1 Two previously reported liquid arylamines. 50 Figure 6-1: Steady-state solution absorbance spectroscopy in toluene of a) compound 1 b) compound 6-4d with 0, 0.25, 0.5, and 1 equivalents of BCF. 85 Figure 7-1: Example photogenerated transients through (a) 2TIPS in a poly(styrene) matrix (9 um) and (b) neat 2TIPS (50 um) 94 Figure 7-2: Field dependent hole mobility as a function of temperature for 2TIPS in a (a) polystyrene matrix and (b) as a neat liquid. 96 Figure 7-3: Temperature dependence on hole mobility for 2TIPS doped in polystyrene (50 wt%) at 555 kV/cm and neat 2TIPS at 100 kV/cm. 99 Figure 8-1: IR spectra of QM4 and films F, E, and D (top to bottom). Film D prepared in a
matrix of KBr and the remainder studied by ATR. 109
Figure 8-2: (a) UV-Vis absorption (black) and photoluminescence spectra of
compound 4 in a THF solution (red) and a neat film (blue). (b) Photoluminescence
spectra of films A, D, and F on glass. 111
Figure 8-3: Electrochemistry with decamethylferrocene internal reference. 112
xi
Figure 9-1. Geometry optimized structure for (a) compound 9-1 (top) and (b) compound 2 (bottom) and their predicted HOMO and LUMO distributions. 119
Figure 9-2. Normalized absorption (black line) and emission spectra. 121
Figure 9-3a. (i) Electroluminescent spectra of compound 9-1 125
Figure 9-3b. (i) Electroluminescent spectra of compound 9-2 126
Figure 10-1: Thermal ellipsoid plot of (a) 10-3b·(THF)2 (CCDC deposition 910746) and (b)
10-4a·(CHCl3)2 (CCDC deposition 910747). 133
Figure 10-2: Normalized UV-Vis absorbance spectra of (a) F5BsubPc, 10-4a and 10-3b and (b) 10-4a-c. 136
Scheme 2-1: Summary of some common coupling techniques to join organic semiconductors with silicone/siloxane components 13 Scheme 2-2: Summary of synthetic strategies towards side-chain polymeric organic semiconductors. 16 Scheme 2-3. Cross section of an OLED device and examples of siloxane containing materials applied at either the ITO/hole transport layer interface… 19 Scheme 3-1: Synthetic pathway towards triarylamine dendrimers (3-5b and 3-6b). Conditions… 38 Scheme 4-1: Synthesis of triarylamines containing silyl ethers 53 Scheme 4-2 Synthesis of silyl ether containing arylamines with multiple nitrogen centres. 59 Scheme 5-1: Several synthetic transformations accessible by using the Piers-Rubinsztajn reaction. 66 Scheme 5-2: Synthesis of single nitrogen centered triarylamines 5-2a-c 68 Scheme 6-1: Synthesis of siloxane functionalized arylamines. 76 Scheme 6-2: Synthesis of spiro core triarylamine 6-9 81 Scheme 6-3: Synthesis of triarylamine 6-11 81 Scheme 6-2: Synthesis of siloxane functionalized carbazoles. 83 Scheme 8-1: Synthesis of an arylamine monomer for ring-opening under Piers-Rubinsztajn conditions. 106 Scheme 8-2: Reagents used to achieve functional cross-linked films using Piers-Rubinsztajn chemistry. 107 Scheme 9-1. Synthetic pathways towards phthalonitriles 9-1 and 9-2. 118
Scheme 10-1: Synthesis of π extended BsubPcs 10-3a-b and 10-4a-c and their precursor phthalonitriles. 132
xii
List of Abbreviations
OLED – organic Light Emitting Diode
OFET – organic Field-Effect Transistor
OPV – organic photovoltaic
DSC – differential Scanning Calorimetry
PDMS – poly(dimethylsiloxane)
BCF – tris(pentafluorophenyl)borane
PVK – poly(vinylcarbazole)
PSX – See Scheme 2-2
Tg – glass Transition Temperature
ITO – indium Tin Oxide
P3HT – poly(3-hexylthiophene)
PPV – Poly(phenylenevinylene)
POSS – silsesquioxane
AlQ3 - tris(8-hydroxyquinolinato)aluminium
PET – photoinduced electron transfer
BsubPc – boron subphthalocyanine
SEC – size exclusion chromatography
MM – hexamethyldisiloxane
TMEPA – tris(4-methoxyethoxyphenyl)amine
DSSC – dye sensitized solar cell
TIPS – triisopropylsilane
TBDMS – tert-butyldimethylsilane
THDMS – tert-hexyldimethylsilane
xiii
DPTBS – diphenyl-t-butylsilane
CV – cyclic voltammetry
MDHM – 1,1,1,3,5,5,5-heptamethyltrisiloxane
MMH – 1,1,3,3,3-heptamethyldisiloxane
HRMS – high resolution mass spectroscopy
LOS – liquid organic semiconductor
2TIPS - 3,4-dimethyl-N,N-bis(4-((triisopropylsilyl)oxy)phenyl)aninline (See Figure 7-11)
TPD - N,N`-diphenyl-N,N`-bis(3-methylphenyl)-(1,1`-biphenyl)-4,4`-diamine
TAPC - 1,1-bis(di-4-tolylaminophenyl)cyclohexane
QM4 - tetrakis(dimethylsilyl)orthosilicate
TGA - thermal gravimetric analysis
CIE - International Commission on Illumination
RGB – Red, Green, Blue
NTSC – National Television Standards Council
CBP - 4,4`-di(9-carbazolyl)-biphenyl
TPBi - 2,2`,2``-(1,3,5-benzinetriyl)tris(1-phenyl-1-H-benzimidazole
1
1
Chapter 1: Introduction
1.1 Organic Electronics Background
Organic electronic devices are a diverse group of technologies which use organic
semiconducting materials as a primary functional element. These devices include organic light
emitting diodes (OLEDs),1 organic field-effect transistors (OFETs),2 organic xerographic
photoreceptors,3 organic photovoltaics (OPVs),4 and many other devices.
All of these devices are based on semiconducting materials made up of organic small molecules,
oligomers, or polymers.5 This is in contrast to traditionally inorganic semiconductors based on
semimetals such as silicon. Much like silicon, organic semiconductors can be designed to
selectively move positive charge (holes) or negative charges (electrons). As well, they can be
designed to interact with light in a number of useful ways. These include the absorption of light
for exciton generation or quenching of excitons to generate light. By designing appropriate
materials and combining them with complementary materials in a full device structure,
remarkable electronic functions can be realized.
Such materials are gaining a great deal of attention due to several advantages inherent to using
organic semiconductors over their inorganic counterparts. Using organic semiconductors in
electronic devices has a number of potential advantages for widespread commercialization.
Among these advantages is the ability to process devices at substantially lower temperatures
using solution casting techniques. This has led to prototype roll-to-roll printing processes to be
investigated by a number of different groups.6 As well, organic semiconductors have
significantly lower purity requirements as compared to inorganic semiconductors in most cases.7
All of these aspects can lower the overall cost of processing organic electronic devices as
compared to those made with inorganic materials. This potentially lower cost of production has
produced a great deal of interest from both academic labs and industrial companies.
Beyond cost, organic material have another significant advantage over inorganic materials.
Through a diverse synthetic tool box and a healthy imagination, an almost infinite number of
organic materials can be produced to achieve an equally diverse set of electronic, optical, and
2
2
physical properties. This is something that is not possible with inorganic semiconductors which
are limited greatly by the real-estate of the periodic table.
Perhaps because of this immense potential for material optimization, a number of these device
types have already reached maturity and have achieved commercialization. The oldest example
of this is xerographic photoreceptors which have been the standard component in most
photocopying devices for well over a decade. More recently, we have seen the
commercialization of OLED based displays for televisions and personal electronics such as
smartphones.8 At the time of this writing, a number of industrial companies are in the process of
developing prototype devices for both OPVs9 and OFETs10 which are on the cusp of widespread
deployment.
Despite this success, a number of significant gaps remain in realizing the ultimate promise of
organic semiconductors for inexpensive and flexible electronic devices. Among these gaps,
many of them are on the processing side of organic semiconductors.
Organic electronics have long been hyped to allow for highly flexible and mechanically robust
devices build upon flexible plastic substrates. Indeed, this has been shown in a number of
prototype devices and even elastomeric devices which can be squished and stretched have been
demonstrated.11 While the benefits to this kind of device are obvious, the reality is that upon
repeated mechanical stresses, many of these devices rapidly degrade.12 This is due to a large
number of reasons including delamination and cracking of the brittle crystalline layers used in
these devices. While this drawback can be corrected by the careful design of specific device
architectures on extremely thin substrates,13 such substrates are not likely to be widely applicable
due to their poor mechanical properties. Given this interest in creating mechanically robust
flexible and stretchable devices, it seems peculiar that no one is interested in producing
semiconducting materials that are inherently flexible and stretchable.
Another unfulfilled goal of organic electronics has been the development of high-speed printing
processes such as roll-to-roll solution printing processes or ink-jet printing on an industrial scale.
These processes are envisioned to be similar to conventional printing where devices can be
rapidly constructed by printing successive layers of organic semiconductors from solution. This
goal would preclude expensive and slow vacuum processing and greatly help to bring down the
3
3
overall cost of organic electronic devices. Again, realization of this goal is prevented by the
current limitations of organic semiconductors and processing properties. Many organic
semiconductors are very poorly soluble in organic solvents and require the use of highly toxic
and environmentally damaging chlorinated solvents.14 This poses a number of downstream waste
issues as well as corrosion issues for a roll-to-roll printing apparatus. A second issue with this
goal is the difficulty of producing multi-layered devices. Most organic electronics devices
require successive layers of different materials for optimized function. However, printing a
second organic layer on top of a first layer will dissolve and mix the two layers together. This
can be avoided with orthogonal solvent processing,15 but few materials are amenable to this
strategy and it places severe restrictions on the materials chosen. To solve some of these
deficiencies, the development of high soluble materials with differential solubility would be
ideal.
I believe that further advances in the field of organic electronics will require the development of
organic semiconductors with highly tailored physical properties to help overcome some of
remaining challenges for organic electronics in the interest of industrial scale processibility.
However, inclusion of these specific physical properties must not occur at the cost of the
electronic and photonic properties that these materials make these materials useful. This
particular point posses a unique challenge in the design of new organic semiconducting materials
which will require new synthetic strategies and chemical processes.
1.2 Thesis Overview
This thesis is a compilation of published or to-be-submitted papers produced over the course of
my PhD thesis. Before each chapter, there is an executive summary detailing how the work in
that chapter relates to my thesis statement. After that, there is a statement of contributions
outlining what each of the authors on the paper worked on. For each chapter and publication, I
have done a large majority of the experimental work and the bulk of the writing of the paper
itself.
Included in this thesis are two chapters which are not related to my primary thesis statement
(Chapters 9 and 10). These chapters represent side projects that I initiated during my PhD thesis.
Both projects are related to the broader overall goals of the Bender Laboratory and the field of
4
4
Organic Electronics. Because these projects were completed during the course of my thesis, I
decided to include them as two ‘Personal Interest Projects’.
1.3 Thesis Statement
Selective incorporation of silicone and siloxane components into nitrogen-based hole
transporting compounds can be an effective tool to control the physical properties of organic
semiconductors. This can be done to produce materials which are morphologically stable glasses,
free-flowing liquids, and cross-linked films. For many of these materials, a novel use of the
Piers-Rubinsztajn reaction is demonstrated to be a facile and convenient method to hybridize
siloxane components with triarylamine components. We show that the introduction of siloxane
or silicone groups has a negligible effect on the useful electrochemical properties of the
materials. As well, we demonstrate that there is no significant difference in the charge carrier
mobility of a model liquid material as compared to the analogous solid compound.
1.4 Background on Triarylamines
Parts of this section have been taken and paraphrased from a paper published and discussed in
Chapter 3 (Brett A. Kamino, Graham E. Morse, Timothy P. Bender, 2011, Journal of Physical
Chemistry C, 115 (42), 20716-20723).
Throughout this thesis, we have chosen to focus our efforts on a single family of organic
semiconductors as a model group of compounds: triarylamines. Single and multi-nitrogen
centered triarylamines are an important class of functional materials in the area of organic
electronics. Owing to their well-behaved chemical and electrochemical oxidation, this class of
organic semiconductors represents one of the most frequently studied electron-donating materials
(hole-transporting materials) in the field.5 This makes them an attractive target for developing
synthetic methodologies to alter the physical properties of organic semiconductors. Several
popular examples of this motif are illustrated below in Figure 1-1.
5
5
N N N N
N N NN
OLED Materials
Xerography Materials
Figure 1-1: Examples of common triarylamine materials utilized in organic electronics
Beyond their basic ability to function as stable and reversible electron donors, the adoption and
study of these materials is aided by the demonstrated ability to modify their electronic and
physical properties over a wide range. Fine control over their oxidation potentials16 and access to
relatively stable polycations can be achieved by the appropriate use of electron-withdrawing/-
donating groups and by the construction of large molecules containing multiple conjugated
triarylamine centers. 1 †,17 Their physical properties can ranges between crystalline solids18 and
morphologically stable glasses.19 Because of their highly tunable properties, triarylamines have
become standard materials in some organic electronic devices such as xerographic
photoreceptors, light-emitting diodes, field effect transistors, bulk heterojunction solar cells,20
and solid-state dye-sensitized solar cells.21 As well, triarylamine moieties have been incorporated
into the molecular structure of light-absorbing oligomers, polymers,22 and photosensitizers.23
† We will use the term triarylamines to refer to all triarylamine structures regardless of number of nitrogen centers
and will include carbazole structures
6
6
1.5 Engineering the Physical Properties of Organic Semiconductors
One of the primary goals of this thesis was designing and synthesizing materials that were
liquids or elastomers at room temperature. We will define such compositions as soft materials.
Since soft organic semiconductors are not typical organic electronic materials, it is worth
exploring some of the design elements that needed to successfully design soft material
properties.
Because the design constraints for producing soft materials is quite different than that of typical
organic electronic materials, it is instructive to first discuss more typical materials as a point of
contrast. Surveying the organic electronic literature will reveal a vast array of different
compounds with different functions. These compounds can be roughly divided into two groups:
glass forming compounds and crystalline materials.
Crystalline materials are organic molecules whose solid state arrangement is highly ordered and
dominated by strong intermolecular interactions. These materials will typically form
polycrystalline films upon deposition from solution or vapour. Occasionally, careful processing
and favourable crystal packing can lead these kinds of materials to form single crystals.
However, this is often the exception. As well, the packing arrangement and degree of
crystallinity in these materials can have a profound effect on the final properties of the film and
performance of the completed device. Because of this, controlling intermolecular interactions is
key to optimizing the performance of many of these materials. In the field of organic electronics,
the most dominant intermolecular interaction is π-π stacking between adjacent molecules. This
should come as no surprise given that basically all organic electronic materials contained
extended-π systems in some form or another.
The second category of organic electronic materials, glass-forming compounds, has a very
different set of design principals compared to crystalline materials. Glass-forming compounds
are designed so that they form completely amorphous and homogeneous solid-state films upon
solution or vapour deposition. Such materials are ideal for applications where relatively low
charge-carrier mobilities are required and crystal defects can negatively affect device
performance. The primary application for such materials is for organic light-emitting diodes,
7
7
although xerographic photoreceptors often use amorphous materials as well. These materials
benefit greatly from a processing point of view because they are homogeneous. Therefore, there
are no issues with controlling crystal-grain size and orientation.
In designing these compounds, there are two specific design criteria which must be followed.
The first is designing a material without the ability to undergo strong intermolecular interactions
in the solid-state. And the second is designing a material with a very high glass transition
temperature to ensure morphological stability over time.
The first of these is critical to ensure that thin-film deposition will result in an amorphous
material instead of an ordered solid. As such, this instantly rules out compounds which are
highly planar and that contain strongly polar functionalities. Compounds with these elements
require significant structural modification in order to form amorphous films. Several examples
are discussed in chapter 2. Unfortunately, it is extremely difficult to design effective organic
electronic materials that do not contain many planar sections. Extended π-conjugation is one of
the defining characteristics of organic semiconductors and is often required to produce materials
with usable redox potentials. Because of this, the effective design of amorphous materials
requires a more insightful approach. These approaches all revolve around preventing π-π
stacking through increased steric hindrance and by lower overall symmetry of the molecule. Both
of these facets frequently involve producing molecules which extend into three dimensional-
spaces. Triarylamines are an excellent example of a material which can form glassy films. While
a simple triarylamine does not form glassy films well, larger derivatives such as those shown in
Figure 1-1 do. One of the key elements about triarylamines which help with forming amorphous
films is their propeller shape. Each phenyl ring around the nitrogen core is slightly twisted and
extends the molecule into three-dimensional space. Having several of these groups together on
the same molecule has been a successful strategy to produce glassy films.
The second design criterion for good glass forming compounds is to ensure a high glass
transition temperature for improved morphological stability. The glass transition temperature of a
material is defined as the temperature where a material transitions between being an amorphous
glass and a melt. This idea has strong roots in the polymer sciences and is most easily
characterized using differential scanning calorimetry (DSC). In a typical DSC experiment, the
glass transition temperature can be detected as a strong change in the slope of the heat flow. The
8
8
reason why the glass transition temperature is so critical for an amorphous material is because a
glassy-state is never the most thermodynamically stable state for a material. A crystalline-
compound takes advantage of intermolecular interactions which can energetically stabilize a
material in the solid-state. Therefore, glassy materials are only kinetically stable because they are
‘frozen’ in their particular arrangement. This energetic situation becomes a problem when glassy
semiconductors experience heating near or above their glass transition temperature. When this
happens, the material can rearrange to a more thermodynamically favourable crystalline state.
This will change the optoelectronic properties of the film. Therefore, a morphologically stable
glassy organic semiconductor requires a glass transition temperature that is much higher than the
typical operating temperatures of the intended devices. This is typically achieved by increasing
molecular size and by ensuring a very rigid structure. Larger molecules tend to have high glass
transition temperatures because of the increase thermal energy required for them to form a melt.
Rigid molecular structures similarly require more thermal energy to allow for molecular rotation.
For the design of soft organic semiconducting materials, we require materials with glass
transition temperatures below the operating and processing temperatures of the material but we
cannot allow the material to crystallize in the melt-state. These design criteria are quite difficult
and quite different from those of the previous sets of materials. However, from the previous
discussions we can discuss how one may achieve these properties. The first step is to prevent
crystallization of the molecule. This can be done by either designing a molecule with very weak
intermolecular interactions or by providing significant steric repulsion to prevent crystallization.
The second and, perhaps more important step, is to lower the glass transition temperature of the
material. This can be done by using very flexible elements in the molecule; molecular fragments
with very low conformational energy barriers.
9
9
1.6 References
1. a) Grimsdale, A.C.; Chan, K.L.; Martin, R.E.; Jokisz, P.G.; Holmes, A.B. Chem. Rev.
2009, 109, 987-1091., b)Xiao, L.; Chen, Z.; Qu, B.; Luo, J.; Kong, S.; Gong, Q.;
Kido, J. Adv. Mater. 2011, 23, 926-952.
2. Allard, S.; Forster, M.; Souharce, B.; Thiem, H.; Scherf, U. Angew. Chemie. Inter. Ed.
2008, 47, 4070-4098.
3. P. M. Borsenberger and D. S. Weiss, Organic Photoreceptors for Xerography, Marcel
Dekker Inc., New York, 1998.
4. Kippelen, B.; Brédas, J.-L. Energy Environ. Sci. 2009, 2, 251-261.
5. Shirota, Y.; Kageyama, H. Chem. Rev. 2007, 107, 953–1010.
6. Søndergaard, R.R.; Hösel, M.; Krebs, F.C. J. Polym. Sci. B.2013, 51 (1), 16-34.
7. Karl, N. Mol. Cryst. Liq. Cryst. 1989, 171, 157-177.
8. Rajeswaran, G.; Itoh, M.; Boroson, M.; Barry, S.; Hatwar, T.K.; Kahen, K.B.; Yoneda,
K.; Yokoyama, R.; Yamada, T.; Komiya, N.; Kanno, H.; Takahashi, H. SID
Symposium Digest of Technical Papers 2000, 31(1), 974-977.
9. Yue, D.; Khatav, P.; You, F.; Darling, S.B. Energy Environ. Sci. 2011, 4, 1434.
10. Bobbert, P.A.; Sharma, A.; Mathijssen, S.G.J.; Kemerink, M.; de Leeuw, D.M. Adv.
Mater. 2012, 24, 1146-1158.
11. Lipomi, D.J.; Chong, H.; Vosgueritchian, M.; Mei, J.; Bao, Z. Sol. Energy Mater. Sol.
Cells, 2012, 107, 355-365.
12. Sokolov, A.N.; Cao, Y.; Johnson, O.B.; Bao, Z. Adv. Mater. 2012, 22, 175-183.
13. Yi, H.T.; Payne, M.M.; Anthony, J.E.; Podzorov, V. Nature Comm. 2013, 3, ASAP.,
Kaltenbrunner, M.; White, M.S.; Glowacki, E.D.; Sekitani, T.; Someya, T.; Sariciftci,
N.S.; Bauer, S. Nat. Comm. 2012, 3, 770
10
10
14. Galagan, Y.; Vries, I.G.; Langen, A.P.; Andriessen, R.; Verhees, W.J.H.; Veenstra, S.C.;
Kroon, J.M. Chemical Engineering and Processing 2011, 50, 454-461.
15. Ahmed, E.; Earmme, T.; Jenekhe, S.A. Adv. Func. Mater. 2011, 21, 3889-3899. Tung,
C.V.; Kim, J.; Cote, L.J.; Huang, J. J. Am. Chem. Soc. 2011, 133, 9262-9265.
16. (a) Bender, T. P.; Graham, J. F.; Duff, J. M. Chem. Mater. 2001, 13, 4105–4111. (b)
Amthor, S.; Noller, B.; Lambert, C. Chem. Phys. 2005, 316, 141–152.
17. Thelakkat, M. Macromol. Mater. Eng. 2002, 287, 442–461.
18. Song, Y.; Di, C.; Yang, X.; Li, S.; Xu, W.; Liu, Y.; Yang, L.; Shuai, Z.; Zhang, D.; Zhu,
D. J. Am. Chem. Soc. 2006, 128, 15940–15941.
19. Gagnon, E.; Maris, T.; Wuest, J. D. Org. Lett. 2010, 12, 404–407.
20. Sommer, M.; Lindner, S. M.; Thelakkat Adv. Funct. Mater. 2007, 17, 1493–1500.
21. Li, B.; Wang, L.; Kang, B.; Wang, P.; Qiu, Y. Sol. Energ. Mater. Sol. Cells 2006, 90 (5),
549–573.
22. Brabec, C.; Dyakonov, V.; Sherf, U. Organic Photovoltaics: Materials, Device Physics,
and Manufacturing Technologies; Wiley Verlag GmbH: Weinheim, 2008.
23. Ning, Z.; Tian, H. Chem. Commun. 2009, 5484–5495.
11
11
Chapter 2: The Use of Siloxanes, Silsesquioxanes, and Silicones in Organic Semiconducting Materials
2.1 Executive Summary
This article is a tutorial review that was submitted to Chemical Society Reviews. This paper
covers how non-conductive silicon elements can be used to optimize the physical properties of
organic semiconductors. More importantly, this also places the work performed in my thesis
within context of the field.
This paper covers how silicone and siloxane chemistry has been previously used in the literature
with organic semiconductors. These examples range from small molecules, to polymers, to
cross-linked films. I believe that these examples help to convey the power of silicon chemistry to
control the physical properties of organic semiconducting materials. As a side benefit, it acts as a
concise and topical literature review on the integration of various silicon chemistries into organic
semiconducting materials.
2.2 Statement of Contributions
The idea, content, organization, and writing of this paper were entirely done by me with writing
input from Prof. Bender as corresponding author.
2.3 Paper
2.3.1 Abstract
Optimization of the physical and electronic properties of organic semiconductors is a key step in
improving the performance of organic light emitting diodes, organic photovoltaics, organic field
effect transistors, and other electronic devices. Separate tuning of the physical and electronic
properties of these organic semiconductors can be achieved by the hybridization of organo-
silicon structures (silicones, siloxanes, silsesquioxanes) with organic semiconductors. Common
chemical means to achieve this hybridization are summarized while a large range of literature
examples are covered to demonstrate the range and flexibility of this synthetic strategy.
12
12
2.3.2 Introduction
The study and application of organic semiconducting materials has emerged as an area of intense
interest in both the academic and industrial communities. The proven utility of organic
semiconducting materials in light emitting diodes (OLED),1,2 photovoltaics (OPV),3,4
xerography,5 field effect transistors (OFET),6 and many other device types,7 has prompted
significant study into both the discovery of new materials (novel compositions) and optimizing
known classes of materials and their chemical structures. To do this, chemists and engineers have
relied on the ability to modify the electronic and physical properties of these semiconducting
materials through rational chemical design of the semiconductors’ structure.8 Broadly stated,
changes to a chemical structure can be used to tune the electronic properties of materials in order
to alter its energy levels, interactions with light, chemical stability and other properties. These
changes can be subtle, such as an addition of a single electron withdrawing or electron donating
group. Or, they can be more substantial like dimerization or extension of a π conjugated system.
Chemical modifications can also alter the physical properties of these materials, properties which
impact the processibility of the material as well as its performance. These properties can be tuned
to improve such characteristics as device processing conditions, thin film formation, solubility,
and intermolecular interactions. Absolute control over both the electronic and physical properties
is critical when designing organic semiconducting structures. And, care must be taken not only to
how the material acts on its own, but how it acts when combined with other complementary
materials in a complete device.
While significant changes can be made to semiconductor properties through molecular
engineering, trying to tune certain properties while not affecting others can be quite difficult. For
example, one may want to increase conjugation length in a planar organic semiconductor to
improve charge transport. Such changes can result in a decrease in solubility and changes in the
intermolecular interactions in the solid state. Indeed, both the physical and electronic properties
of many organic semiconductors are interrelated and chemical modifications are rarely entirely
selective to one set of properties or the other. Therefore, it is of immense utility to be able to
engineer materials with independent control over both the physical and electronic properties.
One method which has been successful in decoupling physical and electronic properties has been
the incorporation of siloxanes and silicones into organic semiconductor molecular structures. It is
13
13
this method which is the focus of this tutorial review.
Silicones and siloxanes are a ubiquitous class of materials in modern society and are found in
many different applications including anti-foaming agents, lubricants, cosmetics, and coatings.9
This broad group of materials are generally considered quite thermally stable, electronically inert
and rather non-toxic. Most industrial applications use poly(dimethylsiloxane) (PDMS) or cross-
linked varients of this same polymer. But, silicon chemistry is an extremely diverse subject
touching many aspects of biology, organic synthesis, and materials chemistry. An authoritative
book on silicon in many different roles may be referenced for more information.10 Much of
silicon chemistry is dominated by its bonding with oxygen atoms and different classes of silicon
containing materials can be defined by their bonding with this element. Therefore, from a
nomenclature standpoint we will consider all silicon compositions with a basic formula of
[R2SiO2]n to be a siloxane or silicone. Furthermore, we will roughly define siloxanes as small
molecule fragments with this empirical formula and silicones to be their macromolecular
equivalents. Silicon compounds with the empirical formula RSiO2/3 are known as
silsesquioxanes. These cage like structures share some properties and common chemistry with
siloxanes and silicones and thus will be included in this tutorial. As well, silicon can take on
other empirical formulae resulting in materials that are electronically active. Examples include,
silicon atoms included in conjugated aromatic structures such as siloles and silica nano-crystals
(with an formula of [SiO2]n). While certainly interesting, these additional classes of materials
will not be considered within the scope of siloxanes and silicones and this tutorial.
At first glance, the incorporation of silicon(e) into an organic electronic material is a rather
curious strategy. Siloxanes and silicones are known for their high dielectric constants and are
considered to be quite electronically inert. However, it is this exact property that allows
independent tuning of physical and electronic properties in these hybrid materials. Because
added siloxane functionalities have a small impact on the electronic properties of a
semiconductor, their function can purely be to engineer the physical attributes of the final
material. This idea is illustrated in Figure 2-1.
In this tutorial review, the use of silicones and siloxanes in organic electronic materials will be
14
14
discussed and explored. Specifically, the methods of incorporating silicones and siloxanes into
the chemical structure of existing classes of organic semiconducting materials will be briefly
covered. This will include popular and efficient coupling strategies used to join silicon
containing precursor materials to organic semiconductors as well as some fundamental
considerations into their use. Examples of hybrid materials will be discussed in detail with a
focus on the specific impact that silicone and siloxane incorporation has on the final physical and
electronic properties of the materials. For the purpose of this article, these materials are divided
into several broad groups based on the nature of materials and include: discrete small molecules
and dendritic structures, polymers, and cross-linked films. This tutorial review is written to serve
as a tour into how traditional silicon chemistry can be integrated into the area of organic
semiconducting materials to produce new and exciting forms of applied matter and materials.
Figure 2-1: The molecular fragments of a silicone/siloxane organic electronic hybrid material (using a triarylamine as a representative example) and the relative effects of each fragment on
the overall properties of the hybrid.
2.3.3 Chemistries for Silicone and Siloxane Incorporation
While there may be many methods for chemically bonding siloxane and organic semiconductor
functionalities, several considerations must be made before a synthetic pathway is chosen. The
first must be the availability of different siloxane and silicone precursors and their associated
chemical functionalities. The availability of these reagents greatly reflects the industrial uses of
these chemicals. Because of this, certain silicon functionalities may be acquired quite
inexpensively while others inexplicably difficult or impossible to find. The second consideration
15
15
is the functionality present in the organic semiconducting fragment. In particular, some thought
must be made into how the organic semiconducting group is to be coupled with the silicon
containing fragment. Because most organic semiconducting structures have more synthetic
variability than do silicone or siloxane precursors, this half of the coupling strategy is often more
flexible. Below we outline several coupling strategies; each requiring a different, yet commonly
encountered functional group to be present on each of the organic semiconducting segment and
silicon containing fragment.
The last consideration and the one that limits the number of potential reagents/reaction
conditions used is the potential chemical instability of siloxanes and silicones. While stable to
many conditions, siloxane and silicone structures can often be hydrolytically unstable at any pH
other than neutral. Reaction or workup conditions involving acidic or basic aqueous conditions
will often result in hydrolysis ultimately leading to redistribution and/or metathesis of the
siloxane component.10, 11 This will lead to a loss of discrete structure and the generation of poorly
defined silicone oligomers in most cases, a problem which may be of some concern depending
on the needs of the final material. As will be seen in the examples to come, these issues can be
avoided by simply choosing reaction and purification conditions appropriately.
Finally, while other ways to form silicon/siloxane bonds or couple silicones to carbon do clearly
exist, we have chosen to focus on three primary reactions for this tutorial based on their
generality and frequency of use in the literature.
16
16
Scheme 2-1: Summary of some common coupling techniques to join organic semiconductors with silicone/siloxane components.
2.3.3.1 Hydrosilylation
Hydrosilylation is one of the most common methods for creating hybrid materials from silicones
and perhaps one of the most general. Hydrosilylation is the addition of a silane (Si-H) to an
unsaturated carbon-carbon bond (alkene or alkyne) resulting in the formation of a carbon-silicon
bond typically following anti-Markovnikov addition (Scheme 2-1).12 This transformation is most
often mediated by platinum-based catalysts, although free-radical initiated methods as well as
rhodium, nickel, and other transition metals can be utilized.10 To effect this reaction, the two
most common platinum catalysts are either Pt0 species such as Karstedt’s catalyst (Scheme 2-1)13
or H2PtCl6, a PtIV species known as Speier’s Catalyst (Scheme 2-1).14 For practically all of the
examples discussed below, these catalysts are sufficiently active to achieve clean reactions while
also being commercially available. For most systems containing few functional groups (most
organic semiconducting species), platinum catalysts are effective and a good starting point for
experimentation. Systems which contain strong coordinating functionalities such as amines or
phosphines are not compatible with this chemistry due to competitive binding of the platinum
catalyst. Many other common silicone/siloxane functionalities are compatible with this chemistry
17
17
including chloro-silanes and alkoxy-silanes which can be further reacted in subsequent processes
under orthogonal conditions. For the unsaturated carbon-carbon bond, vinyl or allyl groups are
most often used and easily incorporated into many organic semiconducting structures usually by
using suitably functionalized precursor materials during synthesis.
2.3.3.2 Piers-Rubinsztajn Reaction
The Piers-Rubinsztajn reaction15,16 is a relatively new process to join siloxane/silicone
functionalities with organic molecules, including organic semiconducting materials.17-20 This
reaction takes place between a silane and an aryl or alkyl hydroxyl or alkoxy group (Scheme 2-1)
and is catalysed by tris(pentafluorophenyl)borane (B(C6F5)3 or simply BCF), a strong and water
tolerant Lewis acid. Like hydrosilylation, the Piers-Rubinsztajn reaction proceeds with low
catalyst loadings and there are no significant by-products beyond gaseous hydrocarbons which
are easily dealt with on a laboratory scale. Because Piers-Rubinsztajn reactions can result in the
rapid generation of flammable gases (H2, CH4, etc.), some degree of caution must be exercised
when dealing with this process. Despite this minor downside, the reaction is compatible with a
variety of different silanes including small molecules18-20 and polymers.17 It should be noted that
alkoxy-silanes will also react under these conditions.21 Many other chemical functionalities are
tolerated so long as they cannot coordinate with the highly Lewis acidic BCF catalyst.22
Molecules with even moderate donor capacity (carbonyls for example) can either poison the
catalyst or undergo unwanted side-reactions such as hydrosilylation of the carbonyl group.23
While the Piers-Rubinsztajn reaction may be less tolerant of other functional groups than
hydrosilylation, it has the added benefit of using simple coupling partners such as hydroxyl or
alkoxy functionalities. These functionalities can easily be incorporated into the chemical
structures of some organic semiconductors. As well, unlike the functional groups required for
hydrosilylation, these functionalities are not potentially heat sensitive. Given these two points,
Piers-Rubinsztajn conditions may result in a more straightforward synthetic pathway in certain
situations to silicone containing organic electronic materials.
2.3.3.3 Mizoroki-Heck Reaction
The Mizoroki-Heck reaction is a palladium catalysed cross-coupling reaction between an
unsaturated carbon-carbon bond (typically an alkene) and an aryl halide resulting in the
formation of a carbon-carbon single bond (Scheme 2-1).24,25 This reaction is most often catalysed
18
18
by palladium metal ligated by an organophosphine in the presence of stoichiometric amounts of a
weak base; although many variations exist.26 Because of the widespread use of hydrosilylation
chemistry in industry, many vinyl-silicone functionalized starting materials exist. These vinyl
groups can be used as reagents in the Mizoroki-Heck reaction making them convenient starting
materials. Similar to hydrosilylation, this reaction has a wide scope and is compatible with many
organic functional groups. As well, it has the advantage of requiring an aryl-halide functionality
for reaction. Halides can be easily introduced in many chemical structures through the use of
easily handled halogenating reagents such as N-halosuccinimides. Aryl-halides are also more
heat stable than many vinyl-functionalities used in hydrosilylation conditions thus making
purification of organic electronic materials containing halides more desirable.
2.3.4 Examples of Hybrid Materials
2.3.4.1 Polymeric Materials
Polymeric materials represent the first disclosed examples of siloxane-organic semiconductor
hybrid structures. The concept was first shown by Strohriegl in a report from 1986.27 Drawing
from interest in poly(vinylcarbazole) (PVK) as a photoconductor for xerographic photoreceptors
and a precursor to conductive polymers, Strohriegl and co-workers synthesized a side-chain
carbazole polymer with a siloxane main chain as a structural analogue to PVK. This was
achieved by reacting poly(methylhydrosiloxane) with an N-vinyl functionalized carbazole under
standard hydrosilylation conditions, the product of which was given the general term PSX
(Scheme 2-2). Over the course of this work and several follow up publications,28-30 Strohriegl
and co-workers demonstrated that this is a facile method to producing siloxane-organic
semiconductor hybrid materials.
19
19
Scheme 2-2: Summary of synthetic strategies towards side-chain polymeric organic semiconductors.
The PSX class of materials was found to have significantly lower glass transition temperatures
(Tg) than PVK (which generally has a Tg > 200 °C). This is expected given the greater
conformational freedom found in poly(siloxane)s as compared to typical polyalkanes. This
increase in conformational freedom along the main polymer chain also results in a complete
absence of carbazole excimer formation under photoluminescence. In contrast, significant
excimer formation is observed in PVK thin solid films and in solution. This had already been
studied in detail for PVK and is understood to occur due to interactions between neighbouring
carbazole pendant units.31 The absence of these interactions in the analogous poly(siloxane)
hybrid materials is a good example of how siloxane hybridization is capable of controlling
intermolecular interactions between organic semiconducting moieties. Finally, these materials
were found to be effective photoconductors as shown by a series of time-of-flight mobility
experiments.30 Comparing a series of different polymers with varying side chain lengths, it was
found that these polymers have comparable charge mobility and photogeneration efficiencies to
PVK. Considering the already proven utility of PVK for organic electronic devices at the time,
these initial results showed that siloxane hybrid materials also had the potential to be
successfully used in such devices.
2-2 2-3
2-1
(PSX)
20
20
Most of the hybrid macromolecular materials share a common synthetic pathway to post-
polymerization functionalization, namely the utilization of hydrosilylation chemistry. However,
an alternate pathway to similar materials has recently been demonstrated by our laboratory
(Scheme 2-2, Compound 2-2).17 This approach relies on Piers-Rubinsztajn conditions to react an
aryl methoxy functionalized triarylamine with poly(methylhydro-co-methylphenyl)siloxane. This
alternate synthetic methodology has the benefit of avoiding the need for reactive allyl or vinyl
groups to be present on the triarylamine units. Instead it utilizes aryl-methyl ether groups as
reaction partners (Scheme 2-2) which are chemically stable prior to Piers-Rubinsztajn conditions
and easily incorporated into triarylamines. As well, it does not require expensive platinum based
catalysts and alleviates concerns about their subsequent removal from the final product.
Of all the potential applications of these materials, the area of photorefractive composites has
been impacted the most by the availability of siloxane hybrid polymers. Devices based on these
composites respond to incident light by changing their refractive index. Because of these
properties, photorefractive devices based on organic polymers are of interest for potential
application in optical data storage media and optical security systems.32 Traditional polymeric
systems based on blends of PVK as a photosensitizer and non-linear optical chromophores show
good initial performance but suffer from several drawbacks. Crystalline components in these
blends are not morphologically stable and many blends suffer from crystallization and phase
separation over time. The other serious problem is due to the orientational enhancement effect in
photorefractive polymers.33 This effect is the enhancement of the photorefractive properties with
increasing orientational mobility of the photorefractive components within the blend. Because of
this, optimal performance for these devices is achieved in blends with a great deal of
conformational freedom and a low glass transition temperature (Tg). This requirement
exacerbates the issues of morphological instability, an issue which can be partially eliminated by
the use of additional plasticizers. But, these plasticizers have the additional downside of diluting
the photorefractive effect.
Because of their inherently low Tg and amorphous nature, siloxane modified polymeric host
materials have been shown to be a solution to the aforementioned issues when acting as hosts in
21
21
photorefractive applications. The first example of this application used a copolymer that
incorporated both carbazole units and a non-linear chromophore pendant to the same siloxane
polymer chain.34 This approach allowed for tuning of the component ratios by modifying the
polymer stoichiometry without fear of phase separation or crystallization issues. Using this
approach, Bratcher et al. produced polymers with both good morphological stability and
moderate photorefractive gain coefficients (2.8 cm-1). It was discovered later that polymers
containing only hole-transport groups could be used when doped with small molecule
photosensitizers and non-linear optical chromophores forming a simplified photorefractive
system. Such doped systems were first described by Moon et al. using PSX as a host material to
achieve a photorefractive systems with exceptional gain coefficients (>390 cm-1) and stable
morphological properties.35,36 Building on these studies, other photorefractive systems
incorporating hole transporting moieties other than carbazole have been reported.37-41 These
alternate hole transporting polymers carry over many of the benefits of PSX while offering
improved response time due to the greater photoconductivity of many hole transport materials as
compared to carbazole.
More complex silicone structures have also been functionalized with organic semiconducting
groups. Ladder type polysilsesquioxanes hybrid materials have been developed by reacting a
trialkoxy substituted organic semiconductor under specific hydrolytic condensation conditions.
Using this method, a carbazole substituted polysilsesquioxane has been reported (2-3) and
characterized.42 This material shows many similar properties to PSX and its derivatives
including good solution processibility and minimized excimer formation upon photoexcitation.
Uniquely, this ladder type polymer has a glass transition temperature of 95 °C. This value is
significantly higher than that found for PSX derivatives and is attributed to the more rigid
ladder-type silicone backbone. The polymer readily forms glassy films from solution and was
demonstrated to function as a hole transporting polymer and host in a simple single layer OLED.
This strategy has also been applied to perylene bisimides, a common electron transporting
material.43 Upon condensation, the alkoxysilane functionalized monomers produces a thermally
stable, film forming polymer. This polymer is found to have an exceedingly high glass transition
of ~310 °C and stable electrochemistry that resembles the monomeric perylene bisimide.
22
22
2.3.4.2 Cross-linked Films
Based on the results and chemistry of silicones outlined above, it should come as no surprise that
the idea of silicone hybrid material evolved towards the use of cross linked films. Cross-linked
films are occasionally more desirable as semiconducting layers in organic electronic devices than
their soluble counter parts for several reasons. The principal reason is due to the insolubility
found in most cross-linked films. This allows solution processing of additional functional layers
on top of a cross-linked layer without the potential for interlayer mixing. By incorporating cross-
linked layers into a complex device structure, sequential solution processing steps can used to
deliver a multi-layered structure. These kinds of multi-layered solution processed devices can
normally only be achieved by using orthogonal solvent systems for different layers, a strategy
which is inherently limited. Cross-linked films also can result in system morphology that is
significantly stabilized over time. Because molecular orientations are locked in by the cross
linking process, crystallization or phase separation observed in other organic semiconductor
types can be avoided for increased device stability.
Scheme 2-3. Cross section of an OLED device and examples of siloxane containing materials applied at either the ITO/hole transport layer interface or in the bulk of the functional layers (as indicated by color coding).
2-6
2-5
2-4
2-7 R = -SiCl3
2-8 R = -Si(OMe)3
23
23
The first example of using a polycondensation process to cross-link organic semiconductor films
relied on the sol-gel reaction of alkoxysilane functionalized organic semiconductors.44 By
preparing analogues of a known emissive material (2-4) and electron (2-5) and hole transporting
(a carbazole derivative) layers (Scheme 2-3) with triethoxysilane groups, homogeneous films
could be achieved by depositing the molecules under typical sol-gel conditions. Using these
conditions, alkoxysilane groups hydrolyze, self-condense and cross-link with each other11 to
form stable films. The utility of such cross-linked films was demonstrated by depositing multiple
layers on top of one another to achieve a multilayer OLED structure. Because each organic layer
is cross-linked and insoluble, subsequent layers do not disturb the interface of the previous layer.
OLEDs produced using this method had high yet reasonable turn on voltages (~13 V) and rather
average external quantum efficiencies (<0.5 %, for unoptimized devices).44
Another approach to cross-linked layers relied on the use of trichlorosilane groups as
polymerizable functionalities incorporated into triarylamine molecules (such as 2-6, 2-7 or 2-8 in
Scheme 2-3).45 The hydrolytically unstable trichlorosilane groups rapidly hydrolyze, condense
and react/crosslink with each other upon contact with atmospheric moisture in a sol-gel
process.11 These materials were found to yield high quality homogeneous cross-linked films
when spin coated onto a transparent indium-tin oxide (ITO) substrates under ambient conditions.
The resulting films were found to have very good mechanical and thermal properties as would be
expected for a highly cross-linked film. More importantly, the films retained the useful
electrochemical properties of the triarylamine moieties. Practical utility of this approach was
demonstrated by constructing simple bilayer OLEDs using this cross-linked layer as a hole-
transport layer. The resulting devices displayed low turn on voltages (~6 V) and typical external
quantum efficiencies for such device architectures (~0.2%). Combined with the results
highlighted in the preceding paragraphs, these devices again demonstrate that cross-linking
triarylamines using sol-gel chemistry does not greatly diminish their hole transporting properties
and are a way to produce insoluble hole transporting layers.
The use of cross-linked organic semiconductor layers of triarylamines has also been
demonstrated as a way to increase the performance of fluorescent OLED devices through
improved hole injection and exciton confinement. Several studies based on these interlayers have
24
24
yielded optimized fluorescent devices with excellent performance based on both solution
processed46 and multi-layered vacuum deposited OLED architectures.47,48 This increase in device
performance is the result of modifying the electronic properties of the electrode to better work
with adjacent organic semiconducting materials. In particular, the use of these crosslink organic
semiconducting layers can modify the energy levels of the electrode to improve charge
injection/collection while blocking unwanted opposite charges. Similar results have also been
achieved using interlayers derived from the more hydrolytically stable alkoxysilanes.49 The use
of such alkoxysilanes allows for easier synthesis, purification, and handling of the final materials
while achieving similar results. A highly optimized vacuum deposited device incorporating a
cross-linked interlayer yielded a maximum external quantum efficiency of ~4.4% and a low turn-
on voltage of ~4.5 V.50
Recently, phosphorescent OLEDs have also been produced using cross-linked triarylamines as
hole transport layers.51 In this example by Lim et al, the alkoxysilane functionalized triarylamine
was deposited as a hole-transport layer and cross-linked. An emitting layer containing a
phosphorescent dopant in a polymeric host material was solution deposited on top followed by
several vacuum layers. As expected, the performance of this phosphorescent device exceeded
that of the aforementioned fluorescent devices with higher external quantum efficiencies (up to
6.4%) and similarly good luminance and turn-on voltages.
The utility of such crosslinked films prepared using sol-gel chemistry has also been
demonstrated in the area of xerographic photoreceptors. In this case a triarylamine containing
two reactive diisopropyl silane groups was prepared by reaction of a carboxylated precursor with
3-iodopropyl diisopropyl silane (2-9, Figure 2-2). Subsequent sol-gel processing of the
triarylamine in the presence of a second electronically inert material (derived from
hydrosilylation of technical grade divinyl benzene) following by coating onto a photoreceptor
device yielded high quality, hard hole conducting films. When compared to typical non-
crosslinked coatings for xerographic photoreceptors, these hybrid films were found to have
superior mechanical properties and better resisted abrasive wear while maintaining printed image
quality.52-54
25
25
Figure 2-2. Example of siloxane containing triarylamie applied in a xerographic photoreceptor.
Another application for these kinds of materials is as a thin interlayer on electrodes for organic
electronic devices. Transparent conducting electrodes for OPV and OLED devices are useful for
obvious reasons. However, these metal oxide electrodes have the disadvantage of having a
hydrophilic surface and energy levels that may not match complementary organic materials
contacting the electrode within a OPV or OLED. Their hydrophilic surface properties can cause
issues when attempting to coat these electrodes with hydrophobic organic semiconductors. This
mismatch in surface energies can result in surface wetting issues and delamination of organic
layers upon heating. It has been shown that silane functionalized triarylamines can mitigate these
issues by acting as a compatibilizing layer for other organics.55, 56 Monolayers of triarylamines
can be prepared by coating hydroxyl-functionalized indium tin oxide (ITO) substrates with the
chloro or alkoxy silane (such as 2-6, 2-7 or 2-8 in Scheme 2-3) functionalized material under
inert conditions. This procedure results in the formation of a monolayer of hole-transporting
molecules that is self-limiting in its thickness from a lack of atmospheric moisture needed for
further reaction. Using this modified ITO layer as an anode for a bilayer OLED, greatly
enhanced thermal stability and charge injection into the organic layer were found as compared to
both unmodified ITO and ITO modified with a typical organic hole injection layer such as
PEDOT:PSS.56 This enhanced stability was attributed to better interfacial adhesion between the
layers of the device.
This approach has also been extended to cross-linkable interlayers for organic photovoltaics.
Much like for OLEDs, OPVs benefit from electrode interlayers to improve both surface wetting
and electronic properties for better compatibility with subsequent layers. Silyl chloride
functionalized triarylamines (such as 2-6, 2-7 or 2-8 in Scheme 2-3) have been used as
2-9
26
26
interlayers for prototypical bulk heterojunction OPVs based on conjugated polymers and
fullerenes as electron donors and electron acceptors, respectively. For OPVs with either
polyphenylenevinylene (MDMO-PPV)57,58 or poly-3-hexylthiophene (P3HT)59 as donor
polymers, it was found that the cross-linkable triarylamines blended with a high mobility
polymer functioned as a suitable replacement with superior performance when compared to the
prototypical interlayer poly(ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) in
the case of OPVs based on MDMO-PPV. For P3HT based devices, almost identical performance
was achieved.
Figure 2-3: Example of siloxane containing material used as an electron selective interlayer for OPV.
Electron selective interlayers based on siloxane chemistry have also been demonstrated to act as
interlayers for organic photovoltaics.60 Conceptually this differs from the above example as this
interlayer needs to selectively accept negative charges instead of positive charges. Hains et al
showed a functionalized perylene bisimide derivative (2-10, Figure 2-3) could form an electron
selective interlayer on ITO in an inverted P3HT/fullerene based device. The resulting devices
showed fairly mediocre performance which improved upon doping the layer with ionic
components and a high mobility conjugated polymer. Despite the performance of these initial
results, we feel the idea of developing electron selective cross-linking systems should be of great
interest to those interested in the development of inverted OLEDs and OPVs.
2.3.4.3 Discrete Molecules
2.3.4.3.1 Silsesquioxane Based Semiconductors
Despite the propensity for siloxane functionalities to undergo polymerization and cross-linking
reactions, there are many examples of discrete siloxane structures in organic electronic materials.
The most prominent of which are silsesquioxane hybrid materials. Silsesquioxanes are a class of
silicon based materials with an empirical formula of RSiO2/3.61 This is a ratio of silicon to
2-10
27
27
oxygen between that of pure silica (SiO2) and silicones. This unique bonding arrangement results
in a cage structure that can be a discrete assembly, a partially defined unit, or a macromolecular
structure. These are all commonly referred to as polysilsesquioxanes (POSSs). Several discrete
assemblies are commonly encountered and the naming of different units follows a Tn naming
convention, where n is the number of silicon atoms. The most common unit, T8, has 8 silicon
atoms comprising a cubic structure that allows for up to 8 functionalities to be present at each of
the vertices of the cube (Figure 2-4).
Figure 2-4. Structure of common silsesquioxane-T8 synthetic precursors.
POSSs are unique compared to other silicone classes in that the discrete T8 unit is
conformationally rigid. Consequently, their use in organic electronic semiconductors is primarily
to act as a rigid inert central unit which can be functionalized with many different active
semiconducting moieties. This hybridization generally results in materials with better thermal
stability, solution processibility, improved film formation, and reduced intermolecular
interactions between the semiconducting moieties. This strategy has also been used to engineer
small molecules which have poor film forming properties into hybrid materials which can be
readily solution processed. The functionalization of POSS cores with organic semiconducting
structures has emerged as a way to produce novel and useful materials, primarily for OLED
applications.
28
28
Figure 2-5: Examples of several POSS-T8 derivatives functionalized with organic semiconducting groups.
The first examples of hybrid POSS strategy involved complete or partial coupling of hole
transporting groups onto the periphery of the T8 unit. In work by Sellinger et al.,62 an octa-vinyl
functionalized T8 was poly-functionalized with a two nitrogen centred triarylamine by the
Mizoroki-Heck reaction (see Scheme 2-1) resulting in a mixture of hybrid materials with 3 to 10
substitutions. This surprisingly large range of substitutions suggests very poor selectivity with
this synthetic strategy or an inability to push the reaction to completion. Regardless, the final
triarylamine functionalized T8 material was found to form stable amorphous glasses from
solution casting. Films of the material showed identical photoluminescence to samples in
2-13
2-14
2-12
2-11
29
29
solution indicating a lack of aggregation in the solid state. The new material and the
bare/precursor triarylamine were used as hole transport layers with tris(8-
hydroxyquinolinato)aluminium (AlQ3) in a standard 2-layer OLED configuration. Both devices
performed similarly indicating that POSS-functionalization had a negligible impact on the
electronic properties of the triarylamine while altering its physical properties.
Complete substitution of the POSS core has been achieved using the hydrosilylation approach
(see Scheme 2-1). In this strategy, N-vinylcarbazole was reacted with
octakis(dimethylsiloxy)silsequioxane using Karstedt’s catalyst under hydrosilylation conditions
to yield a hybrid POSS (Figure 2-5, 2-11).63 The resulting compound is very thermally stable (up
to 400 °C) and readily forms stable amorphous glasses from a melt. Much like PSX polymers
and the aforementioned example by Sellinger et al, photoluminescent spectra shows no excimer
formation. This again suggests that this approach results in a material with negligible interactions
between neighbouring carbazole units in the solid state. Hydrosilylation appears to be far more
selective and controllable approach (yielding 8 substitutions) as compared to the Mizoroki-Heck
approach where partial and/or over-functionalization appears to be common.64 Other examples of
the functionalization of POSS using hole transporting units have been reported including using
other carbazoles,65 and a variety of triarylamines.66
The functionalization of POSS cores can also be used to obtain novel light emitting materials for
use in OLEDs. The benefit to this approach relies on the known ability of POSS
functionalization to minimize interactions between semiconducting molecules (as highlighted in
the preceding paragraphs). By functionalizing a POSS with fluorescent units, the intermolecular
interactions between these fluorescent units can be limited which in turn improves the
fluorescent efficiency of these materials in the solid-state. This is very desirable as high solid-
state photoluminescent yields are a critical parameter for the production of highly efficient
OLEDs.67
The successful application of this idea was first shown by the synthesis of a POSS core
functionalized with oligofluorenes and applied in a blue emitting OLED.68 Despite poor
performance for unoptimized devices, the hybrid POSS materials performed better than their
30
30
polymeric or small molecule counterparts. The reason for this difference was again ascribed to
the reduced intermolecular interactions between the flat, crystalline oligofluorenes that normally
quench luminescence in the solid-state. Another striking example of this of this idea was shown
by the Sellinger group where the highly planar and crystalline pyrene fluorophore was
hybridized with a POSS core.64 The hybrid pyrene materials easily formed amorphous films with
excellent morphological stability and high photoluminescence quantum yields. OLEDs made
from this material performed quite well with external quantum efficiencies peaking at 2.63%,
high luminescence (36000 cd/m2), and low turn-on voltages (3.1 V). From these studies, it is
clear that hybrid POSS materials can produce highly luminescent films containing chromophores
that normally would not emit strongly in the solid-state.
Building on this strategy, POSS cores with up to three different fluorophores have been
synthesized and studied (Figure 2-5, 2-12).69 By using various combinations of blue, yellow, and
orange emitters, OLEDs with electroluminescence from each of the different chromophores was
demonstrated. Unfortunately, Forehlich et al showed the small spatial separation and energy
level overlap of the multiple emitters resulted in a great deal of energy transfer from the higher
energy blue emitter to the lower energy orange or yellow emitters. This resulted in unbalanced
emission which may limit the further exploration of POSS materials with multiple emitters.
Higher OLED efficiencies have been achieved by incorporating phosphorescent emitters onto
POSS cores. The first such effort used an analogue of the well-known Ir(ppy)2(acac) phosphor to
produce a fully derivatized POSS derivative with 8 emitting Ir(ppy)2(acac) moieties.70 Quantum
yields of the hybrid POSSs were moderately higher than the lone phosphors indicating the utility
of incorporation of the rigid POSS core. Single layered OLEDs showed very modest
performance with high turn-on voltages (12 V) and low brightness (max of 1172 cd/m2). Yang et
al improved on this result by synthesizing additional POSS derivatives with three different
analogues of known iridium based emitting complexes.71 Single layer OLEDs with high
efficiencies were achieved by blending the POSS derivatives into a mixture of PVK and an
electron transporting material. Using this approach, high efficiency red, green and blue devices
were demonstrated with external quantum efficiency values of up to 8.4%, high luminance and
low driving voltages. Blending of the three emitters was shown to produce white light OLEDs.
31
31
In the same study, even higher efficiencies were found when the hydrid POSS derivatives
containing 7 carbazole groups and 1 iridium emitter were synthesized. By chemically combining
hole transporting groups and emitting groups onto the same POSS core, multi-functional
materials were realized. Devices based on these mixed emitting and hole transporting derivatives
showed better performance which is attributed to decreased interaction between iridium
complexes and improved charge transport. Most significantly, single layered devices using this
multifunctional hybrid POSS material in the absence of additional hole or electron transporting
materials produced a device with moderate efficiency (1.3%). This demonstrated that
incorporating mixed functionalities onto a single POSS core is a promising strategy to efficient
OLEDs with significantly simplified structures. Analogous materials using platinum based
emitters have also been demonstrated (Figure 2-5, 2-13).72 These materials showed similar
function and efficiency to those made with iridium emitters.
POSS functionalization with other organic semiconducting functionalities has been demonstrated
but not explored as thoroughly as the above examples. POSS derivatives with electron
transporting 2,5-diphenyl-1,3,4-oxadiazole groups (Figure 2-5, 2-14) have been synthesized
although no electron transporting capability was demonstrated.73 Derivatives containing boron
dipyrromethene dyes have also been reported.74 Both of these cases show better thermal stability
and photoluminescent efficiency for the POSS functionalized molecules as compared to their
small molecule equivalents.
The ability of POSS cores to be decorated with different functional groups may open the
possibility of even more complex materials bearing multiple transporting groups and emitting
materials with minimal synthetic effort. Given that adding functional groups to POSSs seems to
only improve thermal properties and solution processibility, this approach may serve as a general
and facile way to improve the physical properties of many other known organic semiconductors
for a variety of device applications. In our opinion, further exploration of this strategy is
certainly warranted.
32
32
2.3.5 Conclusions and Outlook
In summary, the use of electronically inert silicone and siloxane fragments in organic
semiconducting materials has been outlined. Both the common chemistries and synthetic
concerns needed to obtain these materials have been reviewed as well as different examples of
polymeric, cross-linked and discrete hybrid materials comprised of silicones, silsesquioxanes and
siloxanes. Despite the large range of materials used for a variety of applications, all of these
materials can be tied together with a common theme: the use of silicone and siloxanes to control
the physical properties of the final material without altering the inherently useful electronic
properties of the organic semiconducting fragment. This has been demonstrated across a variety
of different material types proving that this strategy is a powerful synthetic tool available to
engineer new and potentially better performing materials for organic electronic devices.
Finally, this field has been slowly growing over a long period of time resulting in a number very
interesting and novel uses of these hybrid materials in various organic electronic devices from
various independent research streams. But, many of these research streams have not overlapped
greatly despite some of the common goals and techniques used between groups. As such, it is
hoped that this tutorial review has been able to put these various research efforts into context
with one another and may potentially be used to inspire subsequent efforts within the field.
2.4 References
1. A. C. Grimsdale, K. L. Chan, R. E. Martin, P. G. Jokisz and A. B. Holmes, Chem. Rev., 2009,
109, 897-1091.
2. L. Xiao, Z. Chen, B. Qu, J. Luo, S. Kong, Q. Gong and J. Kido, Adv. Mat., 2011, 23, 926-952.
3. A. W. Hains, Z. Liang, M. A. Woodhouse and B. A. Gregg, Chem.l Rev., 2010, 110, 6689-
6735.
4. Y.-J. Cheng, S.-H. Yang and C.-S. Hsu, Chem. Rev., 2009, 109, 5868-5923.
5. P. M. Borsenberger and D. S. Weiss, Organic Photoreceptors for Xerography, Marcel Dekker
Inc., New York, 1998.
6. S. Allard, M. Forster, B. Souharce, H. Thiem and U. Scherf, Angew. Chemie Inter. Ed., 2008,
47, 4070-4098.
7. S. R. Forrest and M. E. Thompson, Chem. Rev., 2007, 107, 923-925.
8. Y. Shirota and H. Kageyama, Chem. Rev., 2007, 107, 953-1010.
33
33
9. M. Androit, S. H. Chao, A. Colas, S. Cray, F. de Buyl, J. V. Degroot, D. A., T. Easton, J. L.
Garaud, E. Gerlach, F. Gubbels, M. Jungk, S. Lealey, J. P. Lecomte, B. Lenoble, R. Meeks,
A. Mountney, G. Shearer, S. Stassen, C. Stevens, X. Thomas and A. T. Wolf, in Inorganic
Polymers, eds. R. D. Jaeger and M. Gleria, Nova Science Pub Inc New York, 2007, pp. 61-
161.
10. M. A. Brook, Silicon in Organic, Organmetallic, and Polymer Chemistry, John Wiley &
Sons, New York, 2000.
11. L. L. Hench and J.K. West, Chem. Rev., 1990, 90, 33-72.
12. B. Marciniec, Comprehensive Handbook on Hydrosilylation, 1st edn., Pergamon, 1992.
13. B.D. Karstedt, US 3,775,452. November 27,1973.
14. J. L. Speier, J. A. Webster and G. H. Barnes, J. Am. Chem. Soc., 1957, 79, 974-979.
15. S. Rubinsztajn and J. Cella, Macromolecules, 2005, 38, 1061-1063.
16. M. A. Brook, J. B. Grande and F. Ganachaud, Adv. Polym. Sci., 2010, 235, 161-183.
17. M. J. Gretton, B. A. Kamino and T. P. Bender, Macromolecules, 2011.
18. B. A. Kamino, J. Castrucci and T. P. Bender, Silicon, 2011, 3, 125-137.
19. B. A. Kamino, J. B. Grande, M. A. Brook and T. P. Bender, Org. Lett., 2011, 13, 154-157.
20. B. A. Kamino, B. Mills, C. Reali, M. J. Gretton, M. A. Brook and T. P. Bender, J. Org.
Chem., 2011.
21. S. Rubinsztajn and J. A. Cella, Macromolecules, 2005, 38, 1061-1063.
22. J. B. Grande, D. B. Thompson, F. Gonzaga and M. A. Brook, Chem. Comm., 2010, 27,
4988-4990.
23. D. J. Parks, J. M. Blackwell and W. E. Piers, J. Org. Chem. , 2000, 65, 3090-3098.
24. T. Mizoroki, K. Mori and A. Ozaki, Bulletin of the Chemical Society of Japan, 1971, 44,
581.
25. R. F. Heck and J. P. Nolley, J. Org. Chem., 1972, 37, 2320-2322.
26. I. P. Beletskaya and A. V. Cheprakov, Chem. Rev., 2000, 100, 3009-3066.
27. P. Strohriegl, Makromol. Chem., Rapid Commun., 1986, 7, 771-775.
28. M. Lux and P. Strohriegl, Makromol. Chem., Rapid Commun., 1987, 188, 811-820.
29. M. Hennecke and P. Strohriegl, Makromol. Chem., Rapid Commun., 1988, 189, 2601-2609.
30. H. Domes, R. Fischer, D. Haarer and P. Strohriegl, Makromol. Chem., Rapid Commun.,
1989, 190, 165-174.
34
34
31. M. Yokoyama, T. Tamamura, M. Atsumi, M. Yoshimura, Y. Shirota and H. Mikawa,
Macromolecules, 1975, 8, 101-104.
32. K. Meerholz, B. L. Volodin, Sandalphon, B. Kippelen and N. Peyghambaraian, Nature,
1994, 371, 497-500.
33. W. E. Moerner, S. M. Silence, F. Hache and G. C. Bjorklund, J. Opt. Soc. Am. B., 1994, 11,
320-330.
34. M. S. Bratcher, M. S. DeClue, A. Grunnet-Jepsen, D. Wright, B. R. Smith, W. E. Moerner
and J. S. Siegel, J. Am. Chem. Soc., 1998, 120, 9680-9681.
35. I. K. Moon, D. Yoo, H. S. Moon, D.-H. Shin, W. S. Jahng, H. Chun and N. Kim, Molecular
Crystals and Liquid Crystals, 2000, 349, 43-46.
36. H. Chun, I. K. Moon, D.-H. Shin and N. Kim, Chem. Mater, 2001, 13, 2813-2817.
37. D. Wright, U. Gubler, W. E. Moerner, M. S. DeClue and J. S. Siegel, J. Phys. Chem. B,
2003, 107, 4732-4737.
38. S. H. Lee, W. S. Jahng, K. H. Park, N. Kim, W.-J. Joo and D. H. Choi, Macromolecular
Research, 2003, 11, 431-436.
39. I. K. Moon, J.-W. Oh and N. Kim, Journal of Photochemistry and Photobiology A:
Chemistry, 2008, 194, 327-332.
40. I. K. Moon, J.-W. Oh and N. Kim, Journal of Photochemistry and Photobiology A:
Chemistry, 2008, 194, 351-355.
41. I. Moon, C. Choi and N. Kim, Journal of Photochemistry and Photobiology A: Chemistry,
2009, 202, 57-62.
42. S.-S. Choi, H. S. Lee, S. S. Hwang, D. H. Choi and K.-Y. Baek, J. Mat. Chem., 2010, 20,
9852.
43. W. Fu, C. He, S. Jiang, Z. Chen, J. Zhang, Z. Li, S. Yan and R. Zhang, Macromolecules,
2011, 44, 203-207.
44. T. Dantas de Morais, F. Chaput, K. Lahlil and J. P. Boilot, Adv. Mater., 1999, 22, 107-112.
45. W. Li, W. Q., J. Cui, H. Chou, S. E. Shaheen, G. E. Jabbour, J. D. Anderson, P. Lee, B.
Kippelen, N. Peyghambaraian, N. Armstrong and T. J. Marks, Adv. Mater., 1999, 11, 730-
734.
46. H. Yan, P. Lee, N. R. Armstrong, A. Graham, G. A. Evmenenko, P. Dutta and T. J. Marks,
J. Am. Chem. Soc., 2005, 127, 3172-3183.
35
35
47. Q. Huang, J. Cui, J. G. C. Veinot, H. Yan and T. J. Marks, Appl. Phys. Lett., 2003, 82, 331.
48. Q. Huang, G. A. Evmenenko, P. Dutta, P. Lee, N. R. Armstrong and T. J. Marks, J. Am.
Chem. Soc., 2005, 127, 10227-10242.
49. J. Li and T. J. Marks, Chem. Mater, 2008, 20, 4873-4882.
50. Q. Huang, J. Li, T. J. Marks, G. A. Evmenenko and P. Dutta, J. Appl. Phys., 2007, 101,
093101.
51. Y. Lim, Y.-S. Park, Y. Kang, D. Y. Jang, J. H. Kim, J.-J. Kim, A. Sellinger and D. Y. Yoon,
J. Am. Chem. Soc., 2011, 133, 1375-1382.
52. T. P. Bender, US 7,390,599. June 24, 2008.
53. T. P. Bender, J.F. Graham, Y. Gagnon, C.K. Hsiao, N.X. Hu and Y. Qi, US 7,348,447.
March 25, 2008.
54. T. P. Bender and N.X. Hu, US 7,262,314. August 28, 2007.
55. J. Cui, Q. Huang, Q. Wang and T. J. Marks, Langmuir, 2001, 17, 2051-2054.
56. J. Cui, Q. Huang, J. G. C. Veinot, H. Yan, Q. Wang, G. R. Hutchinson, A. Richter, G., G. A.
Evmenenko, P. Dutta and T. J. Marks, Langmuir, 2002, 18, 9958-9970.
57. A. W. Hains and T. J. Marks, Appl. Phys. Lett., 2008, 92, 023504.
58. A. W. Hains, J. Liu, A. B. F. Martinson, M. D. Irwin and T. J. Marks, Adv. Funct. Mat.,
2010, 20, 595-606.
59. A. W. Hains, C. Ramanan, M. D. Irwin, J. Liu, M. R. Wasielewski and T. J. Marks, ACS
Appl. Mat. Inter., 2010, 2, 175-185.
60. A. W. Hains, H.-Y. Chen, T. H. Reilly and B. A. Gregg, ACS Appl. Mat. Inter., 2011.
61. M. I. Ronald H. Baney, Akihito Sakakibara, Toshio Suzuki, Chem. Rev. , 1995, 95, 1409-
1430.
62. A. Sellinger, R. Tamaki, R. M. Laine, K. Ueno, H. Tanabe, E. Williams and G. E. Jabbour,
Chem. Comm., 2005, 3700.
63. I. Imae, 2005, 5937, 59371N-59371N-59378.
64. M. Y. Lo, C. Zhen, M. Lauters, G. E. Jabbour and A. Sellinger, J. Am. Chem. Soc., 2007,
129, 5808-5809.
65. C.-C. Cheng, C.-H. Chien, Y.-C. Yen, Y.-S. Ye, F.-H. Ko, C.-H. Lin and F.-C. Chang, Acta
Materialia, 2009, 57, 1938-1946.
66. M. Y. Lo, K. Ueno, H. Tanabe and A. Sellinger, The Chemical Record, 2006, 6, 157-168.
36
36
67. S. Nowy, B. C. Krummacher, J. r. Frischeisen, N. A. Reinke and W. Brütting, J. Appl. Phys.,
2008, 104, 123109.
68. H.-J. Cho, D.-H. Hwang, J.-I. Lee, Y.-K. Jung, J.-H. Park, J. Lee, S.-K. Lee and H.-K. Shim,
Chem. Mater., 2006, 18, 3780-3787.
69. J. D. Froehlich, R. Young, T. Nakamura, Y. Ohmori, S. Li and A. Mochizuki, Chem. Mater,
2007, 19, 4991-4997.
70. K. Chen, Y. Chang, S. Yang and C. Hsu, Thin Solid Films, 2006, 514, 103-109.
71. X. Yang, J. D. Froehlich, H. S. Chae, S. Li, A. Mochizuki and G. E. Jabbour, Adv. Funct.
Mat., 2009, 19, 2623-2629.
72. X. Yang, J. D. Froehlich, H. S. Chae, B. T. Harding, S. Li, A. Mochizuki and G. E. Jabbour,
Chem. Mater., 2010, 22, 4776-4782.
73. X. Wang, S. Guang, H. Xu, X. Su and N. Lin, J. Mat. Chem., 2011, 21, 12941-12948.
74. M. Liras, M. Pintado-Sierra, F. Amat-Guerri and R. Sastre, J. Mat. Chem., 2011, 21, 12803-
12811.
37
37
Chapter 3: Effect of Triarylamine Structure on the Photoinduced Electron Transfer to Boron Subphthalocyanine
3.1 Executive Summary
This chapter contains a paper published in the Journal of Physical Chemistry C.
Brett A. Kamino, Graham E. Morse, Timothy P. Bender, 2011, Journal of Physical Chemistry
C, 115 (42), 20716-20723. Please note that the experimental section and supplemental information can be found in the appendices in section 12.1. Figure and Schemes are reprinted with permission. Copyright 2011 American Chemical Society
In this first chapter, we investigate how triarylamines interact electronically with an electron
acceptor, boron subphthalocyanine (BsubPc). BsubPc was chosen because it is actively being
studied in our laboratory as an electron acceptor in organic photovoltaics. This work was
originally performed in order to develop optimized photovoltaic devices using these two classes
of materials. To help with this process we needed to understand how triarylamines and BsubPcs
work together using basic photochemical techniques. Specifically, we were interested in the
photoinduced electron transfer reaction between these two materials, a key step in the generation
of power from an organic photovoltaic device.
More broadly, this paper gave me an opportunity to explore how to tune the electrochemical
properties of triarylamines over a wide range. This exploration contrasts somewhat to the bulk of
my thesis in that we were not interested in physical state of the triarylamines. Because of this,
I’ve opted to include it as the first research chapter of my thesis to illustrate how triarylamines
can be tuned over very wide range electrochemical properties. The ability to precisely control
triarylamine electrochemistry learned in this paper was applied over the remainder of my thesis
when trying to develop novel materials with unique physical properties. As well, it provides
some interesting design criteria and thoughts on how silicone-hybridized triarylamines might
eventually be incorporated into future organic photovoltaic devices.
38
38
3.2 Statement of Contributions
The authorship of this paper is as follows: Brett A. Kamino, Graham Morse, Timothy P. Bender.
Graham Morse contributed by performing fluorescence quenching experiments on a number of
off-the-shelf triarylamines (3-1a, 3-1e-i). The remainder of the fluorescence quenching
experiments was performed by me. All synthesis and characterization of new materials, and use
of theoretical framework was performed by me. The article was entirely written by me with input
from Prof. Bender as corresponding author.
3.3 Paper
3.3.1 Abstract
The photoinduced electron transfer (PET) reaction between a phenoxy-boronsubphthalocyanine
derivative and a series of triarylamine electron donors was investigated. A series of triarylamines
ranging in oxidation potentials and number of redox centers was prepared to study the effect of
triarylamine structure on the photoinduced electron transfer (PET) reaction. In the case of
multiple nitrogen centers, the triarylamines were dendritic in nature and were synthesized by a
convergent strategy relying on successive C-N coupling and thermolytic deprotection steps. The
efficiency of the PET reaction was found to be exponentially dependent on the oxidation
potential of the triarylamine beyond a certain threshold. The free-energy change of the PET
reaction was estimated using the Rehm-Weller equation, and this framework could be used to
adequately explain the observed behavior of the system. We have concluded that the specific
structure of the triarylamine is not important in the PET reaction and that efficiency of electron
transfer is almost solely dictated by the oxidation potential of the triarylamine donor.
3.3.2 Introduction
Triarylamines are a very important class of materials for a number organic electronic
applications (see Chapter 1.3). Before we begin to explore how to tune and alter their physical
properties, more work is needed on understanding how their electronic properties can be altered.
In achieving this goal we are also granted the opportunity to study how different triarylamines
may interact electronically with other useful classes of material. Despite all of the work
performed on producing new triarylamine structures, there has been comparatively little done to
understand the effects of specific triarylamine molecular structures and their associated
39
39
substituents on electron transfer processes with complementary materials. One very important
factor affecting the ultimate performance of these devices is how well the triarylamines are able
to donate an electron into a complementary acceptor material upon photoexcitation of the
acceptor. Such an interaction can be an important factor in optimizing the charge separation and
charge extraction processes in an organic solar cell (for example) and thus improving device
efficiencies1 for a selected group or pairing of materials.2
In this paper, we study the effect of triarylamine chemical structure on photoinduced electron
transfer efficiencies to a light-absorbing electron acceptor. This was done by studying the
fluorescence quenching in solution of a model fluorescent electron acceptor with various
triarylamines acting as electron donors. For the fluorophore and electron acceptor, a soluble
boron subphthalocyanine (BsubPc) derivative was chosen: 3,4-
dimethylphenoxyboronsubphthalocyanine (3,4-DMPhO-BsubPc, Figure 3-1).3 Beyond its
pleasing magenta color, this acceptor was chosen because BsubPc derivatives are currently of
interest for application in both organic photovoltaics4 and organic light emitting diode devices.5
As well, the established position of its HOMO allows a wide range of triarylamine donors to be
used as fluorescent quenchers. While chloroboronsubphthalocyanine (Cl-BsubPc) is typically
used as an electron-donating material, recent studies have shown the potential of phenoxy-
substituted BsubPc derivatives to act as electron acceptors/n-type charge transporting materials.6
A series of triarylamines that spanned both a range of oxidation potentials and a variety of
conjugated molecular structures were paired with 3,4-DMPhO-BsubPc. Obtaining triarylamines
that include one or two nitrogen centers was facilitated by our previous work in the area and by
the straightforward synthesis of triarylamines with two nitrogen centers (such molecules are
commonly known in the literature). However, to access triarylamines with a higher number of
nitrogen centers and as a consequence very low oxidation potentials, we purposefully
synthesized dendritic triarylamines for this study. Such dendrimers possess a high degree of
conjugation and associated charge stabilization while maintaining reasonable solubility due to
their nonplanar structures. These unique attributes result in materials that contain very small
energy gradients7 and stable electrochemistry.8 They have been studied as models for charge
transfer9 as well as the generation of high-spin polycations.10 By synthesizing and adding these
40
40
dendritic structures to a series of more conventional structures, we hoped to better understand the
range of structural and electronic properties that may affect the photoinduced electron transfer
reaction between a triarylamine and 3,4-DMPhO-BsubPc.
3.3.3 Results and Discussion
A series of triarylamine donors were used or purposefully prepared to study their ability to act as
electron donors to 3,4-DMPhO-BsubPc upon photoexcitation. This series incorporates single
triarylamines(3-1a-i, Figure 3-1) bearing various combinations of electron-donating groups as
well as two nitrogen-centered triarylamines which are constructed with different molecular
fragments separating the two nitrogen centers (3-2a-c, Figure 3-1).
NNN
NNN
OMe
OMeMeO
MeOOMeOMe
OMeMeOOMe
OMeMeO
MeO
N
OMeMeO
OMe
N
CH3MeO
OMe
CH3
N
CH3H3C
OMe
CH3CH3
N
CH3H3C
CH3
CH3CH3
2a 2b 2c
N
CH3
CH3CH3
H3C
N
CH3H3C
CH3
CH3
N
CH3H3C
F
CH3
N
F
F
F
1a 1b 1c 1d
1e 1f 1g 1i
N
CH3H3C
CH3
1h
CH3 CH3
F
3,4-DMPhO-BsubPc
O
N
N
N
N NN
B
CH3
CH3
Figure 3-1: Structures of 3,4-DMPhO-BsubPc and the triarylamines used in this study (containing either one (3-1a-i) or two nitrogen centers (3-2a-c)).
The chemistry utilized to synthesize single or two-nitrogen centered triarylamines relies on either
Buchwald-Hartwig11 or Ullman amination to construct the necessary C-N linkages. The detailed
syntheses of compounds 3-1a-i are described elsewhere (Figure 3-1).12 Triarylamines with two
nitrogen centers (3-2a-c) were synthesized in a single step using conventional methods. Their
3-1a 3-1b 3-1c 3-1d
3-1e 3-1f 3-1g 3-1h 3-1i
3-2a 3-2b 3-2c
41
41
synthesis is illustrated in the Supporting Information accompanying this article (Figure S3-1). To
gain access to triarylamines containing multiple nitrogen centers as well as materials with very
low oxidation potentials, dendritic triarylamines were synthesized. The dendrimers were
prepared in a convergent approach utilizing an alternating C-N coupling and deprotection
sequence to systematically increase generation size (Scheme 3-1).
Scheme 3-1: Synthetic pathway towards triarylamine dendrimers (3-5b and 3-6b). Conditions (i) sodium tert-butoxide, bis(dibenzylideneacetone)palladium or palladium acetate (see experimental), tri-tert-butylphosphine, toluene, reflux. (ii) 1,2,3,4-tetrahydronaphthalene, 200 °C, overnight.
Catalytic hydrogenolysis of benzyl8 or diphenyl methyl7 protecting groups or the acid promoted
cleavage of a t-butylcarbamate (tBOC) group by trifluoroacetic acid have been used elsewhere to
deprotect diphenylamine moieties.9,10 We however, developed a simplified deprotection strategy
which avoided hydrogenolysis and the use of strong organic acids. This was necessitated by our
observation that the use of trifluoroacetic acid, which while considered to be a very weakly
oxidizing acid compared to mineral acids such as H2SO4 or HNO3 resulted in the oxidation of the
triarylamine dendrimers as evidenced by a bright green color present in the reaction medium
characteristic of the radical cation. We found that removal of the tBOC group was facilitated by
simple heating (thermolysis) at 200 °C.13 This reaction proceeds cleanly resulting in no
42
42
observable oxidized product and is performed best when a small amount of a high boiling
solvent (in this case tetralin) is added to help melt the substrate and lower the viscosity of the
melt. Using this synthetic strategy, dendrons up to the second generation were prepared in good
yields. Attempts to produce dendrons of a higher generation by this strategy resulted in partial
substitution, a limitation that is likely a result of steric factors. For each generation dendron, the
free amine was finally capped with a p-tolyl group resulting in dendrimers 3-5b and 3-6b. Both
dendrimers were isolated as fine white powders, and their purity and composition were
established by 1H NMR, mass spectroscopy, and size exclusion chromatography (SEC). 1H
NMR analysis of both the free amine and p-tolyl-capped dendrimers (3-5a-b and 3-6a-b,
respectively) resulted in many overlapping resonances in the aromatic region of the spectra. We
were unable to acquire satisfactory 13C NMR spectra for all but compound 3-6b. Solubilities in
benzene-d6 were too low to achieve a good signal-to-noise ratio. Attempts to obtain spectra in
chlorinated solvents (chloroform-d and dichloromethane-d2) quickly resulted in oxidation of the
dendrimers as evidenced by the evolution of a characteristic bright green color which is
attributable to the presence of the radical cation. The presence of the paramagnetic radical
cations prevented NMR analysis in these solvents. The dendrimers were run through a low
molecular weight size exclusion column, and the chromatograms show well-resolved peaks for
each molecule and illustrate the progression of molecular size between each generation as well as
the purity of each (Figure 3-2).
43
43
Figure 3-2: Size exclusion chromatograms of the triarylamine dendrimers (3-5a and 3-6a) and a
single triarylamine analogue (3-1a) as detected by UV-Vis absorbance.
With this broad series of triarylamines in hand, each previously unreported compound was
characterized by solution cyclic voltammetry to determine their relative oxidation potentials
(Table 3-1). The electrochemistry was performed in a dichloromethane solution with
tetrabutylammonium perchlorate as the supporting electrolyte at a scan rate of 50 mV/s. A
platinum disk working electrode, platinum wire counter electrode, and saturated Ag/AgCl
pseudo reference electrode were also used. A small amount of decamethylferrocene was added to
each sample as an internal standard. All oxidation potentials are corrected to the accepted half
wave oxidation potential of decamethylferrocene (-0.012 V vs. Ag/AgCl).13 Several
triarylamines used in this study (3-1a-i) have been previously characterized under identical
conditions, and the literature values were incorporated into our data set. All of the studied
triarylamines displayed at least a single well-defined and reversible oxidation. This allowed for
an accurate determination of the half-wave oxidation potentials of the entire series. With respect
to the range of half-wave oxidation potentials, triarylamines with single nitrogen centers ranged
3-1a
3-5b
3-6b
44
44
from 1138 to 654 mV vs. Ag/AgCl, while the two nitrogen-centered amines ranged from 693
mV for the weakly conjugated 3-2b to 417 mV vs. Ag/AgCl for the more conjugated 3-2a. The
triarylamine dendrimers extended this range of half-wave oxidation potentials down to 273 mV
for the second-generation dendrimer (3-6b), whereas the first-generation dendrimer (3-5b) was
found to have an oxidation potential of 471 mV vs. Ag/AgCl. The first generation dendrimer (3-
5b) was found to undergo two fully reversible one-electron oxidations which is consistent with
similar structures in the literature (Figure 3-3).9 Increasing the potential further resulted in a third
irreversible oxidation. The second-generation dendrimer (3-6b) undergoes three distinct and
reversible oxidation events (Figure 3-3) likely attributable to the large number of conjugated
nitrogen centers present in this molecule. Full voltammagrams for 3-2a-c, 3-5b, and 3-6b are
illustrated in Figures S3-2 and S3-3.
45
45
Table 3-2: Electrochemical oxidation potentials, fluorescence quenching efficiency, and free energy change upon photoinduced electron transfer reaction with 3,4-DMPhO-BsubPc for triarylamines (3-1a-i, 3-2a-c, 3-5b and 3-6b).
Compound
Number of
Redox
Centers
E1ox (mV vs.
Ag/AgCl) K (mol-1) ∆G∆G∆G∆GPETPETPETPET (eV)(eV)(eV)(eV)
3-1a 1 820 10.0 ± 1.82 -0.098
3-1b 1 735 14.4 ± 0.48 -0.187
3-1c 1 690 18.7 ± 0.80 -0.228
3-1d 1 654 23.4 ± 1.16 -0.260
3-1e 1 814 5.2 ± 0.21 -0.127
3-1f 1 844 4.9 ± 0.15 -0.132
3-1g 1 912 2.8 ± 0.23 -0.064
3-1h 1 981 0.7 ± 0.07 0.005
3-1i 1 1138 0* 0.045
3-2a 2 417 71.4 ± 4.28 -0.569
3-2b 2 693 18.4 ± 0.52 -0.284
3-2c 2 643 26.4 ± 0.17 -0.333
3-5b 3 471 44.6 ± 5.56 -0.561
3-6b 7 273 187.7 ± 6.89 -0.843
* Value obtained is less than experimental error, considered to be 0.
46
46
Figure 3-3: Solution electrochemistry of triarylamine dendrimers (3-5b, 3-6b) and a representative single triarylamine (3-1a). Voltammagrams are corrected to the internal standard decamethylferrocene (E1/2,red = -0.012 V vs. Ag/AgCl).
The ability of the complete series of triarylamines to undergo an electron transfer event with a
photoexcited BsubPc was investigated using a standard steady state fluorescence quenching
experiment in solution. The BsubPc (3,4-DMPhO-BsubPc) was prepared as a 1x 10-5 M solution
in anhydrous toluene having varying amounts of triarylamine present. The solution was
photoexcited at 550 nm, and the intensity of the emission peak at 578 nm was recorded. The
relative efficiency of the photoinduced electron transfer reaction was determined by the Stern-
Volmer (equation 3-1)
][10 QKF
F⋅+= (3-1)
where F0 is the fluorescence intensity without any quencher added; F is the fluorescence intensity
at quencher concentration [Q]; and K is the quenching coefficient. For each triarylamine, a plot
3-1a
3-5b
3-6b
47
47
of F0/F vs. [Q] (a Stern-Volmer plot) was found to be linear and gave a good correlation when
fitted with a linear regression. The fluorescence quenching efficiencies (K) are summarized in
Table 3-1. The quenching coefficients range from those where no significant quenching was
observed (3-1i) to relatively large quenching coefficients (3-6b). To determine the effect of
triarylamine structure and oxidation potential on the photoinduced electron transfer (PET)
process, the quenching coefficients were plotted against the electrochemical half-wave oxidation
potentials (Figure 3-4). From this plot, it is apparent that there is a correlation between oxidation
potential and quenching efficiencies. Triarylamines with stronger electron-donating substituents
or lower oxidation potentials had higher quenching efficiencies than triarylamines with high
potentials. Perhaps more surprisingly, the majority of the triarylamines showed an exponential
dependence of quenching coefficient with oxidation potential. This relationship deviates only for
the triarylamines with the highest oxidation potentials. Fitting a line through the nine best
quenchers results in a particularly good fit with R2 = 0.98. As the oxidation potential increases
past 825 mV (vs. Ag/AgCl), the quenching constant quickly drops off. For example, triarylamine
1i has the highest oxidation potential and did not quench 3,4-DMPhO-BsubPc significantly.
Figure 3-4: Experimentally determined Stern-Volmer constants (K) plotted against half-wave oxidation potentials (E1/2,ox) of the triarylamine donor. Error bars are not included as they are small relative to the size of the data marker point.
48
48
To better understand these observations and to confirm whether our system is behaving as a
normal photoinduced electron transfer system, the free energy change of the electron transfer
process was estimated using the Rehm-Weller equation.15 This correlation was developed for
measurements in polar solvents. Because our measurements are carried out in a nonpolar solvent
(toluene, ε = 2.38), a modified version of the Rehm-Weller equation is used to take into account
the measured redox potential differences in solvents used which are of different dielectric
constants as follows:16
+−
−+⋅+−−=∆
−+−+RR
e
RRR
eEAEDEG
DCMDAtoluene
exDCMredoxPET 21
21
41
21
21
4))()((
0
2
0
2
επεεπε (3-2)
where Eox(D) is this oxidation potential of the electron donor (triarylamine); Ered(A) is the
reduction potential of the acceptor (3,4-DMPhO-BsubPc); 3 Eex is the energy of the excitation; e
is the elementary charge; ε0 is the vacuum permittivity; εtouene and εDCM are the dielectric
constants of toluene and dichloromethane, respectively; R+ and R- are the average ion radii of the
donor and acceptor, respectively; and RDA is the average donor-acceptor distance (estimated as 6
Å).16a The average ion radii of the donor and acceptor molecules were roughly estimated using
calculated values for molecular volume assuming that the molecules are spheres. These
molecular volumes were obtained through molecular modeling calculations on each of the
molecules studied and are included in the Supporting Information (Table S3-1).17 The average
donor-acceptor distance was estimated from molecular dynamics simulations using molecular
mechanics force fields (MM+). Center to center separation distances typically varied between 5.5
and 6.5 Å; a median estimate of 6 Å was used for these calculations. The resulting ∆GPET values
(Table 3-1) were plotted against the measured Stern-Volmer constants (Figure 3-5). The plot
shows an expected trend; as the free energy change becomes more favorable, the fluorescence
quenching efficiency increases. As well, a decrease in quenching efficiency occurs near ∆GPET =
0 eV, thus confirming that our system is well behaved and fits well into this theoretical
framework. This observation is expected given the lack of thermodynamic driving force for the
PET to the photoexcited 3,4-DMPhO-BsubPc for ∆GPET > 0 eV and indicates that our system is
well behaved and can be described by the Rehm-Weller model over the range studied. Looking
at the quenching efficiencies of the materials with the most favorable energy changes, it is
interesting to note that no plateau in quenching efficiency is observed. A diffusion limited
plateau in quenching efficiency at high values of ∆GPET is predicted by Rehm-Weller theory and
49
49
is observed in most systems.18 In our case, it may simply be that no materials have a sufficiently
high enough ∆GPET value to result in diffusion limited electron transfer.
Figure 3-5: Experimentally determined Stern Volmer constant (K) plotted against the free energy change estimated by a modified Rehm-Weller equation (Eq. 3-2). Error bars are not included as they are small relative to the size of the data marker point.
When looking at this analysis, it should be emphasized that several assumptions were made in
the calculation of the Coulombic attraction energy term, particularly in regards to the ion radii
(R+ and R-) and the donor-acceptor distance (RDA). Regardless of the assumptions associated
with this calculation, several important observations can be drawn from the data. Looking first at
the effect of triarylamine structure on quenching efficiencies, there is no relation between
structure and the fluorescence quenching efficiency. Triarylamines with single or two nitrogen
centers of similar oxidation potentials have equivalent quenching efficiencies. Therefore, a
conclusion can be drawn that there is no need to synthesize dendritic triarylamines to act as
electron donors to BsubPcs. It can also be seen that once the PET reaction is energetically
favorable, the quenching efficiency very closely follows an exponential relationship with
solution oxidation potential. The one deviation from this behavior is for compound 3-1e which
has a similar oxidation potential to 3-1a but a much lower quenching efficiency. This may be
50
50
explained by the much bulkier substitution pattern (t-butyl vs methyl) intuitively suggesting that
bulky non-conjugated substituents inhibit the electron transfer process via a steric effect.
3.3.4 Conclusions
In summary, the effect of triarylamine structure and oxidation potential on the photoinduced
electron transfer (PET) reaction to 3,4-DMPhO-BsubPc was investigated. This was performed
using a series conventional triarylamines and novel triarylamine dendrimers which spanned a
large range of oxidation potentials, number of conjugated redox centers, and structures. Relying
on steady-state fluorescence quenching, it was found that two regimes of PET reactions could be
found. Under a certain oxidation potential, the quenching efficiency was found to scale
exponentially with oxidation potential of the triarylamine regardless of it chemical structure.
This implies that oxidation potential is the primary factor in determining the efficiency of
electron transfer in this system and that triarylamine structure is not particularly important for
this process. By placing our data into the Rehm-Weller theoretical framework we have
determined that this system is well behaved including the expected deviation from the
exponential dependence of quenching on the oxidation potential of the donor coinciding with a
loss of thermodynamic driving at values for ∆GPET > 0 eV. The results of this study will directly
aid in the design of triarylamines as effective electron donating materials to BsubPc derivatives.
It also suggests a general methodology by which other donor/acceptor materials can be selected
and optimized for PET.
3.3.5 References
1. Sariciftci, N. S.; Smilowitz, L.; Heeger, A. J.; Wudl, F. Science 1992, 258 (5087), 1474–1476.
2. Guchhait, A.; Pal, A. J. J. Phys. Chem. C 2010, 114, 19294 19298.
3. Morse, G. E.; Helander, M. H.; Stanwick, J.; Sauks, J. M.; Paton, A. S.; Lu, Z. H.; Bender, T. P. J. Phys. Chem. C 2011, 115, 11709–11718.
4. (a) Mutolo, K. L.; Mayo, E. I.; Rand, B. P.; Forrest, S. R.; Thompson, M. E. J. Am.
Chem. Soc. 2006, 128, 8108–8109. (b) Sullivan, P.; Durand, A.; Hancox, I.; Beaumont, N.; Mirri, G.; Tucker, J. H. R.; Hatton, R. A.; Shipman, M.; Jones, T. S. Adv. Energy
Mater. 2011, 1(3), 352-355. (c) Ma, B.; Miyamoto, Y.; Woo, C. H.; Frechet, J. M. J.; Zhang, F.; Liu, Y. Proc. SPIE 2009, 74161E.
51
51
5. Helander, M. G.; Morse, G. E.; Qiu, J.; Castrucci, J. S.; Bender, T. P.; Lu, Z. ACS Appl.
Mater. Interfaces 2010, 2, 3147–3152.
6. Morse, G. E.; Helander, M. G.; Maka, J. F.; Lu, Z.; Bender, T. P. ACS Appl. Mater.
Interfaces 2010, 2, 1934–1944.
7. (a) Ranasinghe, M. I.; Varnavski, O. P.; Pawlas, J.; Hauck, S. I.; Louie, J.; Hartwig, J. F.; Goodson, T. J. Am. Chem. Soc. 2002, 124, 6520–6521. (b) Hagedorn, K. V.; Varnavski, O.; Hartwig, J.; Goodson, T. J. Phys. Chem. C 2008, 112, 2235–2238.
8. Louie, J.; Hartwig, J. F. J. Am. Chem. Soc. 1997, 119, 11695–11696.
9. Hirao, Y.; Ito, A.; Tanaka, K. J. Phys. Chem. A 2007, 111, 2951–2956.
10. Hirao, Y.; Ino, H.; Ito, A.; Tanaka, K.; Kato, T. J. Phys. Chem. A 2006, 110, 4866–4872.
11. (a) Hartwig, J. F.; Kawatsura, M.; Hauck, S. I.; Shaughnessy, K. H.; Alcazar Roman, L. M. J. Org. Chem. 1999, 64, 5575. (b) Jiang, L.; Stephan, B. L. Palladium-Catalyzed
Aromatic Carbon-Nitrogen Bond Formation. Metal-Catalyzed Cross-Coupling
Reactions, 2nd ed.; de Meijere, A., Diederich, F., Eds.; Wiley-VCH: New York, 2004; Chapter 13.
12. Bender, T. P.; Graham, J. F.; Duff, J. M. Chem. Mater. 2001, 13, 4105–4111.
13. Rawal, V. H.; Jones, R. J.; Cava, M. P. J. Org. Chem. 1987, 52, 19.
14. Noviandri, I; Brown, K. N.; Fleming, D. S.; Fulvas, P. T.; Lay, P. A.; Masters, A. F.; Phillips, L. J. Phys. Chem. B 1999, 103, 6713.
15. Rehm, D.; Weller, A. Isr. J. Chem. 1970, 8, 259–271.
16. (a) Weller, A. Z. Phys. Chem. 1982, 133, 93–98. (b) Heitele, H.; Finckh, P.; Weeren, S.; Pöllinger, F.; Michel-Beyerle, M. E. J. Phys. Chem. 1989, 93, 5173–5179. (c) Perez, L.; Garcia-Martinez, J. C.; Diez-Barra, E.; Atienzar, P.; Garcia, H.; Rodriguez-Lopez, J.; Langa, F. Chem. Eur. J. 2006, 12, 5149–5157.
17. Molecule volumes were calculated by Spartan ’06 utilizing molecular mechanics with a MMFF force field.
18. (a) Dosche, C.; Mickler, W.; Löhmannsröben, H.-G.; Agenet, N.; Vollhardt, K. P. C. J. Photochem. Photobiol. A 2007, 188, 371–377. (b) Nad, S.; Pal, H. J. Phys. Chem. A 2000, 104, 673–680.
52
52
Chapter 4: Controlling the Physical and Electrochemical Properties of Arylamines Through the Use of Simple Silyl Ethers: Liquid, Waxy and Glassy Arylamines
4.1 Executive Summary
This chapter was published as a full paper in Silicon.
Brett A. Kamino, Jeffrey Castrucci, Timothy P. Bender 2011, Silicon, Vol. 3, No. 3, 125-137.
Figure and Schemes are reprinted with permission. Copyright 2011 Springer.
The work described in this chapter details our very first attempts at controlling the physical
properties of triarylamines through incorporation of silicon chemistry. Specifically, we were
interested in developing methods to produce liquid organic semiconductors, a group of materials
with very antithetical properties to traditional triarylamines. In this work, we incorporated bulky
silyl ethers onto the periphery of triarylamine structures to alter their properties. These new
materials were studied by differential scanning calorimetry and solution electrochemistry.
Different silyl ether groups were explored as were different triarylamine structures. At the time,
silyl ethers seemed like an ideal group to modify physical properties. They could be easily
introduced onto common triarylamine building blocks and their large steric bulk should have
prevented strong intermolecular interactions, thus minimizing crystallization. As well, they are
not known to be conjugated or electronically active, therefore their presence shouldn`t have a
large effect on the electronic properties of the base material.
Overall, this strategy proved marginally successful. Of the series of triarylamine, only a single
compound (4-5) would be isolated as a freely flowing liquid. As it turned out, any triarylamine
compound with more than one nitrogen centre remained a solid at room temperature. Some
compounds were even found to be highly crystalline despite the presence of these bulky groups.
While this was a somewhat disappointing outcome, several important discoveries were made that
impacted the direction of this project and of my thesis. Most importantly, we found a well-
behaved and easily synthesized liquid triarylamine (4-5). This compound later goes on to be used
as a model liquid organic semiconductor for our charge transport studies (Chapter 7). Secondly,
one multi-nitrogen centered compound (4-7) was found to be soluble in hexamethyldisiloxane
53
53
(MM). This was very interesting as MM is an inert and non-toxic fluid, as well it is a non-solvent
for practically everything but silicones. This is highly interesting as it may allow the solution
deposition of this molecule on top of other soluble derivatives on the basis of orthogonal solvent
processing. At the time we attempted to build up discrete layers through solution processing.
Unfortunately, these layers were difficult to study due to the very low glass transition
temperature of the compound. Future work in this area could be used to develop more
triarylamines and organic semiconductors that are soluble in MM fluid.
4.2 Statement of Contributions
The authorship of this paper is as follows: Brett A. Kamino, Jeffrey Castrucci, Timothy P.
Bender. Jeffrey Castrucci helped to synthesize and characterize four compounds (4-4a-d) as an
undergraduate student under my guidance. The remainder of the compounds were synthesized
and characterized by me. The paper was written by me and Prof. Bender as corresponding
author.
4.3 Paper
4.3.1 Abstract
The effect of silyl ether substitution on the physical and electrochemical properties of single and
two-nitrogen centered arylamines was explored. It was found that this substitution can
significantly lower the Tg and suppress crystallization of these compounds. This resulted in
arylamines that were isolated as liquids, waxes, glasses, and in some cases crystalline solids at
ambient conditions. Additionally, these silyl ether groups were found to be relatively strong
electron donating groups with similar donating potentials to the well-known methyl ether group.
It is concluded that silyl ether substitution is a synthetic handle to greatly alter the physical
properties of arylamines without substantially changing their basic electronic properties.
4.3.2 Introduction
A large number of triarylamine derivatives have been reported and the effects of certain
molecular fragments on the electronic and physical properties of triarylamines are well known.1
However, the vast majority of this effort has been applied to the study of crystalline or glassy
triarylamines. Such materials have very high glass transition temperatures (for solution or
54
54
vacuum deposition of stable amorphous films) or are highly crystalline for applications where a
polycrystalline morphology may be beneficial (OPVs, OFETs).2 On the other hand, there is
comparatively little work appearing in the literature regarding "soft" triarylamines, which we will
define as triarylamines which are liquids or waxes at ambient conditions. There are only two
examples within the literature of arylamine-type compounds that are liquids at room temperature:
tris(4-methoxyethoxyphenyl)amine (TMEPA) and N-(2-ethylhexyl)carbazole (Fig. 4-1).
N
OO
O
O
O
O
N
2-ethylhexyl carbazole
Figure 4-1 Two previously reported liquid arylamines. N-2-ethylhexylcarbazole (left) and
TMEPA (right).
TMEPA is a triarylamine with 2-methoxyethoxy groups in each of the three para-positions. It is a
viscous oil which shows both crystalline and glassy states below room temperature. TMEPA has
been applied in dye sensitized solar cells (DSSCs) showing an efficiency of 2.4% under AM1.5
illumination.3 This is in contrast to the typical use of liquid electrolytes as a hole transporting
medium in DSSCs. Concerns about leakage and long term stability of the liquid electrolyte have
prompted the search for alternatives which has included solid state arylamines.5-9 While TMEPA
shows utility, the synthetic methodology used leaves little room for synthetic control over the
physical and electronic properties through molecular variation.
The second case of a liquid arylamine, N-(2-ethylhexyl) carbazole, is an N-alkylated carbazole.
Carbazoles have been used as building blocks for main chain conducting polymers10 and small
molecule hosts for OLEDs.11 There are several studies exploring the charge transport properties
of N-(2-ethylhexyl)carbazole.12,13 Most importantly, Wada et al. have shown it to have good hole
carrier mobility (greater than poly(N-vinylcarbazole)),14 while Adachi et al. have shown it to
have utility as a liquid host material in OLEDs.15 Once again, this compound shows utility in
several applications but lacks a synthetic handle to tune its electronic and physical properties.
55
55
Given the demonstrated utility of soft arylamines, the development of new materials is necessary
to facilitate further study in this area. Towards this end, the goal of this study was to develop a
simple synthetic methodology which yields liquid, waxy, or low melting triarylamines with
tunable physical and electronic properties. Along with such a methodology, it is also desirable to
use readily accessible molecular fragments which are amenable to assembly via simple and
established chemistry. Silyl ethers where chosen due to their well-defined chemical structures
and because of the unique physical properties of organosilicones.16
4.3.3 Results and Discussion
Initial efforts were focused on simple triarylamines containing one nitrogen-center. A series of
three triarylamines with triisopropylsilyl ether (−OTIPS) substituents in the para position were
prepared. Each is illustrated in Scheme 4-1. The –OTIPS group was chosen initially because of
its hydrolytic stability,17,18 ease of introduction, and its lipophilic structure. Moreover, there is a
consensus that the related –OTIPS groups when added to a conjugated π- electron system by a σ-
bond to carbon is an acceptable functional group for organic electronic materials.19-20 3,4-
Dimethylphenyl substitutes were utilized on the remainder of the triarylamine molecule (in the
case of 4-4a and 4-5) in order to add an additional element of asymmetry and to allow for an
easy comparison of the physical and electronic properties to other triarylamines previously
characterized.21
56
56
NH2
i
HN
OH
Br
OR
Br
N
OR
1 2
2 + 3a-d
Si Si Si SiPh
Ph
3a (R=TIPS)3b (R=TBDMS)3c (R=THDMS)3d (R=DPTBS)
4a (R=TIPS)4b (R=TBDMS)4c (R=THDMS)4d (R=DPTBS)
TIPS = TBDMS = THDMS = DPTBS =
N
OTIPS
OTIPS
LiNH2 + 3a N
OTIPS
OTIPSTIPSO
1 + 3a
5
6
∗ ∗ ∗ ∗
ii
iii
iii
iii
Scheme 4-1: Synthesis of triarylamines containing silyl ethers (Conditions: (i) AlCl3, CaCl2, tetralin, 220 °C. (ii) R-Cl, imidazole, DMF, rt (iii) Pd(OAc)2, P(t-butyl)3, Na(t-butoxide), toluene, 110 °C.).
Our synthetic route to the targeted triarylamines uses p-(triisopropyl)silyloxy bromobenzene (4-
3a) as a simple and basic molecular building block (which was prepared by a known patented
procedure).22 To produce 4-4a, 4-3a was coupled with the diphenylamine derivative 4-2 using
palladium catalyzed Buchwald-Hartwig amination conditions.23-29 Compound 4-2 itself was
4-6
4-5
4-2
4-1
4-1 + 4-3a
4-2 + 4-3a-d
LiNH2 + 4-3a
4-4a (R=TIPS) 4-4b (R=TBDMS) 4-4c (R=THDMS)
4-4d (R=DPTBS)
4-3a (R=TIPS) 4-3b (R=TBDMS) 4-3c (R=THDMS) 4-3d (R=DPTBS)
57
57
synthesized by the self-condensation of 3,4-dimethylaniline (4-1) as adapted from the patented
procedure.30 Compound 4-5 was synthesized using the same amination conditions as for 4-4a
except 3,4-dimethylaniline was used as the starting material. Finally, for triarylamine 4-6,
lithium amide was used as a nitrogen source and was coupled with three equivalents of 4-3a to
form 4-6. In each case, syntheses were performed reliably and reproducibly on the gram and tens
of grams scales.
Table 4-1. Comparison of the physical and electrical properties of compounds 4-4a, 4-5 and 4-6
with previously reported analogous compounds.
Compound R Tg (°C) Tm (°C) E1/2 (mV vs.
Ag/AgCl)
N/A N/A 134a N/A
-OMeb 4 122 735
-OTIPS (4-4a) -14 96 732
-OMeb 1 86 690
-OTIPS (4-5) -28 N/A 692
-OMeb 8 98 654
-OTIPS (4-6) -21 N/A 659
a – Data taken from Goodbrand, H.B. and Hu, N.X. 32
b – Data taken from Bender, T.P. et al. 21 c – Half wave potential measured in acetonitrile by cyclic voltammetry.
Triarylamines 4-4a, 4-5 and 4-6 were characterized by differential scanning calorimetry (DSC)
and cyclic voltammetry (CV) to determine their physical and electronic properties. From DSC
analysis it was found that the inclusion of the –OTIPS group into these compounds significantly
58
58
lowers both the melting point (if present at all) and the Tg when compared to the analogous –
OMe substituted triarylamines (Table 4-1).21,31,32 Compound 4-4a, which is a white solid at room
temperature, was found to exhibit both crystalline and glassy states. In contrast, 4-5 is a room
temperature liquid having a viscosity similar to a PDMS standard with a weight averaged
molecular weight of 79,100 g/mol and a glass transition temperature of −28 °C. Triarylamine 4-6
appears to the eye as a waxy non-flowing solid at room temperature and has a glass transition
temperature of −21 °C. When gently heated with a heat gun, 4-6 begins to flow. Neither 4-5 nor
4-6 showed recrystallization or other phase changes except a Tg during heating or cooling.
Inclusion of the –OMe group has little effect on the physical properties of the resulting
triarylamine26 while inclusion of the –OTIPS group has a marked effect on the physical
properties. For example, the change in melting point from tris(3,4-dimethylphenyl)amine to
bis(3,4-dimethylphenyl)- 4-methoxyphenyl amine is a decrease of 11 °C, whereas from the same
to 4-4a, the melting point is decreased by 37 °C. Cyclic voltammetry measurements show that
each compound undergoes a reversible one-electron oxidation between 600 mV and 700 mV (vs.
Ag/AgCl). This analysis is summarized in Table 4-1. Interestingly, the half wave oxidation
potentials of the three compounds decreases as the number of –OTIPS groups on the triarylamine
are increased. This indicates that the –OTIPS group is electron donating. While it may be
generally understood that silyl ethers are electron donating groups, no direct comparison to
analogous compounds has been made to determine the magnitude of electronic donation into π-
conjugated systems of this type. The electrochemistry of the direct methoxy analogues is
available in the literature.21 A direct comparison between the two sets of molecules reveals that
the –OTIPS group has comparable electron donating ability to the more widely used –OMe
group.
Triarylamines 4-4a, 4-5 and 4-6 all have high solubility in a variety of solvents including non-
polar, aromatic and chlorinated solvents. For example, 4-5 and 4-6 are miscible in chlorinated
solvents (DCM, CHCl3, and chlorobenzenes) as well as common non polar solvents (petroleum
ethers, ethers) and aromatic solvents (toluene, benzene, chlorobenzene). Perhaps somewhat
surprisingly, 4-5 and 4-6 are also practically miscible with hexamethyldisiloxane, silicone fluids
and commercial mixtures of cyclic dimethylsiloxanes. These liquids that are generally not
considered solvents in the field of organic electronics. 4-4a also showed limited solubility in
59
59
hexamethyldisiloxane, solutions up to 4 wt. % could be prepared by gently heating the
triarylamine in hexamethyldisiloxane.
One additional parameter which may be relevant to the application of silyl ether containing
triarylamines is their hydrolytic stability, something which is not an issue with methoxy groups.
Due to their widespread use in protecting group chemistry, other silyl chlorides with a variety of
substituents are readily available and their relative hydrolytic stability is documented. However it
is not known how that knowledge translates to their incorporation into triarylamines. Moreover,
their incorporation may have a different effect on the final physical electronic and physical
properties depending on the structure of the silyl ether.
In order to study these considerations, a series of singly substituted triarylamines with different
silyl ether groups were synthesized. Singly substituted triarylamines were chosen to simplify the
analysis of the hydrolytic stability as only one product would be formed and the hydrolysis
process would be expected to exhibit simple kinetic behaviour (first order). The silyl ethers
chosen for this study were trimethylsiloxy (−OSiMe3), tert-butyldimethylsiloxy (−OSitBuMe2),
tert-hexyldimethylsiloxy (−OSitHexylMe2), and diphenyl-tert-butylsiloxy (−OSitBuPh2) groups.
These different silyl ethers are all commonly used in protecting group chemistry and are known
to span across a range of hydrolytic stabilities.17,18,33 All of the reactions to produce the resulting
triarylamines (4-4b-d, Scheme 4-1) and their intermediates proceeded smoothly except the
coupling of diarylamine 4-2 with the trimethylsilyl ether of 4-bromophenol (not shown). This
reaction did not yield the desired product under a variety of conditions.
Triarylamines 4-4b and 4-4c were isolated as white crystalline powders, similar to 4a in
appearance. DSC analysis shows that 4-4b and 4-4c differ in Tm and Tg with both products
having a higher Tg than 4-4a and a Tm that straddles that of 4-4a. Interestingly, 4-4d was isolated
as a non-crystalline glass which was optically transparent and began to flow upon gentle heating.
DSC analysis showed only a glass transition indicating that this compound forms an amorphous
glass at room temperature. This difference in the observed physical states is likely a consequence
of the larger nature of the –OSitBuPh2 group. Very large aryl substituents are known to increase
the glass transition temperature of triarylamines.34 Finally, comparing the electrochemical data
between the different silyl ether groups, it can be seen that there is little effect on the oxidation
60
60
potential of the compounds. Each compound showed reversible electrochemical oxidation events
that occurred at approximately the same half wave potential as 4-4a (Table 4-2).
Table 4-2. Comparison of the physical and electrical properties of compounds 4-4a-d including hydrolytic stability.
O
N
R
Si Si Si Si
Ph
Ph
TIPS = TBDMS = THDMS = DPTBS =
∗ ∗ ∗ ∗4a 4b 4c 4dR =
Compound Tg (°C) Tm (°C) E1/2 (mV vs. Ag/AgCl)
Acidic Hydrolysis
Halflife (hrs)
Basic Hydrolysis
Halflife (hrs) 4-4a -14a 96a 732 15 260 4-4b 2 86 731 13 34 4-4c -8 100 743 53 200 4-4d 28 N/A 733 770 130
a Repeated from Table 4-1.
In order to evaluate hydrolytic stability a 0.1 mmol solution of each triarylamine (4-4a-d) was
prepared in 95 vol% 1,4-dioxane/5 vol% 1 M HCl or 10 M NaOH aqueous solution. Each sample
was then stirred at room temperature in a sealed vial in the dark and sampled at regular intervals.
It is important to note that the hydrolysis experiments were conducted not as a gauge of real
world stability, but as a metric to confirm expected trends in silyl ether hydrolytic stability. The
triarylamines hydrolyzed exponentially with the expected first order kinetics allowing their half-
lives to be extracted. The results of which are summarized in Table 4-2. Under the acidic test
conditions it was observed that the hydrolytic stability, as measured by the half-life of 4-4a-d,
varies according to: –OSitBuPh2 >> −OSitHexylMe2 > −OTIPS ≈ −OSitBuMe2 and under basic
conditions –OTIPS >> −OSitHexylMe2 > −OSitBuPh2 > −OSitBuMe2. Neither of these trends is
consistent with that which is observed for the analogous phenyl ethers.33 The reason for these
disparities is unclear.
Encouraged by the ability of the –OTIPS group to prevent crystallization and effectively lower
the glass transition temperatures of simple triarylamines, the synthetic strategy was extended to
multi-nitrogen centered arylamines. These molecules typically have higher hole transport
4-4b 4-4c 4-4d 4-4a
61
61
mobilities and more utility in organic electronic devices.2 Taking all of the results outlined above
into account, we felt that the –OTIPS group had the best balance of lowering the Tg and Tm while
maintaining hydrolytic stability. While the very bulky –OSitBuPh2 group prevented
crystallization on the mono substituted triarylamine and possessed good hydrolytic stability, we
were concerned about the relatively high Tg that this group imparted on 4-4d (as compared with
–OTIPS on 4-4a). We believe this would have the effect of raising Tg proportionally if this group
were applied to larger structures as it is has been documented that very bulky substituents on
triarylamine groups can enhance glass formation and raise the Tg value.34
Two well-known classes of two-nitrogen centred arylamines were targeted: those based on the
phenylene diamine (4-7 and 4-8a) and benzidine cores (4-9, 4-10). The synthesis of these
compounds again relied on the use of p-triisopropylsiloxy bromobenzene (4-3a) as a common
reagent (Scheme 4-2). All of these materials with exception of the 4-11 were prepared in a single
step and all were isolated using column chromatography in reasonable yields. Compound 4-11
was prepared in two steps by the selective amination of 4,4`-dibromobiphenyl with excess 3,4-
dimethylaniline followed by further coupling with 4-3a under Buchwald-Hartwig conditions.
62
62
i
NH2
NH2
OTIPS
Br
N N
OTIPS
TIPSO
OTIPS
OTIPS
7
NH2
NH2
OR
Br
N N
RO
RO OR
OR
8a (R = TIPS)8b (R = DPTBS)
i
NH2
NH2
OTIPS
Br
N N
TIPSO
TIPSO OTIPS
OTIPS
9
i
N N
TIPSO OTIPS
11
NHHN
Br
Br
NH3 i
ii
OTIPS
Br
Scheme 4-2 Synthesis of silyl ether containing arylamines with multiple nitrogen centres.
Conditions: (i) Pd(dba)2, P(t-butyl)3, Na(t-butoxide), toluene, 110 °C. (ii) Pd(OAc)2, P(t-butyl)3,
Na(t-butoxide), toluene, 110°C.
4-11
4-9
4-8a (R = TIPS) 4-8b (R = DPTBS)
4-7
63
63
Unlike the triarylamine series, none of the target compounds were isolated as free flowing
liquids at room temperature. Instead it was found that the molecules were either purely
amorphous materials or highly crystalline solids. Both compounds 4-7 and 4-11 formed optically
clear glasses when isolated. Neither of these materials showed crystallization over 2 months
stored at room temperature. DSC analysis only showed glass transitions on heating and cooling,
no other thermal transitions were observed. In contrast, compound 4-9 was isolated as a hard
white powder. DSC showed a melting point upon the first heating cycle at 83 °C. A strong
complementary crystallization peak was observed while the sample was rapidly cooled to −50
°C. Despite this, upon the second heating cycle a weak glass transition was detected at 29 °C,
followed by a melting point at 83 °C. Compound 4-8a was isolated as soft crystalline solid. DSC
did not detect any melting transitions up to 220 °C (the upper limit of our DSC) on the first
heating cycle, while the second heating cycle revealed an endothermic peak at 11 °C. A
complementary exothermic peak at 2 °C was detected on the cooling cycle. Since no thermal
activity was noticed during the first heating scan, which rules out compound degradation, it can
be assumed that this extra set is due to another polymorph of the compound.
The non-crystalline compounds (4-7 and 4-11) both showed excellent solubility in all non-polar
organic solvents. Compound 4-11 was found to be sparingly soluble in hexamethyldisiloxane
while 4-7 was found to be miscible with hexamethyldisiloxane. The crystalline members of this
family (4-8a and 4-9) showed more limited solubility with neither compound being soluble in
hexamethyldisiloxane while remaining soluble in aromatic or chlorinated solvents.
64
64
Table 4-3. Characterization data for multi-nitrogen centred triarylamine series, compounds 4-7,
4-8a-b, 4-9 and 4-11 (see Scheme 4-1 for chemical structures of TIPS and TBDPS).
Compound Tg
(°C)
Tm
(°C)
E1/2 (mV vs
Ag/AgCl)
4-7
N N
OTIPS
TIPSO
OTIPS
OTIPS
23 N/A 702, 986
4-8a
N N
TIPSO
TIPSO OTIPS
OTIPS
N/A 11 421, 868
4-8b
N N
TBDPSO
TBDPSO OTBDPS
OTBDPS
60 159 451, 908
4-9
N N
TIPSO
TIPSO OTIPS
OTIPS
29 83 638, 865
4-11
N N
TIPSO OTIPS
50 N/A 661, 886
65
65
On examination of this series it is observed that the physical properties are strongly symmetry
dependent. Both 4-8a and 4-9 show crystalline domains in the solid state occurring at fairly low
temperatures. While the less symmetric 4-7 and 4-11 form optically transparent glasses upon
heating and cooling. This series demonstrates that the general strategy to use the bulky –OTIPS
group to impede crystallization and impart liquidity fails when moving to larger molecules.
From the experimentation with other silyl ether groups outlined above, it is known that the –
OSitBuPh2 group was sufficiently bulky to disrupt crystallization of a singly substituted
triarylamine (4-4d) while simultaneously having no effect on its oxidation potential. It was
decided to test to see if the –OSitBuPh2 group would be bulky enough to disrupt crystallization
of an analogous compound to the highly crystalline 4-8a. Thus compound 4-8b was synthesized
using a similar synthetic pathway to 4-8a in moderate yield and isolated as small white needles.
CV analysis showed similar electrochemical behaviour as 4-8a while DSC analysis revealed very
complex phase transition behaviour. During the first heating cycle multiple endothermic and
exothermic transitions were observed. Upon the second heating curve only a single glass
transition was found which had a complementarily event on cooling curve. No further
crystallization or melting was observed during the remainder of the analysis. The appearance of a
glass transition temperature during DSC analysis indicates that the use of bulkier silyl ether
substitutes is partially successful at inhibiting crystallization.
4.3.4 Conclusions
In summary, triarylamines functionalized with silyl ethers were synthesized and studied. It was
found that incorporation of –OTIPS group(s) into a triarylamine could drastically lower the glass
transition temperature and inhibit crystallization of the resulting compound. Electrochemical
characterization of these new materials showed that this substitution had a very minor effect on
oxidation behaviour of the compound. When compared to other common silyl ether groups, the –
OTIPS group was found to have the greatest effect on the physical properties of the resulting
material while maintaining moderate hydrolytic stability. When this strategy was extended to
larger multi-nitrogen centered triarylamines, the effect of molecular symmetry was found to be
dominant over the effect of –OTIPS substitution. For less symmetric substitution patterns,
morphologically stable amorphous glasses could be obtained. While for more symmetric
substitution patterns, highly crystalline materials were obtained. These unique triarylamines have
66
66
been made using simple and readily available chemical building blocks and were assembled
using well established chemistry. This study demonstrates the utility of simple silyl ethers in
controlling or altering the physical properties of triarylamines without significantly changing
their useful electronic attributes.
4.3.5 References
1. Thelakkat, M. Macromol. Mater. Eng. 2002, 287, 442–461.
2. Shirota, Y.; Kageyama, H. Chem. Rev. 2007, 107, 953–1010.
3. Snaith, H.J.; Zakeeruddin, S.M.; Wang, Q.; Péechy, P.; Grätzel, M. Nano. Lett. 2006, 6,
2000.
4. Bach, U.; Lupo, D.; Compte, P.; Moser, J.E; Weissörtel, F.; Salbeck, J.; Spreitzer, H.;
Grätzel, M. Nature 1998, 395, 583.
5. Yum, J.; Chen, P.; Grätzel, M.; Nazeeruddin, M.K. Chem. Sus. Chem. 2008, 1, 699.
6. Salbeck, J.; Bauer, J.; Weissörtel, F.; Bestgen, H. Synth. Met. 1997, 91, 209.
7. Snaith, H.J.; Moule, A.J.; Klein, C.; Meerholz, K.; Friend, R.H.; Grätzel, M. Nano. Lett.
2007, 7, 3372.
8. Ding, I-.K.; Tétreault, N.; Brillet, J.; Hardin, B.E.; Smith, E.H.; Rosenthal, S.J.; Sauvage,
F.; Grätzel, M.; McGehee, M.D. Adv. Func. Mater. 2009, 19, 2431.
9. Snaith, H.J., Humphry-Baker, R.; Chen, P.; Cesar, O.; Zakeeruddin, S.M.; Grätzel, M.
Nanotechnology 2008, 424003.
10. Blouin, N.; Leclerc, M. Acc. Chem. Res. 2008, 41, 1110.
11. Brunner, K.; Dijken, A.; Börner, H.; Bastiannsen, J.J.A.M.; Kiggen, N.M.M.; Langeveld,
B.M.W J. Am. Chem. Soc.2004, 126, 6035.
12. Hecdrickx, E.; Guenther, B.D.; Zhang, Y.; Wang, J.F.; Staub, K.; Zhang, W.; Marder,
S.R.; Kippelen, B.; Peyghambarian, N. Chem. Phys. 1999, 245, 407.
13. Ribierre, J.; Aoyama, T.; Kobayashi, T.; Sassa, T.; Muto, T.; Wada, T. J. Appl. Phys.
2007, 102, 033106.
14. Ribierre, J.C.; Aoyama, T.; Muto, T.; Imase, Y.; Wada, T. Org. Electr. 2008, 9, 396.
15. Xu, D.; Adachi, C.; Appl. Phys. Lett. 2009, 95, 053304.
16. Noviadri, I.; Brown, K.N.; Flemings, D.S; Gulyas, P.T.; Lay, P.A.; Masters, A.F.;
Phillips, L. J. Phys. Chem. B 1999, 103, 6713.
67
67
17. Brook, M.A. Silicon in Organic, Organometallic, and Polymer Chemistry, Wiley, New
York, NY, 2000.
18. Wuts, P.G.; Greene, T.W. Greene’s Protective Groups in Organic Synthesis 4th Ed.,
Wiley, Hoboken, NJ, 2007.
19. Anthony, J. Angew. Chem. Int. Ed. 2008, 47, 452.
20. Lehnherr, D.; Gao, J.; Hegmann, F.A.; Tywinsky, R. Org. Lett. 2008, 10, 4779.
21. Bender, T.P.; Graham, J.F.; Duff, J.M.; Chem. Mater. 2001, 13, 4105.
22. Manley, P.J.; Miller, W.H.; Uzinskas, I.N. Vintronectin Receptor Antagonists, European
Patent, 1218005, 2004
23. Hartwig, J.F.; Kawatsura, M.; Hauck, S.I.; Shaughnessy, K.H.; Alcazar Roman, L.M. J.
Org. Chem. 1999, 64, 5575.
24. Jiang, L.; Buchwald, S.L. Palladium-Catalyzed Aromatic Carbon-Nitrogen Bond
Formation, In: de Meijere, A.; Diedereich, F. (Editors) Metal Catalyzed Cross-Coupling
Reactions 2nd
Ed.; Wiley-VCH, NY, 2004
25. Bender, T.P.; Coggan, J.A.; McGuire, G.; Murphy, L.D.; Toth, A.E.J., US Pat. 7408085,
2008.
26. Bender, T.P.; Coggan, J.A. US Pat. 7402700, 2008.
27. Bender, T.P.; Goodbrand, H.B.; Hu, N.X. US Pat. 7402699, 2008.
28. Bender, T.P. Coggan, J.A. US Pat. 7345203, 2008.
29. Coggan, J.A.; Bender, T.P., US Pat. 7332630, 2008.
30. Shintou, T.; Fujii, S.; Kubo, S., US Pat. 6218576, 2001.
31. DSC plots showing temperature heat flow profiles are included in the supporting
information (Section 9.2.2)
32. Goodbrand, H.B.; Hu, N. J. Org. Chem. 1999, 64, 670.
33. Davies, J.S.; Higginbotham, C.L.; Tremeer, E.J.; Brown, C.; Treadgold, R.C. J. Chem.
Soc. Perkin Trans. 1992, 1, 3043.
34. Gagnon, E.; Maris, T.; Weust, J.D. Org. Lett. 2010, 12, 404.
68
68
Chapter 5: Siloxane-Triarylamine Hybrids: Discrete Room Temperature Liquid Triarylamines via the Piers-Rubinsztajn Reaction
5.1 Executive Summary
Sections of this chapter have been published as a letter in Organic Letters as well as a full paper
in the Journal of Organic Chemistry:
Brett A. Kamino, John B. Grande, Mike Brook, Timothy P. Bender (2011), Organic Letters, Vol. 13, No. 1, 154-157. Figure and Schemes are reprinted with permission. Copyright 2011 American Chemical Society This chapter is a conceptual follow up to the work discussed in chapter 4. In chapter 4, the use
of bulky silyl ether groups was found to be ineffective in transforming normally crystalline
triarylamines into liquids at room temperature. One improvement we could think of at the time
was to use oligosiloxanes instead of bulky silyl ether groups. Such oligosiloxanes would have a
great deal more conformational freedom then bulky silyl ethers. And, we hypothesized that this
would be more effective in producing liquid organic semiconductors. Unfortunately, these
groups are somewhat more sensitive to chemical reactions and did not survive the catalytic
coupling reactions used to synthesize triarylamines. In this chapter, we disclose a method where
triarylamines are synthesized with stable –OMe groups and then functionalized with an
oligosiloxane using the Piers-Rubinsztajn chemistry. This unique chemistry is crucial in the
synthesis of these materials and its use on organic functional materials is very novel.
5.2 Statement of Contributions
The authorship of the first paper is as follows: Brett A. Kamino, John B. Grande, Mike Brook,
Timothy P. Bender. All synthesis and characterization was performed by me. John B. Grande
performed initial tests, the results of which were not included in this publication. Mike Brook is
Mr. Grande’s supervisor. The paper was written by me with guidance from Prof. Tim Bender.
69
69
5.3 Paper
5.3.1 Abstract
A series of room temperature liquid siloxane-triarylamine hybrids were synthesized using the
Piers-Rubinsztajn reaction. These materials displayed well behaved electrochemical oxidation
and low Tg’s and were free-flowing liquids. The interaction between the Lewis acidic
tris(pentafluorophenyl)borane catalyst and the Lewis basic starting triarylamine substrates were
investigated by steady state UV-Vis spectroscopy and 19F NMR to reveal a unique and non-
productive charge transfer reaction between substrate and catalyst.
5.3.2 Body
The Piers-Rubinsztajn reaction has been shown to be a powerful way to construct complex
discrete siloxane architectures in an efficient manner.1 This reaction uses the strong Lewis acid
tris(pentafluorophenyl)borane (B(C6F5)3) to catalyze the reaction between Si-H and Si-O-R
groups (where R = H, Me or other alkyl, R3SiH + R′OSiR′′3 → R3SiOSiR′′3 + R′H, Scheme 5-
1A).2 This chemistry typically occurs very rapidly and is done under non-aqueous conditions.
Crucial to the utility of the process is the fact that silicones do not undergo
metathesis/redistribution in the presence of this Lewis acid.1b As well, the borane catalyst is
generally easy to remove and the byproduct is either hydrogen or volatile hydrocarbon gases
(such as methane) either of which rapidly leave the solution during reaction or under gentle
vacuum. Using this chemistry, the synthesis of many complicated and otherwise inaccessible
siloxane structures and other chemical derivatives can be achieved.3
Scheme 5-1: Two synthetic transformations accessible by using the Piers-Rubinsztajn reaction.
70
70
In addition to the synthesis of Si-O-Si bonds for discrete siloxane architectures, this chemistry
has also been shown to work between Si-H bonds and aryl-hydroxyl groups and aryl-methoxy
groups to form aryl-O-Si bonds (Scheme 5-1B).4
In this chapter we describe a series of free-flowing room temperature liquid siloxane-
triarylamine hybrid compounds that were prepared using the Piers-Rubinsztajn reaction. For this
chapter a reactive oligosiloxanes was used: 1,1,1,3,3-pentamethyldisiloxane (-MM). This was
chosen as prototypical reactive silicone because it is a pure and discrete compound, a liquid at
room temperature, inexpensive and readily available.
We begin our study by investigating the use of this chemistry on simple, single nitrogen centered
triarylamines with p-methoxy functionalization. Each precursor p-methoxy-triarylamine can be
synthesized in a single step using well established Buchwald-Hartwig coupling conditions5 by
the reaction between 4-bromoanisole and bis(3,4-dimethylphenyl)amine, 3,4-dimethylaniline, or
p-anisidine giving triarylamines 5-1a-c, respectively. Each methoxy functionalized triarylamine
was subsequently reacted with -MM in the presence of tris(pentafluorophenyl)borane. In a
typical procedure, the triarylamine was dissolved in toluene (10 wt. %) which contained a
catalytic amount of tris(pentafluorophenyl)borane (1 mol. %) at room temperature in an open
vessel. To this, -MM was added drop wise. There is a short induction time following which the
rapid evolution of gas occurs (methane in this case): Safety Note - the evolution can be vigorous,
and the addition rate of the silane should be adjusted accordingly. Reactions were worked up by
the addition of ∼0.5 g of basic alumina, which was allowed to stir for an additional 20 min
within the reaction vessel to capture the borane catalyst. The reaction solution was filtered, and
the solvent and excess 1,1,1,3,3-pentamethyldisiloxane were simply removed by rotary
evaporation. A general reaction is illustrated in Scheme 5-2. The isolated yields for these
reactions typically exceeded 90%. We found that no further purification of these compounds was
required after removal of excess pentamethyldisiloxane and boron catalyst (as shown by HPLC
and 1H/19F NMR analysis). All three siloxane-triarylamine hybrid compounds were isolated as
pale yellow, free-flowing liquids. Compounds 5-2b and 5-2c had viscosities similar to that of a
5130 g/mol weight averaged PDMS standard, whereas 5-2a was similar to a 24 800 g/mol
standard. Precise measurements are underway.
71
71
Scheme 5-2: Synthesis of single nitrogen centered triarylamines 5-2a-c
Each of the compounds 5-2a-c was characterized by differential scanning calorimetry (DSC) to
establish the effect of siloxane substitution on the arylamine and to observe any thermal
transitions which may exist (Table 5-1). DSC analysis was performed by first rapidly cooling
each liquid to -80 °C. Each sample was then subsequently heated to room temperature, back
down to -80 °C and finally back to room temperature all at a rate of 10 °C/min. Sharp glass
transitions (Tg) were observed in all cases in each of the heating cycles. No other thermal
transitions were observed for these compounds. It can be seen that addition of the -MM group
has a strong effect on the physical properties of the triarylamines. The normally crystalline
starting methoxy-triarylamines (5-1a-c) are converted to liquids with very low glass transition
temperatures ranging from -45 to -63 °C. It is observed that increasing the number of -MM
chains decreases the glass transition temperature. In no cases were other thermal transitions
including crystalline transitions observed.
Each siloxane-triarylamine hybrid was also characterized by cyclic voltammetry (CV) to
determine the effect of -MM substitution on the electrochemistry of the compounds. Each was
run under identical conditions to those for compounds 5-1a-c, and their results were compared.6
CV was performed in dichloromethane with (Bu)4NClO4 as a supporting electrolyte. Each
compound was scanned from -300 to +1100 mV and back to -300 mV at 50 mV/s. Each was
cycled through this range four times in total. Decamethylferrocene was used as an internal
standard and all data is corrected to its published half wave potential.7 The results are
summarized in Table 5-1. Siloxane-triarylamine hybrids (5-2a-c) have very similar
electrochemical behavior to that of the methoxy substituted triarylamines 5-1a-c with a single
1a 1b 1c
2a
2b
2c
72
72
reversible oxidation event. We observed that the halfwave oxidation potential (E1/2) for
compounds 5-2a-c decreases with increasing -MM substitution. This implies that -MM is an
electron-donating group.6 However, based on the comparison to the E1/2 for compounds 5-1a-c
we can conclude that the -MM moiety is a weaker electron-donating group than methoxy.
Table 5-1: Thermal and electrochemical information for precursor triarylamine compounds 5-
1a-c and their siloxane functionalized counterparts, 5-2a-c.
The accepted mechanism for the Piers-Rubinsztajn reaction initially involves the formation of a
reversible complex between the Si-H of the silane and the boron center of the Lewis acid catalyst
as a key intermediate step.1b It was anticipated that the strong Lewis acid used herein8 could
competitively bind to the substrate triarylamine, which is a weak Lewis base.9
The efficiency of the process described herein suggests there is little interaction between
tris(pentafluorophenyl)borane and the triarylamine substrate. However, if a single electron
trasnfer interaction took place, it would likely involve the removal of an electron from the
triarylamine resulting in the brightly colored radical cation of the triarylamine thereby allowing
for detection of even trace amounts of interactions.10,11 Thus UV-Vis spectra of triarylamine 5-1c
were taken between 300 and 2000 nm with varying equivalents of tris(pentafluorophenyl)borane
in dilute solutions of toluene (0.0298 mol/L). Looking at the visible region of the spectrum, a
very weak absorbance centered at 742 nm can be observed (Figure 5-1).
73
73
Figure 5-1: Steady-state UV-Vis absorbance spectra of 1c upon additiona of 0.25, 0.5, and 1
equiv. of tris(pentafluorophenyl)borane. Also shown is 1c oxidized with 0.5 equiv. of SbCl5 for
reference.
This peak increased in intensity in a nonlinear fashion with increasing amounts of
tris(pentafluorophenyl) borane. A chemically oxidized solution of triarylamine 5-1c with 0.5
equiv of antimony(V) chloride (SbCl5) was also prepared. It is well-known that the oxidative
action of SbCl5 on a (tri)arylamine produces the radical cation via a single electron transfer.12The
UV-Vis spectrum of the mixture of 5-1c and SbCl5 overlaps with the position and has the same
peak shape observed for the mixtures of 5-1c and tris(pentafluorophenyl)borane (Figure 5-1). It
can thus be concluded that there is some level of interaction between
tris(pentafluorophenyl)borane and the triarylamine and that the interaction results in the
formation of a radical cation/radical anion pair. The absorbance at 742 nm was extremely weak
compared to its primary absorption band at 298 nm. Given the extinction coefficient of a
(tri)arylamine radical cation is known to be very high13 relative to the neutral compound, the
spectra suggest that 5-1c and tris(pentafluorophenyl)borane are in an equilibrium shifted far
toward dissociation. To confirm this, 19F NMR was performed on an equimolar mixture of 5-1c
and tris(pentafluorophenyl)borane. No change in the 19F chemical shifts of
tris(pentafluorophenyl)borane was observed thereby confirming the equilibrium is shifted far
toward dissociation.
74
74
In summation, the functionalization of triarylamines with discrete siloxane chains under Piers-
Rubinsztajn conditions (tris(pentafluorophenyl)borane catalysis) has been shown to drastically
change their physical properties. The result is a sample of three free-flowing room temperature
liquid siloxane-triarylamine hybrids. Any Lewis acid/Lewis base interaction between the
arylamine and borane catalyst is weak such that free catalyst is available to interact with the
hydrosilane and initiate the Piers-Rubinsztajn process. We believe that this synthetic strategy
will facilitate further application of liquid arylamines in optoelectronic devices.
5.3.3 References
1. (a) Grande, J. B.; Thompson, D. B.; Gonzaga, F.; Brook, M. A. Chem. Commun. 2010,
46, 4988. (b) Brook, M. A.; Grand, J. B.; Ganachaud, F. Adv. Polym. Sci. 2010, 1.
2. (a) Piers, W. E. The Chemistry of Perfluoroaryl Boranes. In Advances in Organometallic
Chemistry; West, R., Hill, A. F., Eds.; Elsevier Academic Press: San Diego, 2005; Vol.
52, 1. (b) Chojnowski, J.; Rubinsztajn, S.; Cella, J. A.; Fortuniak, W.; Cypryk, M.;
Kurjata, J.; Kazmierski, K. Organometallics 2005, 24, 6077.
3. Thompson, D. B.; Brook, M. A. J. Am. Chem. Soc. 2008, 130, 32.
4. Cella, J.; Rubinsztajn, S. Macromolecules 2008, 41, 6965.
5. (a) Hartwig, J. F.; Kawatsura, M.; Hauck, S. I.; Shaughnessy, K. H.; Alcazar Roman, L.
M. J. Org. Chem. 1999, 64, 5575. (b) Jiang, L.; Buchwald, S. L. Palladium-Catalyzed
Aromatic Carbon-Nitrogen Bond Formation. Metal-Catalyzed Cross-Coupling Reactions,
2nd ed.; de Meijere, A., Diederich, F., Eds.; Wiley-VCH: 2004; Chapter 13. (c) Bender,
T. P.; Coggan, J. A.; McGuire, G.; Murphy, L. D.; Toth, A. E. J. US Patent 7,408,085,
2008. (d) Bender, T. P.; Coggan, J. A. US Patent 7,402,700, 2008. (e) Bender, T. P.;
Goodbrand, H. B.; Hu, N. X.; US Patent 7,402,699, 2008. (f) Bender, T. P.; Coggan, J.
A.; US Patent 7,345,203, 2008. (g) Coggan, J. A.; Bender, T. P. US Patent 7,332,630,
2008.
6. Bender, T. P.; Graham, J. F.; Duff, J. M. Chem. Mater. 2001, 13, 4105
7. Noviandri, I.; Brown, K. N.; Fleming, D. S.; Gulyas, P. T.; Lay, P. A.; Masters, A. F.;
Phillips, L. J. Phys. Chem. B 1999, 103, 6713.
8. Brook, M. A. Silicon in Organic, Organometallic, and Polymer Chemistry; John Wiley &
Sons, Inc.: New York, 2000.
9. Piers, W. E.; Chivers, T. Chem. Soc. Rev. 1997, 26, 345.
75
75
10. Park, M. H.; Park, J. H.; Do, Y.; Lee, M. H. Polymer 2010, 51, 4735.
11. Blackwell, J. M.; Sonmer, E. R.; Scoccitti, T.; Piers, W. E. Org. Lett. 2000, 2, 3921.
12. Amthor, S.; Noller, B.; Lambert, C. Chem. Phys. 2005, 316, 141–152.
13. Zhou, G.; Baumbarten, M.; Müllen, K. J. Am. Chem. Soc. 2007, 129, 12211.
76
76
Chapter 6: Liquid Triarylamines: The Scope and Limitations of Piers-Rubsinsztajn Conditions for Obtaining Triarylamine-Siloxane Hybrid Materials
6.1 Executive Summary
This chapter was published as a full paper in the Journal of Organic Chemistry.
Brett A. Kamino, Bridget Mills, Christopher Reali, Michael J. Gretton, Mike Brook, Timothy P.
Bender, 2012, Journal of Organic Chemistry, 77 (4), 1663-1674.
Figure and Schemes are reprinted with permission. Copyright 2011 American Chemical Society
This paper is a follow up publication to Chapter 6 where the previously mentioned concepts are
greatly expanded on. Because of the success of our synthetic strategy for producing liquid
organic semiconductors, we sought to expand our prior work and determine the limits of this
particular strategy for obtaining liquid semiconductors. As well, there was a strong desire to
explore the nature of the catalyst substrate interactions found in the previous chapter.
In this study, we attempted to produce liquid versions of a large range of nitrogen containing
hole transport materials found across the literature. This was done to show the utility of our
methodology as well as to build up a library of potential compounds to study in device
applications. This study was fairly successful and we were able to produce liquid versions of a
large number of organic semiconductors while learning a number of key molecular design rules.
In concluding this study and the previous one, I can safely say that we have extensively
demonstrated a flexible strategy to easily produce liquid organic semiconductors.
6.2 Statement of Contributions
The author list for this paper is as follows: Brett A. Kamino, Bridget Mills, Christopher Reali,
Michael J. Gretton, Mike Brook, Timothy P. Bender. Bridget Mills and Christopher Reali were
undergraduate students working under me on this project. They contributed towards the synthesis
of chemical intermediates and several of the final products using procedures developed by me.
77
77
Michael J. Gretton provided input on the project. Mike Brook originally consulted on the use of
Piers-Rubinsztajn chemistry for triarylamines. The large bulk of synthesis was performed by me.
As well, all characterization and studies into catalyst interaction was performed by me. The
paper was written by me with input from Prof. Bender.
6.3 Paper
6.3.1 Abstract
New liquid triarylamine−siloxane hybrid materials are produced using the Piers−Rubinsztajn
reaction. Under mild conditions, liquid analogues of conventional and commonly crystalline
triarylamines are easily synthesized from readily available or accessible intermediates. Using a
diverse selection of triarylamines, we explored the effects of siloxane group and substitution
pattern on the physical properties of these materials, and we have demonstrated that relatively
large molecular liquids with desirable electrochemical properties can be produced. The
interactions between the strongly Lewis acidic catalyst used for this transformation,
tris(pentafluorophenyl)borane (BCF), and the Lewis basic triarylamine substrates were studied.
Through UV−vis−NIR and 19F NMR spectroscopy, we have proposed that the catalyst undergoes
a reversible redox reaction with the substrates to produce a charge transfer complex. The
formation of this charge transfer complex is sensitive to the oxidation potential of the
triarylamine and can greatly affect the kinetics of the Piers−Rubinsztajn reaction.
6.3.2 Introduction
We have recently shown that the incorporation of short, discrete disiloxane units around the
periphery of triarylamines is a versatile strategy to produce liquid triarylamines (see Chapter 5).
Central to this synthetic strategy is the use of the Piers−Rubinsztajn reaction,1 which uses
tris(pentafluorophenyl)borane (BCF) as a catalyst) to activate stable and easily handled silanes.
The reaction is performed under very mild and ambient conditions and requires low catalyst
loadings. The only byproduct of the reaction is methane, and the substitution proceeds without
metathesis or redistribution of the siloxane component, which commonly occur for many types
of siloxane chemistries and limit the ability to construct discrete structures. Rapid conversion
was observed despite the use of the strongly Lewis acidic catalyst, which on first examination
may have been assumed to complex with the Lewis basic triarylamine substrate,2 preventing the
78
78
reaction from proceeding. An investigation using UV−Vis spectroscopy into the potential
complexation showed a small amount of charge transfer between BCF and the triarylamine
indicated by the presence of an absorption, which could be directly attributed to the oxidized
arylamine (radical cation). Despite the detectable presence of this absorption, the relatively weak
signal observed coupled with the known high extinction coefficient for radical cations of
triarylamines suggests that the equilibrium between the charge transfer state and the neutral state
lies far toward the latter.
Piers−Rubinsztajn conditions have previously been shown to enable the reaction of silanes with a
number of different coupling partners including carbonyl groups,3 aryl hydroxyl/alkoxy groups,4
alkyl hydroxyl groups,5 siloxy groups, and silanols.6 Piers−Rubinsztajn conditions have been
shown to have a wide scope and have been used for the synthesis of structured and functional
materials such as siloxane dendrimers,7 polysiloxanes and copolymers thereof,8 and surface
active siloxane ambiphiles.9 While this chemistry has good functional group tolerance,10 there
are cases where Lewis basic substrates react poorly because of competitive catalyst binding to
these Lewis basic functionalities.11 The strength of the Lewis basic functionality is thus an
important factor in the reaction kinetics and whether the reaction can proceed at all.
Our original study (Chapter 5) was limited to performing this reaction on simple triarylamines
with a single nitrogen center. However, simple triarylamines have a limited range of
electrochemical oxidation potentials and applications in functional devices.12 Therefore, we
sought out to broaden the scope of the Piers−Rubinsztajn process and its intersection with
triarylamine−siloxane hybrid materials with an aim at producing a larger number of liquid
triarylamines. We have focused our attention on multinitrogen centered triarylamines as well as
molecules containing the related carbazole moeity. Triarylamines containing multiple conjugated
nitrogen centers are known to possess a wider range of electrochemical properties and can
exhibit better stability upon oxidation (see Chapter 3), leading to improved device performance.
Conversely, they also have the potential to be significantly more Lewis basic than simple
triarylamines because of their multiple nitrogen centers. Therefore, these substrates provide an
opportunity to probe the scope and limitation of the reaction of methoxy-functionalized
triarylamines with discrete silanes under Piers−Rubinsztajn conditions. The limitation of most
interest is whether the decrease in oxidation potential on moving to triarylamines with multiple
79
79
centers will result in a significant shift in charge transfer equilibrium between BCF and the
triarylamine substrate, thus inhibiting the reaction.
6.3.3 Results and Discussion
While there are many different triarylamine structures from which to choose for this study, we
began by choosing two of the more common motifs: triarylamines with a phenylene diamine core
and those with a benzidine core (Scheme 6-1). Several variants on these backbones were
synthesized so as to understand the effect of molecular symmetry and degree of siloxane
functionalization on the physical and electrochemical properties of the resulting materials.
Furthermore, the structural changes in each variant are also accompanied by inherent electronic
variations affecting the Lewis basicity of the molecule.
Triarylamines based on a phenylene diamine core (compounds 6-2a−b) were synthesized in two
steps (Scheme 6-1). 1,4-Phenylene diamine was first reacted with 4-bromoanisole under standard
Buchwald−Hartwig amination conditions13 to yield an intermediate triarylamine 6-1. This aryl-
methoxy-substituted triarylamine was then functionalized with discrete siloxane groups
(1,1,1,3,3-pentamethyldisiloxane (MMH) or 1,1,1,3,5,5,5-heptamethyltrisiloxane (MDHM)) by a
reaction with the corresponding silanes in the presence of a catalytic amount of
tris(pentafluorophenyl)borane (BCF, the so-called Piers−Rubinsztajn conditions) under ambient
and open air conditions. In our previous work (Chapter 5), we found that the functionalization of
methoxy-containing triarylamines with MMH under these conditions proceeded rapidly.
However, in this case, complete conversion took approximately 7 h to achieve. Gentle heating
(50 °C) was found to speed up the process considerably. Caution: As the temperature in the flask
increased, the reaction would proceed rapidly with the rapid evolution of methane gas.
80
80
NH2H2N
OMe
Br
Pd(dba)2P(t-butyl)3Na(t-butoxide)
toluene, reflux
NN
MeO
MeO OMe
OMe
B(C6F5)3
toluene, 50 oC
MMH or MDHM
NN
R
R R
R
6-1 6-2a R = -OMM
6-2b R = -OD(M)2
NH2
R1
R2
MeO
Br
Pd(dba)2P(t-butyl)3Na(t-butoxide)
toluene, reflux
HN
R1
R2
OMe
6-3a R1 = -H, R2 = -H
6-3b R1 = -CH3, R2 = -H
6-3c R1 = -CH3, R2 = -CH3
Pd(OAc)2P(t-butyl)3Na(t-butoxide)
toluene, reflux
Br Br
N N
R1R2R1 R2
MeO OMe
B(C6F5)3toluene, rt
MMH or MDHM
6-4a R1 = -H, R2 = -H
6-4b R1 = -CH3, R2 = -H
6-4c R1 = -CH3, R2 = -CH36-4d R1 = -OMe, R2 = -H
N N
R1R2R1 R2
R3 R3
6-5a R1 = -H, R2 = -H, R3 = -OMM
6-5b R1 = -CH3, R2 = -H, R3 = -OMM
6-5c R1 = -CH3, R2 = -CH3, R3 = -OMM
6-5d R1 = -OMM, R2 = -H, R3 = -OMM
6-5e R1 = -CH3, R2 = -H, R3 = -OD(M)26-5f R1 = -OD(M)2, R2 = -H, R3 = -OD(M)2
Scheme 6-1: Synthesis of siloxane functionalized arylamines.
Triarylamines with a benzidine core (6-5a−h) were synthesized in three steps (Scheme 1).
Diarylamines were first prepared by Buchwald−Hartwig coupling of the corresponding aryl
bromides with an excess of the appropriate aniline. In our case, each diarylamine was easily
81
81
purified by an acidic aqueous extraction followed by recrystallization from nonpolar solvents.
They were then reacted with 4,4′-dibromobiphenyl to achieve the methoxy-functionalized
triarylamines (6-4a−e). Finally, the triarylamines were functionalized with discrete siloxane
chains by reaction with the corresponding silane and catalytic amounts of BCF to give
compounds 6-5a−h. Unlike the reaction with the 1,4-phenylene-based materials (6-2a−b), the
introduction of the siloxane groups proceeded quickly at room temperature, requiring up to a
minute of induction time before reacting rapidly.
Generally speaking, all reactions proceeded to high conversion, and we did not see any
correlation between triarylamine molecular structure and crude yields. We also did not see a
correlation between the equivalent amount of silane used (in some cases we used 2 equiv. and in
others 5 equiv.) and the crude yields. NMR analysis of the crude reaction mixtures does suggest
that the reaction generates small amounts of polymeric silicone species as evidenced by a
corresponding and characteristic CH3 resonance in the 1H NMR spectrum. The generation of this
byproduct is likely due to the reaction of ambient water with silane in the reaction mixture
moderated by BCF.14 Column chromatography was found to be effective in removing this
byproduct. Clearly, conducting the P−R process under anhydrous conditions would preclude the
formation of the silicone species. However, as column chromatography is generally necessary to
produce triarylamine suitable for study in organic electronic devices, its use to remove the
produced silicones is balanced against the ease of operating under ambient vs. anhydrous
conditions.
All of the final triarylamine−siloxane hybrid materials were isolated by column chromatography
(SiO2, toluene/cyclohexane) as viscous liquids (compounds 6-2b, 6-5a−c, e−f,h) or as crystalline
solids (compounds 6-2a, 6-5d, and 6-5g), and their structure and purity (and those of the
intermediates) were unambiguously confirmed by high resolution mass spectrometry (HRMS)
and NMR analysis. Yields for the complete unoptimized process ranged significantly between 48
and 90% after column chromatography. Overall, compounds with the bulkier −OD(M)2 group
gave higher isolated yields than those with the less bulky −OMM group.
Each compound was characterized by differential scanning calorimetry (DSC) to determine the
effect of silicone substitution and molecular symmetry on the melting point and/or glass
transition temperatures of the materials (Table 6-1). Consistent with our observations regarding
82
82
the analogous single nitrogen centered triarylamine−siloxane hybrids (Chapter 5), adding
discrete silicone groups to the arylamine cores had a significant effect on the glass transition
temperature (Tg) and the presence of a crystalline state. Using pentamethyldisiloxane (−OMM)
as a siloxane, the most symmetrically substituted arylamines (6-2b,6-5d, 6-5g) were isolated as
crystalline solids and exhibited well-defined and sharp melting points by DSC. Upon heating,
compound 6-5d exhibited two exothermic transitions at 52 and 58 °C, possibly indicating
polymorphism. For each compound that showed a melting transition on the first DSC scan, a
glass transition temperature well below room temperature was detected on the second heating
cycle. These low glass transition temperatures suggested that if crystallization could be inhibited,
the materials would behave as liquids at room temperature. This hypothesis was tested by
utilizing the bulkier and branched 1,1,1,3,5,5,5-heptamethyltrisiloxane (−OD(M)2) group in
place of the linear –OMM group. The resulting compounds (6-2b, 6-5f, 6-5h) were isolated as
free-flowing oils, and no detectable crystallization was observed over several months of storage
at ambient conditions. The bulkier siloxane groups appear to prevent the π−π stacking
interactions that are found in the crystal structures of these molecules.15 Additionally, we found
that the presence of asymmetry in the substitution pattern of the triarylamine along the axis
bisecting the two nitrogen atoms resulted in compounds that were isolated as highly viscous oils
at room temperature (6-5a, 6-5b, 6-5c, 6-5e). For example, compounds 6-5a−c containing two
−OMM groups and various methyl group substituents on the adjacent phenyl ring are liquids,
whereas their symmetric counterparts are not. Increasing the number of methyl groups raised the
glass transition temperature, whereas replacing the linear −OMM siloxane with a branched
−OD(M)2 siloxane (6-5e) lowered the glass transition temperature by 15 °C as compared to its
structural counterpart (6-5b).
83
83
Table 6-1: DSC and CV results from silicone-hybridized triarylamines.
Compound Appearance Tm (0C) Tg (0C)
Eox 1 (mV vs.
Ag/AgCl)
Eox 2 (mV vs.
Ag/AgCl)
6-2a Crystalline 87 -49§ 443 902
6-2b Oil - -47 436 906
6-5a Oil - 6 749 994
6-5b Oil - 11 725 942
6-5c Oil - 14 673 935
6-5d Crystalline 52, 58 -23§ 661 892
6-5e Oil - -4 699 942
6-5f Oil - -31 682 921
6-5g Crystalline 88 -1 701 907
6-5h Oil - -9 704 929
6-9 Crystalline 150 28 616 772
6-11 Crystalline 131 20 366 696
6-15a Oil - -44 1495 † -
6-15b Oil - -50 1320 † -
6-15c Crystal 47 -48§ 1485 † -
6-15d Oil - -48 1510 † -
§ - detected on second heating cycle. † - Irreversible, peak potential on first scan reported. Tm – melting temperature; Tg – glass transition temperature; Eox,1 – first half wave oxidation
potential; Eox2 – second half wave oxidation potential.
84
84
From these observations, along with those in the previous chapter, we can make several
conclusions about the effect of siloxane substitution on the physical state of arylamines. We find
that the incorporation of larger siloxane chains lowers the glass transition temperature of the
material. Furthermore, as the base molecule increases in size, the number of siloxane chains
needed to achieve a room temperature liquid arylamine−silicone hybrid increases. A secondary
consideration is the addition of asymmetry to the molecule, which is shown to decrease the
chances of crystallization in the molecule.
The electrochemical behavior of this initial group of triarylamine−siloxane hybrids was studied
using solution cyclic voltammetry in dichloromethane with 0.1 M tetrabutylammonium
perchlorate as a supporting electrolyte. A small amount of decamethylferrocene was added to all
solutions and used as an internal standard.16 The results of the electrochemical analysis are
included in Table 6-1. All of the compounds underwent two reversible 1-electron oxidation
events, which is characteristic of triarylamines containing two nitrogen centers. This
demonstrates that the siloxane functionalization of arylamines does not have an undesirable
impact on their electrochemical behavior. Variations in the position of the oxidation potentials
can be explained by number and strength of electron-donating silicone groups as well as degree
of conjugation between each arylamine redox center. There does not seem to be a consistent
difference in the electron-donating potential of the −OD(M2) versus the −OMM group.
Encouraged by the success of this chemistry on phenylenediamine and benzidine-based
substrates, we further extended this study to larger (higher molecular weight) multinitrogen
centered triarylamines. Two well-known triarylamine structures were chosen as model
compounds: one based on the spiro-TAD core17 and one based on the TDATA motif, each
containing four nitrogen centers (Schemes 6-2 and 6-3, respectively). The spiro-TAD derivative
(6-9) was synthesized using a slightly modified literature procedure,18 resulting in a structure
containing four aryl-methoxy groups for substitution (Scheme 6-2). When reacted with MDHM
under the Piers−Rubinsztajn conditions, the substrate reacted rapidly and cleanly to yield a
molecular glass upon isolation, which ultimately crystallized over several weeks. The TDATA
structure (6-11) was synthesized in two steps from tris(p-bromophenyl) amine (Scheme 6-3) and
isolated as a crystalline solid. In this case, the reaction proceeded very slowly requiring
approximately 16 h for completion. Both structures showed typical electrochemical behavior
85
85
relative to their respective classes, and their synthesis demonstrates the ability of
Piers−Rubinsztajn conditions to successfully install −OD(M)2 units on large multi-nitrogen
centered substrates.
Br
O1) MgTHF
2)
3) HClAcetic Acid
Br2/FeCl3DCM, rt
Br
Br
Br
Br
HN
OMe
Pd(OAc)2P(t-butyl)3Na(t-butoxide)
Toluene, reflux
N
N
N
N
O
O
O
O
Si
Si
Si
Si
O
O
O
O
OO
OO
Si
Si
Si
Si
Si
Si
Si
Si
NN
NN
OMe
MeOOMe
OMe
B(C6F5)3Toluene, rt
MDHM
6-6 6-7
6-86-9
Scheme 6-2: Synthesis of spiro core triarylamine 6-9
Scheme 6-3: Synthesis of triarylamine 6-11
86
86
Next, we chose to extend this chemistry to a related group of arylamine semiconductors:
carbazoles. To this end, a number of N-phenylcarbazoles with methoxy-substituents in various
positions were synthesized and subjected to the Piers−Rubinsztajn reaction conditions.
Carbazoles, like triarylamines, are common materials in organic electronics and have been used
as both p-type semiconductors and ambipolar host materials.19 Four N-phenylcarbazole
precursors were synthesized. For the structures with methoxy groups present on the carbazole
ring itself (6-14a−b, Scheme 6-4), Suzuki coupling of 1-bromo-2-nitro-4-methoxybenzene and
an arylhalide followed by a reductive ring-closing reaction promoted by triethylphosphite
resulted in the desired carbazoles (6-13a−b). These carbazoles were then N-arylated under
Ullman coupling conditions to yield the final methoxy-functionalized precursors (6-14a−b), of
which 6-14b has been previously described. Those with methoxy groups on the phenyl ring (6-
14c−d) were prepared in a one-step procedure under Ullman coupling conditions using carbazole
and the appropriate halo-anisole. Because of the planar molecular structure of compounds 6-
14a−d, they were further functionalized exclusively with −OD(M)2 groups under
Piers−Rubinsztajn conditions in order to inhibit any possible crystallization. In each case, the
reaction proceeded extremely rapidly, and the resulting siloxane-functionalized carbazoles (6-
15a−d) were isolated in good yields. For all but compound 6-15d, the resulting materials were
isolated as clear free-flowing liquids. Electrochemical analysis of the carbazoles 6-15a−d
showed that each underwent an irreversible one electron oxidation typical for carbazoles.19
Interestingly, the di-substituted 6-14b appears to undergo two oxidations, which are poorly
resolved under standard cyclic voltammetry conditions. It is unclear at this time whether these
events represent two subsequent electrons being removed or that another chemical change is
occurring. Full electrochemical and calorimetry data for these compounds is included in Table 6-
1. The effect of substitution pattern on the physical properties of the carbazoles is in line with our
previous observations in that the most symmetric substitution patterns (6-15d) result in a
derivative that was crystalline, whereas the asymmetrically substituted structures are isolated as
liquids.
87
87
Scheme 6-2: Synthesis of siloxane functionalized carbazoles.
Effect of Substrate on Catalyst Efficacy. In our approach to the synthesis of
arylamine−siloxane hybrid materials, the use of Piers−Rubinsztajn conditions is critical to the
installation of discrete siloxane groups while avoiding unwanted metathesis and redistribution
reactions of the silicones. The previously studied simple triarylamines were found to react
rapidly at room temperature (often reacting as quickly as silane could be added to the mixture).
However, in this study, it was observed that the efficacy of this reaction (as indicated by its time
to completion at room temperature) varied depending on the structure of the triarylamine
substrate. The rate of the reaction for this series of compounds could be qualitatively observed by
the evolution of methane gas. Compared to the triarylamines used in our previous study, the
benzidine-based substrates reacted somewhat more slowly, with reactions typically finishing
several minutes after complete silane addition. Substrates 6-1 and 6-10 stood out as the only
substrates requiring heat to proceed rapidly; leaving the substrates to react at room temperature
necessitated 7 and 16 h of reaction time for complete substitution, respectively. We also
observed rapid reaction in the formation of triarylamines 6-9 and 6-11 and also for all carbazole
derivatives (6-14a−d).
In our previous work, we found an interaction between the strongly Lewis acidic
tris(pentafluorophenyl)borane (BCF) and the weakly Lewis basic tris(p-methoxyphenyl)amine
did occur but that the level of interaction was quite weak. This interaction between catalyst and
substrate was shown to result in the formation of the triarylamine radical cation. However, we
88
88
did not directly prove the existence of the corresponding radical anion of BCF. While such
reactions are uncommon, several examples of BCF acting as an oxidant are noted in the
literature.20 A complete understanding of the strength of BCF as an oxidant has not been
established owing to the instability of the this particular borane anion.21 Since the radical cation
of an arylamine can be easily detected by its characteristic UV−vis−NIR absorption, we set out
to see if the observed differences in reactivity between triarylamines could be explained by
differing interactions between the precursor and the BCF catalyst.
Solutions of arylamines 6-1 and 6-4d were prepared in toluene (our reaction solvent) along with
varying molar equivalents of BCF. Compounds 6-1 and 6-4d were chosen as representative
compounds because their oxidized cations have been previously studied in the literature.22
Furthermore, the observed reaction kinetics with these substrates varied greatly under the
described conditions. To study this interaction under simulated reaction conditions, solutions of
both BCF and substrate were prepared under ambient conditions and allowed to stand in open air
for 15 min. These solutions were studied by UV−Vis−NIR absorbance measurements, which
found large changes in the visible and near-infrared region of the spectra upon addition of BCF
(see Figure 6-1). Compounds 6-1 and 6-4d both exhibited broad absorption bands in the NIR as
increasing amounts of BCF were added. These broad absorption bands can be assigned to
intervalence charge transfer (IVCT) bands of the radical cations of the arylamines (6-1•+ and 6-
4d•+, respectively), which result from the partial delocalization of the charge between two
conjugated redox centers. The UV−Vis−NIR absorbance spectra of 6-1•+ and 6-4d•+ are well-
studied as model charge transfer systems, and their molar extinction coefficients in
dichloromethane are known.22 A comparison between the published spectra of 6-1•+ and 6-4d•+
and the spectra generated by mixing the neutral triarylamines with BCF reveals that they are
practically the same. Small differences in the λmax found in the literature and in our study are
likely due to differences in the solvents used for each measurement. Such charge transfer bands
are inherently sensitive to solvent polarity.23 The presence of atmospheric conditions can
potentially complicate this experiment, as it is well-known that BCF readily forms adducts with
water under the conditions of this study.24 To rule out any possibility of water playing a role in
the observed reaction, solutions were prepared under glovebox conditions. Under these
anhydrous conditions, the exact same color changes were noted, and the samples were
spectroscopically identical.
89
89
Figure 6-1: Steady-state solution absorbance spectroscopy in toluene of a) compound 6-1 b) compound 6-4d with 0, 0.25, 0.5, and 1 equivalents of BCF. Arrows indicate increasing absorption with increasing equivalents of BCF.
On the basis of these spectra and the known molar extinction coefficients of 6-1•+ and 6-4d•+
(albeit in different solvents) we can estimate the amount of arylamine that is oxidized (see tables
S6-1 and S6-2). If an equimolar mixture of 6-1 and BCF is considered, the percentage of 6-1
oxidized is 5 mol % (corresponding to 5 mol % BCF reduced). If the same consideration is given
to a mixture of 6-1 with catalytic amounts of BCF (0.01 equiv to 6-1), the amount of 6-1
oxidized is 0.2 mol % (corresponding to 20 mol % of BCF reduced). In a similar manner for
90
90
compound 6-4d, 2 mol % is oxidized at equal molar amounts (corresponding to 2 mol % BCF
reduced), and 0.03 mol % is oxidized at catalytic amounts (corresponding to 3 mol % BCF
reduced). We can therefore conclude that while the presence of 6-1•+ and 6-4d•+ is detectable,
even by eye, the result is not the quantitative reduction of BCF to BCF•−, rather it is only a partial
reduction. Furthermore, given the partial reduction and the absence of the formation of a
precipitate,25 we hypothesize that the system is in a dynamic equilibrium between the charge
transfer couple and the freely dissociated species. Taking into consideration our previous
observation of the very slight oxidation of tris(p-methoxyphenyl)amine by BCF, we propose that
the extent of oxidation of the arylamine by BCF is directly related to the oxidation potential of
the arylamine. That is, the equilibrium shifts toward formation of the radical cation/radical anion
pair for arylamines with lower oxidation potentials. The oxidation potentials of the tris(p-
methoxyphenyl)amine, 6-4d, and 6-1 are 654,26 605,22 and 375 mV vs. Ag/AgCl, respectively.
Additionally, these values are proportional to the observed kinetic rates of the substrates under
these conditions. This result suggests that the nature of interaction between triarylamines and
BCF is a redox reaction where the BCF is acting as an oxidant. Furthermore, we can conclude
that the redox reaction between certain triarylamines and BCF results in partial sequestration of
the catalyst and retardation of the rate of the desired reaction.
To further support this hypothesis, mixtures of 6-1 and 6-4d along with 1 mol % equiv of BCF
were dissolved in toluene-d8 and studied by 19F and 1H NMR. In each case, the 1H spectra
obtained were significantly broadened because of the presence of the paramagnetic arylamine
radical cation (see section 12.4, Figures S6-3 and S6-5). 19F NMR spectra were difficult to obtain
with a reasonable signal-to-noise ratio because of the highly dilute nature the BCF and the
relatively low solubility of arylamines 6-1 and 6-4d. The 19F NMR of the mixture of compound
6-1 and 1 mol % BCF displayed a large number of resonances, with several corresponding to the
free BCF (Section 12.4, Figure S6-2). Under the same conditions, the mixture of compound 6-4d
and 1 mol % BCF resulted in a cleaner spectrum comprising mostly of free BCF (Section 12.4,
Figure S6-4). Because of the poor signal-to-noise ratio obtained and the paramagnetic nature of
the solution, concrete comparisons between the amount of free BCF in solution in the
UV−Vis−NIR experiment and the NMR experiment are difficult to make.
91
91
We therefore considered mixtures of arylamines 6-1 and 6-4d and BCF in a 1:1 molar ratio (in
C6D6; Section 12-4, Figures S6-6 and S6-7). Under these conditions, all three fluorine resonances
of the free BCF are visible and make up the majority of the detected signal, although moderately
broadened. This was particularly evident for compound 6-1, and the difference in observed
amount of free BCF between the two concentrations supports the idea of a dynamic chemical
equilibrium between the free and bound state.
6.3.4 Conclusions
In summary, the scope and limitations of Piers−Rubinsztajn conditions for the synthesis of
silicone−arylamine hybrids has been explored with an emphasis on obtaining liquid triarylamines
having multiple nitrogen centers. The catalytic functionalization of a series of two nitrogen
centered triarylamines was successful, and this substitution was found to have a significant effect
on the physical properties of the arylamines, resulting in a number of new liquid triarylamines.
We observed that by using the bulkier and branched −OD(M)2 group, normally crystalline bis-
arylamines could be made into free-flowing liquids by effectively lowering the glass transition
temperature to below room temperature and inhibiting crystallization. The flexibility of this
synthetic strategy was further explored by demonstrating that this chemistry can be used on
larger multinitrogen centered arylamines as well as on carbazole-based precursors. The siloxane-
functionalized triarylamines retained the electrochemical behavior of their parent compounds.
Furthermore, the interaction between the Lewis acidic BCF (tris(pentafluorophenyl)borane) and
the Lewis basic arylamine was further studied. It is proposed that the BCF catalyst can act as a
one-electron oxidant, forming a radical cation/radical anion pair that is in equilibrium with the
freely dissociated arylamine and BCF. This redox reaction sequesters the catalyst and retards the
rate of the desired reaction in some cases. This mechanism is supported by UV−vis−NIR and 19F
NMR spectra. From studying these compounds, we hypothesize that the extent of the charge
transfer interaction is dependent on the triarylamine oxidation potential. More easily oxidized
triarylamines appear to achieve an equilibrium state further favoring the charge transfer pair than
those triarylamines that are more electron-poor. This observation directly relates to the
qualitative kinetics of the Piers−Rubinsztajn reaction on these substrates.
Through the work presented in both our preliminary study and this one, we have successfully
increased the number of known liquid organic semiconductors. These novel materials emulate
92
92
the basic electrochemical properties of their widely used solid counterparts while spanning a
wide range of oxidation potentials. Perhaps more importantly, we have shown that this synthetic
strategy is quite general, which may also extend to other popular classes of organic
semiconductors and possibly be used to produce other liquid organic semiconductor types in the
future. This work will hopefully help further the study of organic electronic devices
incorporating liquid layers and allow for the synthesis of device specific liquid materials.
93
93
6.3.5 References
1. a) Piers, W.E. The chemistry of perfluoroaryl boranes. In Advances in Organometallic
Chemistry; West, R., Hill, A.F., Eds.; Elsevier Academic Press: San Diego, 2005; Vol. 52,
1. b) Brook, M.A.; Grande, J.B.; Ganachaud, F. Adv. Polym. Sci. 2010, 235, 161-183.
2. Parks, D.J.; Piers, W.E. J. Am. Chem. Soc. 1996, 118, 9440-9441.
3. Rubinsztajn, S.; Cella, J. A. Macromolecules 2005, 38 (4), 1061-1063
4. Blackwell, J.M.; Foster, K.L.; Beck, V.H.; Piers, W.E. J. Org. Chem. 1999, 64, 4887-
4892.
5. Zhou, D.; Kawakami, Y. Macromolecules 2005, 16, 6902-6908.
6. Brook, M.A. Silicon in Organic, Organometallic, and Polymer Chemistry, John Wiley
and Sons, New York, 2000.
7. Thompson, D. B.; Brook, M. A. J. Am. Chem. Soc. 2008, 1, 32-33.
8. a) Chojnowski, J.; Fortuniak, W.; Kurjata, J.; Rubinsztajn, S.; Cella, J. A.
Macromolecules 2006, 11, 3802-3807. b) Chojnowski, J.; Rubinsztajn, S.; Fortuniak, W.;
Kujata, J. Inorg. Organomet. Polym. Mater. 2007, 17, 173-187 c) Cella, J.; Rubinsztajn,
S. Macromolecules 2008, 41, 6965-6971.
9. Grande, J.B.; Gonzaga, F.; Brook, M.A. Dalton Trans. 2010, 39, 9369-9378.
10. Grande, J. B.; Thompson, D. B.; Gonzaga, F.; Brook, M. A. Chem. Comm. 2010, 27,
4988-4990.
11. a) Parks, D.J.; Blackwell, J.M.; Piers, W.E. J. Org. Chem. 2000, 65, 3090-3098. b)
Blackwell, J.M.; Sonmor, E.R.; Scoccitti, T.; Piers, W.E. Org. Lett. 2000, 2, 3921-3923.
12. Thelakkat, M. Macromol. Mater. Eng. 2002, 287, 442-461.
13. (a) Hartwig, J. F.; Kawatsura, M.; Hauck, S. I.; Shaughnessy, K. H.; Alcazar Roman, L.
M. J. Org. Chem. 1999, 64, 5575. (b) Jiang, L.; Stephan, B. L. Palladium-Catalyzed
Aromatic Carbon-Nitrogen Bond Formation. Metal-Catalyzed Cross-Coupling Reactions,
2nd ed.; de Meijere, A., Diederich, F., Eds.; Wiley-VCH: 2004; Chapter 13. (c) Bender, T.
P.; Coggan, J. A.; McGuire, G.; Murphy, L. D.; Toth, A. E. J. US Patent 7,408,085, 2008.
(d) Bender, T. P.; Coggan, J. A. US Patent 7,402,700, 2008. (e) Bender, T. P.; Goodbrand,
94
94
H. B.; Hu, N. X.; US Patent 7,402,699, 2008. (f) Bender, T. P.; Coggan, J. A.; US Patent
7,345,203, 2008. (g) Coggan, J. A.; Bender, T. P. US Patent 7,332,630, 2008.
14. (a) Janiak, C.; Braun, L.; Scharmann, T.G.; Girgsdies, F. Acta. Crystallogr. Sect. C 1998,
C54 (11), 1722-1724. (b) Di Saverio, A.; Focante, F.; Isabella, C.; Resconi, L.;
Beringhelli, T.; D’Alfonso, G.; Donghi, D.; Maggioni, D.; Mercandelli, P.; Sironi, A.
Inorg. Chem. 2005, 44 (14), 5030-5041.
15. Szeghalmi, A.V.; Erdmann, M.; Engel, V.; Schmitt, M.; Amthor, S.; Kriegisch, V.; Nöll,
G.; Stahl, R.; Lambert, C.; Leusser, D.; Stalke, D.; Zabel, M.; Popp, J. J. Am. Chem. Soc.
2004, 126, 7834-7845.
16. Noviandri, I; Brown, K.N.; Fleming, D.S.; Fulvas, P.T.; Lay, P.A.; Masters, A.F.; Phillips,
L. J. Phys. Chem. B 1999, 103, 6713.
17. Saragi, T.P.I.; Spehr, T.; Siebert, A.; Fuhrmann-Lieker, T.; Salbeck, J. Chem. Rev. 2007,
107 (4), 1011-1065.
18. Wu, R.; Schumm, J.S.; Pearson, D.L.; Tour, J.M. J. Org. Chem. 1996, 61 (20), 6906-6921.
19. Brunner, K.; Dujken, A.; Börner, H.; Bastiaansen, J.J.A.M.; Kiggen, N.M.M.; Langeveld,
B.M.W. J. Am. Chem. Soc. 2004, 126 (19), 6035-6042.
20. Piers, W.E. The Chemistry of Perfluoroaryl Boranes. In Advances in Organometallic
Chemistry; West, R.; Hill, A.F. Eds.; Elsevier Inc. USA, 2005; Vol. 52, 1-76.
21. Kwaan, R.J.; Harlan, C.J.; Norton, J.R. Organometallics 2001, 20, 3818-3820.
22. Lambert, C.; Nöll, G. J. Am. Chem. Soc. 1999, 121, 8434-8442.
23. a) Nelsen, S.F.; Trieber, D.A.; Ismagilov, R.F.; Teki, Y. J. Am. Chem. Soc. 2001, 123,
5684-5694. b) Nelsen, S.F.; Tran, H.Q. J. Phys. Chem. A 1999, 103, 8139-8144.
24. Di Saverio, A.; Focante, F.; Camurati, I.; Resconi, L.; Beringhelli, T.; D`Alfonso, G.;
Donghu, D.; Maggioni, D.; Mercandelli, P.; Sironi, A. Inorg. Chem. 2005, 44 (14), 5030-
5041.
25. It is worth noting that attempts to generate 1•+ and 4d•+ quantitatively by the use of strong
oxidizing agents (SbCl5 or N(C6H4Br)3SbCl6) in toluene at ambient conditions resulted in
that the rapid formation of a precipitate.. Such species generally need to be formed in
coordinating/polar solvents to remain soluble. See Connelly, N.G.; Geiger, W.E. Chem.
Rev.1996, 96, 877-910
26. Bender, T.P.; Graham, J.F.; Duff, J.M. Chem. Mater. 2001, 13, 4105.
95
95
Chapter 7: Hole Mobility of a Liquid Organic Semiconductor
7.1 Executive Summary
This chapter was published as a letter in the Journal of Physical Chemistry Letters.
Brett A. Kamino, Timothy P. Bender, Richard A. Klenkler (2012), Journal of Physical
Chemistry Letters, 3 (8), 1002-1006. Figure and Schemes are reprinted with permission. Copyright 2011 American Chemical Society Over the course of the previous chapters (4-6), we demonstrated several methods to produce
liquid organic semiconductors from traditional semiconductors while retaining their useful
electrochemical properties. However, in order to evaluate their potential use in electronic
devices, more characterization was necessary. One of the most critical parameters in organic
semiconductors is the ability of the material to move either positive or negative charge. This
parameter is known as the charge carrier mobility and its value has many implications for
organic electronic devices. For liquid organic semiconductors, this value had only been measured
once in the literature and the measurements were not performed in depth. This left many
questions about the mechanism of transport and whether or not this complied with current
theories.
While working on this paper, I worked at the Xerox Research Centre of Canada to develop a
technique to measure the charge carrier mobility of our one of our materials and to investigate
how charge transport through the liquid state behaved when put in current theoretical models.
This project was very successful and I managed to develop a simple and practical method to
measure the charge carrier mobility of our liquids by modifying an existing setup developed by
Xerox. I was able to show that our materials do indeed move charge throughout the liquid state
and that the material behaved very similarly to conventional materials. As well, this behavior fit
very nicely into existing charge transport theories.
From this study, we can surmise that our liquid organic semiconductor materials retain their
useful charge transporting properties despite the large change in physical properties. This bodes
well for the eventual use of liquid organic semiconductors in organic electronic devices.
96
96
7.2 Statement of Contributions
The authorship of this paper is as follow: Brett A. Kamino, Timothy P. Bender, Richard
Klenkler. All experiments in their entirety were performed by me as all as all data analysis and
data interpretation. Richard Klenkler is a researcher at the Xerox Research Centre of Canada
familiar with the analytical technique used. The paper was written by me with input from both
T.P. Bender and R. Klenkler.
7.3 Paper
7.3.1 Abstract
The first detailed study of charge transport through a liquid organic semiconductor (LOS) is
reported with the goal of elucidating the effects of molecular motion on charge transport through
molecular liquids. Using a liquid, silyl ether-substituted triarylamine, hole transport mobilities
were obtained over a wide range of temperatures above the glass transition temperature of the
material. Analysis of this data reveals that molecular motion(s) have a negligible effect on
macroscopic charge transport through a molecular liquid. The results strongly resemble transport
behavior found in conventional, disordered solids and suggest that silyl ether-substituted LOSs
may be good candidates for integration into electronic devices, by those who are familiar with
the application of traditional triarylamines, where their unique physical state can or could be
exploited.
7.3.2 Body
Liquid organic semiconductors (LOSs) are an emerging class of materials for organic electronic
devices. While conventional organic semiconducting materials are designed to form highly
crystalline solids or morphologically stable glasses,1 LOSs are specifically intended to be free-
flowing liquids at room temperature. Such materials present several unique processing
advantages over their more typical counterparts, including solvent-free device processing and the
presumed ability to easily achieve intimate contact with nanostructured or mesoporous surfaces.
The utility of LOSs has been demonstrated in dye-sensitized solar cells,2 photorefractive
devices,3 as host materials in liquid active layer light emitting diodes,4,5 and several other device
types.6,7 However, this class of materials remains understudied. Until recently, only two LOSs
were known in the literature: tris(4-methoxyethoxyphenyl)amine (TMEPA)2 and N-(2-
97
97
ethylhexyl)carbazole.3−5 Our group has worked to expand the available set of LOSs by
developing several general synthetic methods that, by incorporation of siloxane or silyl ether
molecular fragments into conventional arylamine molecular structures (triarylamines and
carbazoles), yield LOSs.8−10 We have shown that these silicon−arylamine hybrid materials retain
their characteristic electrochemical properties while having vastly different physical properties
from their parent materials, including presenting themselves as liquids and waxes. Despite the
success of this strategy in producing a number of new LOSs, it remained unclear what effect the
substitution of the siloxane or silyl ether groups would have on the hole-transporting properties
of these materials, as charge transport through the liquid phase is poorly understood for organic
semiconductors. We are aware of only a single example of a charge transport measurement
through an LOS.11 In that report, Ribierre et al. show that the liquid semiconductor, N-(2-
ethylhexyl)carbazole, acts as a p-type semiconductor and has an order of magnitude higher hole
mobility than its equivalent polymeric, solid-state analogue (poly(N-vinylcarbazole)).
Additionally, the transport characteristics of several solid molecular semiconductors have been
studied above their glass transition, but this type of study is limited by the possibility of
crystallization of the material above the glass transition temperature (Tg) and the relatively high
temperatures required to achieve a liquid state. In this work, we study the hole-transporting
ability of a silyl ether-substituted triarylamine LOS: N,N-bis(4-(triisopropylsilyloxy)phenyl)-3,4-
dimethylaniline (2TIPS, Figure 7-1a), a material that is a liquid at room temperature (Tg = −28
°C). Time-of-flight photocurrent measurements12 were performed on samples of 2TIPS doped
into a solid polymeric matrix and of 2TIPS as a neat liquid. The goals were to validate the
charge transporting capability of a silyl ether-substituted triarylamine and to begin to understand
whether charge transport in the liquid phase adheres to conventional theories explaining charge
transport through amorphous molecular solids. In particular, we were interested to see whether
the charge transport characteristics of an LOS can be described by the disorder formalism model
using 2TIPS as a model system. Developed by Bässler and co-workers,13 this model has been
used to successfully describe the transport behavior seen in many conventional organic
semiconducting materials, including those based on triarylamines. 2TIPS (Figure 7-1a) was
chosen as a model compound, because we have previously shown that it has predictable
electrochemical behavior8 and is a member of the well-studied triarylamine family of hole
transport compounds.14
98
98
a)
5.00E-04 5.00E-03 5.00E-02
Vo
lta
ge
(a
.u.)
Time (s)
ttransit
CG
L
Al
Al
2T
IPS
/Po
ly(s
tyre
ne
)
Laser Pulse
+-
5 x 10-3 5 x 10-25 x 10-4
(b)
2.00E-03 2.00E-02 2.00E-01
Vo
lta
ge
(a
.u.)
Time (s)
ttransit
CG
L
Al
Ka
pto
n
Sp
ace
r
Ka
pto
n
Sp
ace
r
Al
2T
IPSLaser Pulse
+-
TP
D
2 x 10-22 x 10-3 2 x 10-1
Figure 7-1: Example photogenerated transients through (a) 2TIPS in a poly(styrene) matrix (9 um) and (b) neat 2TIPS (50 um) with the calculated transit time shown (Note: y-axis is linearly scaled while x-axis is logarithmic). Device structures are illustrated next to their respective transients and the chemical structure of 2TIPS is shown.
99
99
We began our study by investigating the basic transport properties of 2TIPS doped into an inert
polymer matrix. Polymers commonly used include polystyrene and polycarbonate-A.
Polystyrene was chosen as the inert matrix as it formed higher quality films when doped with
2TIPS than did polycarbonate-A. The time-of-flight cell (Figure 7-1a, inset) was assembled in a
similar manner to what we have previously described.15 Specifically, a Mylar substrate metalized
with an aluminum electrode was sequentially coated with a silane blocking layer, a charge
generator layer (CGL, composed of a hydroxygallium phthalocyanine dispersion in a polymer
binder) and a blade coated hole-transport layer consisting of 2TIPS and polystyrene at a 1:1 ratio
(by weight). The cell was completed by pressure contact with a second metalized Mylar
electrode. The time-of-flight measurements were performed as described by Melnyk and Pai,12
using a nitrogen pulse laser with a dye attachment (Laser Science VSL-337ND-S & DUO-220).
The output laser wavelength was tuned to 650 nm, so as to be only absorbed by the CGL, and
laser intensity was adjusted such that less than 1/10 CV (where, C is the device capacitance and
V the applied bias) of charge was injected; this ensured that charge transport would not be space
charge limited.12 Signal transients were collected at different field strengths, transport layer
thicknesses, and temperatures. These measurements showed characteristics typical of
triarylamines blended with an inert polymer (Figure 7-1a).16 In order to validate our technique,
transients were measured as a function of transport layer thickness over a range of 5−37 µm.
Transit times (and hence mobility) were found to scale linearly with thickness (Figure S7-1,
section 12.5), confirming that the transient signals are indeed due to transport across the entire
thickness of the transport layer and that the calculated mobilities were not an artifact of the
system. Field-dependent mobility over a temperature range of −30 to 65 °C was measured and is
shown in Figure 7-2a for a 9 µm thick hole-transport layer. The transients were non-dispersive as
indicated by a plateau of current followed by a well-defined drop in current defining the transit
time. Hole-transport mobilities were found to be weakly field dependent across the temperature
range (Figure 7-1a). Comparing measurements at variable temperatures, we find that the mobility
is strongly temperature activated until we reach the glass transition temperature of the polymer
blend (measured to be 48 °C)17 where this dependence plateaus. This behavior at the glass
transition temperature has been previously observed in doped polymers,18 molecular glasses,19
and polymeric semiconductors.20 In order to see whether 2TIPS behaved similarly to other
triarylamines, the results were analyzed within the context of the disorder formalism:
100
100
Σ−
−= 2/12
22
0 exp3
2exp),( E
kTC
kTET
σσµµ 7-1
where µ is the mobility, µ0 is the mobility at infinite temperature and zero field, σ is the width of
the density-of-states in eV, k is the Boltzmann constant, T is the absolute temperature, Σ
describes the positional disorder, C is an empirical constant, and E is the applied electric field.
This equation describes the dependence of charge carrier mobility on temperature and electric
field and predicts that log µ should scale linearly with the inverse square of temperature and the
square of the electric field. Excluding the points at and above the glass transition temperature,
the data collected for the 2TIPS/polystyrene films shows the expected dependence (Figure 7-2a).
By extrapolating the mobilities to an electric field of zero, the values of µ0 and σ were found to
be 1.92 × 10−3 cm2 V−1 S−1 and 0.104 eV, respectively. When compared to other triarylamines
found in the literature, these values are in line with other well-known, non-liquid triarylamines,
including TPD and TAPC.21,22
a)
1.00E-07
1.00E-06
1.00E-05
300 500 700
Ho
le M
ob
ilit
y (
cm
-2v
-1s
-1)
E1/2 (V/cm)1/2
+ 65 °C
- 30 °C
+ 20 °C
1 x 10-6
1 x 10-5
1 x 10-7
101
101
(b)
1.00E-07
1.00E-06
1.00E-05
1.00E-04
150 250 350
Ho
le M
ob
ilit
y (
cm
2V
-1s
-1)
E1/2 (V/cm)1/2
1 x 10-5
1 x 10-7
1 x 10-4
- 40 °C
+ 60 °C
+ 20 °C
1 x 10-6
Figure 7-2: Field dependent hole mobility as a function of temperature for 2TIPS in a (a) polystyrene matrix and (b) as a neat liquid.
For the time-of-flight measurement of 2TIPS as a neat liquid, a different cell design was
required. Empty cells were assembled by sandwiching two strips of Kapton (polyimide) film
between the same two Mylar substrates described above and gently clipping them together
(Figure 7-1b, inset). Once prepared, the empty cell was heated to 50 °C, and the neat 2TIPS was
drawn into the cell by capillary action. Unfortunately, this setup produced weak photocurrents
and highly dispersive transients, making accurate determination of the mobilities impossible. It
was found that adding a thin (275 nm) layer of TPD on top of the hydroxy gallium
phthalocyanine layer by physical vapor deposition increased photocurrent and improved the
resolution of the transient so that a sharp and distinct transit time could be observed and defined.
The cell design and an example transient are illustrated in Figure 7-1b. The additional TPD layer
seems to improve charge injection between the phthalocyanine layer and 2TIPS, but the rising
plateau in the transient is indicative of the slow release of a well of charge in the CGL. This
manifests itself in a measured current that steadily increases over time until the transit time
(Ttransit, Figure 7-1b) is reached, possibility indicating a charge injection barrier. If a charge
injection barrier exists on a time scale similar to the transit time, the results of this experiment
would certainly be invalidated.23 To investigate this possibility and validate the fidelity of the
102
102
technique, transients were measured as a function of transport layer thickness over a range of
50−125 um (as defined by the thickness of the Kapton spacer). Again, transit times and mobility
were found to scale linearly with thickness of the 2TIPS layer (Figure S7-2, section 12.5),
thereby confirming that the mobility values being measured are independent of any charge
injection issues.
As a point of comparison, we measured the mobility of N-(2-ethylhexyl)carbazole, an LOS with
a known hole transport mobility.11 The compound was synthesized by the method outlined in the
9.5.1, and a time-of-flight cell with this material was prepared in the same manner as described
above (Figure 7-1b), including the additional 275 nm TPD interlayer. Transients were obtained
over a variety of fields, and the field-dependent mobilities agreed well with those previously
reported for this material, albeit at a lower field strength (Figures S7-3 and S7-4, section 12.5).
This confirmation of the known hole-transport mobility of N-(2-ethylhexyl)carbazole provides
further validation of our experimental setup.
Using a 2TIPS cell with a 50 um Kapton spacer and the TPD interlayer, field-dependent
transients were collected between −40 and 60 °C (Figure 7-2b). However, it was only possible to
collect transients through a narrow range of field strengths. For most samples, increasing the
field strength over 1 × 105 V/cm resulted in shorting the device. At very low temperatures, this
effect was not observed, and higher field strengths were found to be necessary to achieve
measurable signals. Much like the 2TIPS/polystyrene samples, results for the neat 2TIPS cells
were interpreted within the context of the disorder formalism (eq. 7-1). From Figure 7-2b, we
can see that log µ scales with E1/2 showing a weak dependence on field strength like that which
was observed for the solid sample. Plotting the temperature dependent mobility at different field
strengths again shows a linear relationship between log µ versus T−2 similar to the data observed
for the solid 2TIPS/polystyrene system (Figure 7-3). Interestingly, the majority of the data points
obtained on this line correspond to values above the Tg of 2TIPS (Tg = −28 °C).9 This
relationship implies that charge transport through liquid 2TIPS is governed by temperature-
activated hopping, as predicted by the disorder formalism and as is seen in most disordered
solids. This relationship holds true for the entire range of values above the Tg of this compound,
a span of approximately 90 °C. This represents the first investigation into the effect of
temperature on charge mobility in an organic molecular liquid and invites discussion into the role
103
103
of molecular motion on the charge transport process. Analysis of the extrapolated zero field
mobilities gives µ0 and σ values of 8.89 × 10−2 cm2 V−1 s−1 and 0.115 eV, respectively.
Comparing these parameters to those determined for the solid 2TIPS/ polystyrene system, we
find that the prefactor mobility (µ0) scales with the increased hole-transport mobilities observed
in this sample while the width of the density-of-states (σ) is somewhat larger than what was
determined for the solid sample. This is contrary to the expected trend found in typical materials.
In most solid-state examples, it is expected that the density of states decreases in energy when
going from a dilute sample (2TIPS doped into polystyrene) to a more concentrated sample (neat
2TIPS).24 In this case, the observed increase in the density of states can be explained by the
increased local motions of individual hole transport molecules when going from a solid to a
liquid.25
1.00E-07
1.00E-06
1.00E-05
1.00E-04
1.00E-03
6 11 16(1000/T)2 (K-2)
Neat 2TIPS
2TIPS/poly(styrene)
Tg1 x 10-6
1 x 10-7
1 x 10-5
1 x 10-4
1 x 10-3
Mo
bilit
y (
cm
2V
-1s
-1)
Figure 7-3: Temperature dependence on hole mobility for 2TIPS doped in polystyrene (50 wt%) at 555 kV/cm and neat 2TIPS at 100 kV/cm. The glass transition temperature of the polymer blend is indicated as Tg at 48 °C.
Temperature-driven changes in the density-of-states due to molecular motion and solvation
energy have been proposed to describe deviations in temperature-dependent mobility behavior
above the glass transition temperature in solid systems.26 However, this is still a poorly
understood phenomenon that produces very different behaviors for various material types. For
most doped polymer systems (as observed for 2TIPS/polystyrene in this letter), the glass
104
104
transition is characterized by the onset of temperature-independent mobility. Other systems have
shown an inversion in the mobility dependence20 or even a continuation of normal behavior well
above the glass transition temperature.19 Our LOS was studied well above its glass transition and
displays quite pedestrian behavior throughout this range. In fact, the only difference found was a
slight increase in the density of states compared to the solid polymeric sample. If molecular
motions were important to charge transport through a LOS, we would expect a deviation from
normal temperature-dependent behavior due to an increase in physical diffusion at higher
temperatures. The absence of such an effect strongly suggests that molecular motions have a
negligible effect on the hole-transport mobility of our system.
In summary, the charge transporting properties of a silyl ether-substituted liquid triarylamine,
2TIPS, was studied. As both a dopant in an inert polymer matrix and as a neat liquid, the charge
transport molecule exhibited conventional hole transporting properties when studied using a
time-of-flight technique. Most interestingly, the charge mobility of neat 2TIPS closely followed
the temperature dependence predicted by the disorder formalism model for solid materials. This
behavior is observed over a large range of temperatures above the Tg, and we conclude that
molecular motion has a negligible effect on macroscopic charge transport in this material save
for a small increase in the density of states. The conventional charge mobility behavior of these
materials suggests that silyl ether-functionalized LOSs may be excellent targets for integration
into novel, liquid electronic devices by those who are familiar with traditional solid triarylamines
but who might want to exploit the novel liquid state of LOSs.
7.3.3 References
1. Shirota, Y.; Kageyama, H. Chem. Rev. 2007, 107, 953,-1010.
2. Snaith, H.J.; Zakeeruddin, S.M.; Wang, Q.; Péechy, P.; Grätzel, M. Nano. Lett. 2006, 6, 2000.
3. Ribierre, J.; Aoyama, T.; Kobayashi, T.; Sassa, T.; Muto, T.; Wada, T. J. Appl. Phys. 2007, 102, 033106.
4. Hirata, S.; Kubota,, K.; Jung, H.H.; Hirata, O.; Goushi, K.; Yahiro, M.; Adachi, C. Adv.
Mater. 2011, 23 (7), 889-893.
5. Xu, D.; Adachi, C. Appl. Phys. Lett. 2009, 95, 053304.
6. Hendricks, E.; Guenther, B. D.; Zhang, Y.; Wang, J. F.; Staub, K.; Zhang, Q.; Marder, S. R.; Kippelen, B.L.; Peyghambarian, N. Chem. Phys. 1999, 245, 407.
105
105
7. Ribierre, J.C.; Aoyama, T.; Muto, T.; André, P. Org. Electron. 2011, 12 (11), 1800-1805.
8. Kamino, B.K.; Grande, J.B.; Brook, M.A.; Bender, T.P. Org. Lett. 2011, 13, 154-157
9. Kamino, B.K.; Castrucci, J.; Bender, T.P. Silicon, 2011, 3 (3), 125-137.
10. Kamino, B.K.; Mills, B.M.; Reali, C.; Bender, T.P. J. Org. Chem. 2011, 77 (4), 1663-
1674.
11. Ribierre, J.-C.; Aoyama, T.; Muto, T.; Imase, Y.; Wada, T. Org. Electron. 2008, 9, 396-400.
12. Melnyk, A.R.; Pai, D.M. Physical Methods of Chemistry, 2nd ed., Vol. VIII, Rossiter, B.W.; Baetzold, R.C., Eds.; Wiley, New York, 1993; Chapter 5, 321-386.
13. Auweraer, M.V.; Schryver, F.C.D.; Borsenberger, P.M.; Bässler, H. Adv. Mater. 1994, 6 (3), 199-213.
14. Borsenberger, P.M.; Weiss, D.S. Organic Photoreceptors for Xerography; Marcel Dekker, Inc.: New York, 1998.
15. Klenkler, R.A.; Xu, G.; Graham, J.F.; Popovic, Z.D. App. Phys. Lett. 2006, 88, 102101
16. Borsenberger, P.M. J. Appl. Phys. 1990, 68, 6263-6273.
17. Glass transition of polymer blend determined through differential scanning calorimetry.
18. Abkowitz, M.; Stolka, M.; Morgan, M. J. Appl. Phys. 1981, 52(5), 3453-3457.
19. Bässler, H.; Borsenberger, P.M. Chem. Phys. 1993, 177, 763-771.
20. Abkowitz, M.A.; McGrane, K.M.; Knier, F.E.; Stolka, M. Mol. Cryst. Liq. Cryst. 1990, 183, 157-169.
21. Borsenberger, P.M.; Gruenbaum, W.T.; Magin, E.H.; Sorriero, L.J. Chem. Phys. 1995, 195, 435-442.
22. N,N`-diphenyl-N,N`-bis(3-methylphenyl)-(1,1`-biphenyl)-4,4`-diamine (TPD) and 1,1-bis(di-4-tolylaminophenyl)cyclohexane (TAPC).
23. Chen, I. Jpn. J. App. Phys. 1989, 28, 21.
24. Schein, L.B.; Borsenberger, P.M. Chem. Phys. 1993, 177, 773-781.
25. Borsenberger, P.M.; Pautmeier, L.; Bässler, H. J. Chem. Phys. 1991, 95 (2), 1258-1265.
26. Bässler, H. Adv. Mater. 1993, 5 (9), 662-665.
106
106
Chapter 8: Crosslinked Triarylamine-Siloxane Films using Piers-Rubinsztajn Chemistry
8.1 Executive Summary
This chapter is a draft of paper that will be submitted as a communication to Macromolecular
Rapid Communications.
The author list will be as follows:
Brett A. Kamino, Anjuli Szawiola, Ishan Gupta, Michael J. Gretton, Timothy P. Bender.
This work represents a conceptual extension to the work done in the previous chapters on
creating siloxane-triarylamine hybrid materials. In this work, we try to exploit the previously
developed chemistry and methods to create cross-linked organic semiconductor films instead of
liquid organic semiconductors. Such cross-linked films have the potential to be more easily
incorporated into organic semiconducting devices than liquid organic semiconductors. Such
materials have already been demonstrated successfully in a number of devices. This chapter is
the final project on my main thesis project and demonstrates that our synthetic approach to
siloxane-triarylamine hybrid materials can be extended to other forms of matter relatively easily.
This chapter is a proof of concept of this particular approach and further optimization and
integration into devices will be one of the challenges left to future graduate students.
8.2 Statement of Contributions
The author list for this paper is as follows: Brett A. Kamino, Anjuli Szawiola, Ishan Gupta,
Michael J. Gretton, Timothy P. Bender. I came up with the primary concept for this project and
the designed of all materials and processes used. As well, I led the development of experiments,
performed most of the analytical technqiues myself, and solely analyzed and processed all data.
Anjuli Szawiola and Inshan Gupta assisted with synthesis of compounds and elaboration of
synthetic techniques developed by me. Additionally, Anjuli Szawiola performed a portion of the
IR and photoluminescence expeirments under my direction. Writing of this chapter was
performed by me with input from both Anjuli Szawiola and Michael J. Gretton.
107
107
8.3 Paper Draft
8.3.1 Abstract
A cross-linked thin film with a triarylamine monomer has been synthesized by Piers-Rubinsztajn
chemistry from readily available materials to be used as a charge-transport layer in organic
electronic devices. The triarylamine compound was synthesized and functionalized with a cyclic
ether that upon ring-opening, participates in cross-linking with tetrakis(dimethylsiloxy)silane
forming smooth, glassy films. Various catalyst loadings and curing temperatures were tested to
determine their effect on film quality. It was found that the films were electrochemically active
and amorphous, with low glass transition temperatures. In addition, while curing temperature
was found to have little effect on monomer aggregation, catalyst loading had a substantial
influence, presumably due to the higher cross-link density formed with a higher catalyst loading.
8.3.2 Introduction
Silane activation by tris(pentafluorophenyl)borane,1 or the Piers-Rubinsztajn reaction,2 is a
powerful method for the construction of silicon heteroatom bonds. Using this chemistry, a
number of organic reactions such as hydrosilylation of carbonyl groups,3 silyl ether formation
through dehydrocarbonative condensation,4 and metal-free reductions5 can be achieved using
mild reaction conditions with good functional group tolerance.6 Additionally, this chemistry
benefits from the use of easily handled and commercially available silanes as a silicon source.
Beyond simple organic transformations, the Piers-Rubinsztajn reaction has been used to produce
a number of functional materials and polymers. Among these, Rubinsztajn and coworkers have
shown how this chemistry can be used to rapidly build well-defined siloxane-organic copolymers
from simple starting materials.7,8 Other examples of this reaction’s use with silicones include the
synthesis of explicit siloxane dendrimers9 and silicone surfactants.10 More recently, our group
has found that the Piers-Rubinsztajn reaction is a convenient method for the functionalization of
charge transporting materials with silicone or siloxane groups. Using this strategy, we have been
able to prepare a range of different siloxane/charge transporting hybrid materials with extremely
varied physical properties ranging from polymeric glasses11 to low Tg molecular liquids.12,13
Despite the large change in physical properties that results from this transformation, we have
shown that the useful electronic properties of the charge transporting materials remain
unchanged.14
108
108
Given the proven utility of Piers-Rubinsztajn chemistry for producing functional organic
semiconducting materials, one may consider the possibility of using this chemistry to produce
cross-linked films incorporating organic charge transporting molecules. Cross-linked films
containing charge transporting layers have many applications in organic electronic devices and
many advantages over conventional small molecules and polymers. These advantages include
improved morphological stability,15 and the ability to solution deposit additional layers on top of
the cross-linked layer.16 Such chemically cross-linked layers have been successfully
demonstrated in organic photovoltaics,17 organic light emitting diodes,18 and organic field effect
transistors.19 Interestingly, several silicone based cross-linking systems have been previously
reported and shown to be immensely useful as charge transporting layers in organic electronic
devices.20-22 In these previously reported silicone systems, charge transporting compounds were
functionalized with trichloro or trialkoxy silanes and polymerized by sol-gel chemistry.23 Thin
films made with these systems have been successfully used in OLEDs as hole transporting
compounds as well as emitting layers.
While crosslinking formulations based on silicone polycondensation methods have shown to be
very effective as layers in electronic devices, there are some synthetic disadvantages inherent to
this chemistry. First, this chemistry requires the introduction of water and an acid into the
formulation. Water has been shown to be one of the chief factors in device degradation and even
miniscule amounts can limit the life span of organic electronic devices.24,25 The second major
disadvantage is the need to functionalize the charge-transporting molecule with a reactive silane
group. This additional functionalization step increases the total number of synthetic steps
required and adds difficulty to the purification and isolation of the final monomer.
In this communication, we demonstrate how Piers-Rubinsztajn chemistry can be used to produce
high quality cross-linked films from very stable and easily synthesized reagents under non-
hydrolytic conditions. The key to this achievement is the use of cyclic ethers as substrates rather
than hydroxyl alkoxy groups. Film formulation is explored by studying the thermal,
photophysical, and electrochemical properties of these films.
109
109
8.3.3 Results and Discussion
Before we began the development of a cross-linking system based on Piers-Rubisnztajn
chemistry, we had to deal with aspects of this chemistry that were not favourable towards thin-
film formation. Specifically, our previous conditions11-13 for the addition of siloxane fragments
to triarylamine structures involved reacting aryl methoxy groups with silanes using
tris(pentafluorophenyl)borane (BCF) to promote the reaction. Under these conditions, the
reaction results in the rapid release of stoichiometric amounts of hydrocarbons and a noticeable
amount of heat. This uncontrollable reaction speed at room temperature and rapid release of
gases poses certain problems when trying to reproducibly obtain smooth cross-linked films. The
vigorous nature of this chemistry has in fact been recently shown to produce elastomeric foams
under certain conditions.26
In order to develop a cross-linking system based on Piers-Rubinsztajn chemistry incorporating
charge transporting triarylamines, we needed a formulation which reacts more controllably and
does not release any volatile gases. To achieve this, we chose to synthesize a triarylamine27
based monomer incorporating two 2,3-dihydrobenzofuran groups to react in our cross-linking
system. Using dihydrofuran groups instead hydroxyl or alkoxy groups to react with a silane
offers several key advantages. Firstly, when reacted with a silane under Piers-Rubinsztajn
conditions, cyclic ethers ring-open instead of displacing a volatile hydrocarbon.5 This eliminates
the problem of bubble formation inside the film. The second advantage is a slower rate of
reaction due to non-productive binding of the catalyst to the Lewis-basic dihydrofuran and
decreased nucleophilicity of the cyclic ether as compared to an alkoxy or hydroxyl group.†
110
110
N N
O
Si
O
Si O
Si
O
Si
O O
Br
8-1
(i)
(iii)
8-4
(ii)
N
N
O
O
8-3
(iv)
NH2
O
HN
8-2
8-2
Scheme 8-1: Synthesis of an arylamine monomer for ring-opening under Piers-Rubinsztajn
conditions. (i) NBS, THF, rt, 16hrs, 89% (ii) Pd(OAc)2, P(t-butyl)3, NaO(t-butyl), toluene, 110°C
70%. (iii) Pd(OAc)2, P(t-butyl)3, NaO(t-butyl), toluene, 110°C, 85%. (iv) 1,1,1,3,3-
pentamethyldisiloxane, tris(pentafluorophenyl)borane, toluene, rt, 78%.
2,3-Dihydrobenzofuran was incorporated into the structure of the arylamine by first brominating
it using NBS and then using successive Buchwald-Hartwig28 coupling steps to form the
arylamine monomer (8-3) (Scheme 8-1). Before attempting any cross-linking and film formation
with this monomer, we reacted it with a mono-functional silane (1,1,1,3,3-
pentamethyldisiloxane) under standard Piers-Rubinsztajn conditions to test its reactivity. Under
these conditions, the desired ring-opening reaction proceeded smoothly over the course of
several minutes releasing a noticeable exotherm and no gaseous byproducts to yield compound
8-4 as confirmed by 1H, 29Si, and 13C NMR and HRMS. This small molecular analogue was
isolated as a pale yellow glass which crystallized on sitting over several months.
With confirmation of the desired reactivity in our monomer, we set about synthesizing cross-
linked films with a number of poly-functional silanes. Our initial attempts to use commercial
111
111
poly(methylhydrosiloxane-co-dimethylsiloxane) and poly(methylhydrosiloxane-co-
phenylmethylsiloxane) as comonomers failed to produce homogeneous films under a number of
conditions. These films displayed significant phase separation, poor surface quality, and
somewhat temperamental curing conditions often resulting in unreacted polymer remaining. We
had greater success using tetrakis(dimethylsiloxy)silane (QM4) which consistently resulted in
high quality films upon drying of the solvent (Scheme 8-2). We suspect that this success is due
to better phase compatibility of the two components and more favourable kinetics resulting from
a less sterically hindered silane group. Using these components, smooth glassy films were
produced by drop casting the formulations on glass substrates. The resulting films remained
optically clear over 2 months of storage in ambient conditions and did not appreciably swell
when soaked in common non-polar solvents such as toluene and chloroform.
Scheme 8-2: Reagents used to achieve functional cross-linked films using Piers-Rubinsztajn
chemistry. (v) tris(pentafluorophenyl)borane, toluene.
112
112
Table 8-1: Collected experimental information for different formulation conditions.
To explore the scope and versatility of this crosslinking system, six formulation conditions were
studied which varied in curing temperature and catalyst loading (Table 8-1). Under all
conditions, smooth, homogenous, and glassy films were obtained by drop casting the solutions
onto glass slides and curing the films for 30 minutes in air.‡ To understand the extent of the
reaction, IR spectroscopy was performed on the films and compared to QM4 to determine if
residual Si-H groups remained in the film. The films using 1-2 mol% catalyst relative to QM4
(Films A-E) all looked very similar by IR and did not show any residual Si-H stretching peak
(see section 12.6). The film with the lowest catalyst loading (Film F) however, did show a small
amount of residual Si-H peak in the IR (Figure 8-1). From these spectra we can conclude that
under most of our film formation conditions, virtually quantitative consumption of Si-H groups
is observed. At first, this observation is somewhat curious given the small excess of Si-H groups
in each formulation (~4 mol%). However, since the cross-linking reaction is performed in air, it
is likely that adventitious water in the atmosphere is able to react with Si-H to condense two
QM4 groups together.1 From this IR study we can conclude that 1 mol% BCF catalyst is required
for full consumption of Si-H groups under these conditions.
113
113
65011501650215026503150
Tra
nsm
itta
nce
Wavenumber (cm-1)
0.5 mol%
1 mol%
2 mol%
QM4
Si-H
F
E
D
Figure 8-1: IR spectra of QM4 and films 6, 5, and 4 (top to bottom). Film D prepared in a matrix
of KBr and the remainder studied by ATR.
The films were then characterized by differential scanning calorimetry (DSC) and thermal
gravimetric analysis (TGA) to gain further insight into their morphology and structure. Using
DSC, we found that all of the films displayed a single glass transition just above room
temperature on both the heating and cooling cycles (Tg, Table 8-1) with no crystalline transitions
observed. TGA performed on the films revealed a bimodal decomposition pattern for all films.
In each case, five percent mass loss occurred at fairly low temperatures (~140 to 170 °C, Table
8-1) followed by a plateau at around 90-93% mass. Decomposition accelerated again above ~400
°C. As a point of comparison, TGA was also run on our model compound (8-4) which showed
only a single, sharp decrease in mass with 5 wt% loss at 326 °C. The significant mass loss in the
films at relatively low temperatures can be explained by the likely presence of small amounts of
oligomers and trapped solvent within the film itself. Minimizing this loss of material is an
important consideration in the eventual use of these films in organic electronic devices.
Interestingly, we can correlate the glass transition temperature of the films to the thermal
stability. Films with higher thermal stability also have higher glass transition temperatures. We
114
114
suspect that this correlation is reflective of the effective cross-link density in the films and that
films with the highest Tg or Td have the highest cross-link density. From these data, several
trends in the formulation parameters can be identified. Catalyst concentration has a positive
effect on cross-link density of the films which agrees well with the previously mentioned IR
results. Looking at the effect of temperature, we find that films cured at 50 °C have highest
cross-link density compared to films cured at higher or lower temperatures. This can be
explained by two competing temperature effects during film formation. Higher reaction
temperatures likely increase the overall curing rate, but higher temperatures also increase the rate
of solvent evaporation. Because of the need for catalyst mass transport in this system, solvent
inclusion is probably necessary for a high cross-linking density.
To help understand the conformation of the redox active triarylamine monomers within the
films, both the films themselves and the model compound (8-4) were studied by
photoluminescence (PL) spectroscopy. PL spectra of compound 8-4 was obtained in dilute THF
solutions and in the solid-state (Figure 8-2a). A significant red shift was observed between the
two samples with the solid state sample having a λmaxex of 449 nm versus 410 nm for the same
compound in solution. This red shift is indicative of intermolecular aggregation affects and can
serve as a good tool to probe the intermolecular interactions of the cross-linked films.29,30 All six
films were studied in the solid-state. Films A, B and C were found to have near identical spectra
with a λmaxex of ~432 nm (Figure 8-2b, Table 8-1) with a smaller shoulder at shorter wavelengths.
A peak shape comparison to the model compound reveals that some intermolecular aggregation
is occurring but curing temperature in this range has a small impact on this effect. Interestingly,
films at a higher temperature (D, E and F) were found to have a more red shift spectrum with F
having the greatest amount of red shifting. From the thermal characterization experiments, we
suspect that these films have lower cross-linking densities. This may allow for more aggregation
between specific components in the solid-state and result in a more red-shifted
photoluminescence spectrum. Spectra for the remaining films are illustrated in section 12.6.
115
115
0
0.2
0.4
0.6
0.8
1
0
0.2
0.4
0.6
0.8
1
285 335 385 435 485 535 585
No
rma
lize
d P
L I
nte
ns
ity
Ab
so
rba
nc
e (
a.u
).
Wavelength (nm)
0
0.2
0.4
0.6
0.8
1
385 435 485 535 585
No
rmali
zed
PL
In
ten
sit
y
Wavelength (nm)
A D F
Figure 8-2: (a) UV-Vis absorption (black) and photoluminescence spectra of compound 4 in a
THF solution (red) and a neat film (blue). (b) Photoluminescence spectra of films A, D, and F on
glass.
Finally, electrochemical characterization was performed on both the small molecule model
compound (4) and film D. Compound 8-4 was studied by solution cyclic voltammetry in DCM
(Figure 8-3) and displayed two reversible oxidations at 655 mV and 910 mV vs. Ag/AgCl. This
behaviour is fairly typical for bis-arylamines. Film D was studied as a thin film on ITO in both
acetonitrile and aqueous solutions. The films studied in acetonitrile yielded two poorly resolved
oxidation waves similar to compound 8-4 (Figure 3). This oxidation was found to be only
partially reversible as subsequent scans yielded smaller and smaller currents. Differential pulse
voltammetry on a fresh film was performed to help resolve each oxidation peak and yielded two
oxidations with peaks at 790 mV and 905 mV vs. Ag/AgCl. Films studied in aqueous solutions
only showed a single, fully irreversible oxidation peak (see section 12.6). Subsequent voltage
sweeps on these films yielded zero redox activity. Regardless of this instability, the behaviour of
these films on ITO confirms that the cross-linked films remain electrochemically active after
reaction. The differences in redox potentials between the films in acetonitrile and the model
compound (8-4) can be attributed to differences in working electrode material, solvent, and
differences in molecular conformation in the solid-state.
116
116
-0.4 -0.2 0 0.2 0.4 0.6 0.8 1 1.2
Cu
rre
nt
(a.u
.)
Voltage (vs. Ag/AgCl)
Reference
(a)
(b)
(c)
Figure 8-3: Electrochemistry with decamethylferrocene internal reference. (a) cyclic voltammetry of 8-4 in DCM. (b) cyclic voltammetry of film D on ITO in acetonitrile. (c) differential pulse voltammetry of film D on ITO in acetonitrile.
8.3.4 Conclusions
We have successfully demonstrated the first use of Piers-Rubinsztajn chemistry to achieve cross-
linked silicone films with a redox active component. The use of cyclic ethers proved to be
critical in formulating compositions that reproducibly and controllably reacted to give smooth
glassy films. Complete consumption of all Si-H groups was found to be achieved with low
catalyst loadings and the resulting films were found to be amorphous with low glass transition
temperatures. Photophysical characterization of the films showed that minimal aggregation of
the redox active triarylamine monomers could be achieved by altering the formulation
parameters. Electrochemical characterization of the films confirmed that they retained the
electrochemical activity of the monomer. Future work will include exploring how other film
properties can be further tuned using new monomers and integration of the current films in
organic electronic devices.
117
117
8.3.5 References
† This decrease in reactivity can be evidenced by the reaction of 3-hydroxytetrahydrofuran
where the hydroxy group is reacted in excellent yields over the hydrofuran group.4
‡ Films made at room temperature (entry 4) were cured for 2 hours.
1. Piers, W. E.; Marwitz, A. J. V.; Mercier, L. G. Inorg. Chem. 2011, 50, 12252.
2. Brook, M. A.; Grande, J. B.; Ganachaud, F. Adv. Polym. Sci. 2011, 235, 161.
3. Parks, D. J.; Piers, W. E. J. Am. Chem. Soc. 1996, 118, 9440.
4. Blackwell, J. M.; Foster, K. L.; Beck, V. H.; Piers, W. E. J. Org. Chem. 1999, 64, 4887.
5. Gevorgyan, V.; Liu, J.-X.; Rubin, M.; Benson, S.; Yamamoto, Y. Tett. Lett. 1999, 40, 8919.
6. Grande, J. B.; Thompson, D. B.; Gonzaga, F.; Brook, M. A. Chem. Comm. 2010, 27, 4988.
7. Rubinsztajn, S.; Cella, J. A. Macromolecules 2005, 38, 1061.
8. Cella, J.; Rubinsztajn, S. Macromolecules 2008, 41, 6965.
9. Thompson, D. B.; Brook, M. A. J. Am. Chem. Soc. 2007, 130, 32.
10. Grande, J. B.; Gonzaga, F.; Brook, M. A. Dalton Trans. 2010, 39, 9369.
11. Gretton, M. J.; Kamino, B. A.; Bender, T. P. Macromolecules 2011, 45, 723-728.
12. Kamino, B. A.; Grande, J. B.; Brook, M. A.; Bender, T. P. Org. Lett. 2010, 13, 154.
13. Kamino, B. A.; Mills, B.; Reali, C.; Gretton, M. J.; Brook, M. A.; Bender, T. P. J. Org.
Chem. 2012, 77, 1663.
14. Kamino, B. A.; Bender, T. P.; Klenkler, R. A. J. Phys. Chem. Lett. 2012, 3, 1002.
15. Helgesen, M.; Sondergaard, R.; Krebs, F. C. J. Mater. Chem. 2010, 20, 36.
118
118
16. Ma, B.; Lauterwasser, F.; Deng, L.; Zonte, C. S.; Kim, B. J.; Fréchet, J. M. J.; Borek, C.;
Thompson, M. E. Chem. Mater. 2007, 19, 4827.
17. Hsieh, C.-H.; Cheng, Y.-J.; Li, P.-J.; Chen, C.-H.; Dubosc, M.; Liang, R.-M.; Hsu, C.-S. J.
Am. Chem. Soc. 2010, 132, 4887.
18. Nuyken, O.; Bacher, E.; Braig, T.; Fáber, R.; Mielke, F.; Rojahn, M.; Wiederhirn, V.;
Meerholz, K.; Müller, D. Designed Monomers and Polymers 2002, 5, 195.
19. Kim, C.; Wang, Z.; Choi, H.-J.; Ha, Y.-G.; Facchetti, A.; Marks, T. J. J. Am. Chem. Soc.
2008, 130, 6867.
20. Li, W.; Wang, Q.; Cui, J.; Chou, H.; Shaheen, S. E.; Jabbour, G. E.; Anderson, J.; Lee, P.;
Kippelen, B.; Peyghambarian, N.; Armstrong, N. R.; Marks, T. J. Adv. Mater. 1999, 11, 730.
21. Li, J.; Marks, T. J. Chem. Mater. 2008, 20, 4873.
22. Morais, T. D. d.; Chaput, F.; Lahlil, K.; Boilot, J.-P. Adv. Mater. 1999, 11, 107.
23. Brook, M. A. Silicon in Organic, Organmetallic, and Polymer Chemistry; John Wiley &
Sons: New York, 2000.
24. Schaer, M.; Nüesch, F.; Berner, D.; Leo, W.; Zuppiroli, L. Adv. Func. Mater. 2001, 11, 116.
25. Kawano, K.; Pacios, R.; Poplavskyy, D.; Nelson, J.; Bradley, D. D. C.; Durrant, J. R. Solar
Energy Materials and Solar Cells 2006, 90, 3520.
26. Grande, J. B.; Fawcett, A. S.; McLaughlin, A. J.; Gonzaga, F.; Bender, T. P.; Brook, M. A.
Polymer 2012, 53, 3135.
27. Thelakkat, M. Macro. Mat. Engineering 2002, 287, 442.
28. Hartwig, J. F.; Kawatsura, M.; Hauck, S. I.; Shaughnessy, K. H.; Alcazar-Roman, L. M. J.
Org. Chem. 1999, 64, 5575.
29. Teetsov, J.; Anne Fox, M. J. Mater. Chem. 1999, 9, 2117.
119
119
30. Chen, W.-H.; Wang, K.-L.; Hung, W.-Y.; Jiang, J.-C.; Liaw, D.-J.; Lee, K.-R.; Lai, J.-Y.;
Chen, C.-L. J. Polym. Sci. A 2010, 48, 4654.
120
120
Personal Interest Projects 1: Design of Deep-Blue Emitting Materials for OLEDs
9.4 Executive Summary
This chapter has been previously published as a full paper in Organic Electronics.
Brett A. Kamino, Yi-Lu Chang, Zheng-Hong Lu and Timothy P. Bender (2012), Organic
Electronics, 13 (8), 1479-1485. Figure and Schemes are reprinted with permission. Copyright 2012 Elsevier
The work described in this paper does not relate to my primary thesis statement and the projects
previously discussed. However, this work did fit within the overall goals of our laboratory and
that of a close collaborator. Specifically, this goal was the design of new materials for organic
light emitting diodes with a particular focus on white lighting and display technology. When this
project began, I was very interested in learning more about this area of research that was being
actively pursued nearby. Because of this motivation, when the opportunity to study materials for
this project arose, I quickly took it up.
The genesis of this project relates very closely with the materials covered in Chapter 10. As a
prelude to the next chapter, we were very interested in designing new light absorbing materials
for organic solar cells that were related to boron subphthalocyanines. This material was
mentioned earlier in Chapter 4. While working on this project, I noticed that one of the precursor
materials had excellent photoluminescent properties with strong emission in the deep-blue part of
the spectrum. From this observation and several discussions with my co-author (Yi-Lu Chang)
we began this project.
9.5 Statement of Contributions
The authorship of this paper is as follows: Brett A. Kamino, Yi-Lu Chang, Zheng-Hong Lu,
Timothy P. Bender. This project was instigated by me and all compound synthesis and
characterization was performed by me. Yi-Lu Chang integrated my materials into a standard
OLED design and performed all device testing. Zheng-Hong Lu is Yi-Lu Chang’s supervisor and
all device work was performed in his laboratory. The paper was written primarily by me with
input from Yi-Lu Chang and Prof. Timothy P. Bender.
121
121
9.6 Paper
9.6.1 Abstract
Unprecedented phthalonitrile based fluorophores are reported and studied for incorporation into
organic light emitting diodes. The phthalonitriles were obtained using a very simple synthetic
procedure and were found to be highly fluorescent with quantum yields approaching unity; they
are also thermally stable and electrochemically active. When incorporated into OLEDs as
fluorescent dopants, the resulting devices have good device efficiencies and emit in the deep-
blue area of the spectrum with CIE coordinates that are close to the NTSC standard for blue.
9.6.2 Introduction
Organic light emitting diodes (OLEDs) are a promising technology for full-colour, large area
display technology.1 Such displays typically rely on the use of the red, green, blue (RGB) colour
space which requires separate emission from red, green, and blue materials/OLEDs. Currently,
highly efficient phosphorescent OLEDs emitting red and green light are well-known and can
achieve internal quantum efficiencies approaching unity. However, the development of high-
efficiency blue OLEDs with Commission Internationale de l’éclairage (CIE)2 coordinates
matching the NTSC colour standard for blue (CIEx = 0.14, CIEy = 0.08)3 has proven more
difficult and remains a current challenge for display technology. Blue phosphorescent devices
have been studied extensively and a number of nonsaturated blue or sky-blue devices are well
known.4,5 While high efficiencies have been achieved these technologies still have many
disadvantages for display technologies including poor colour saturation and extremely short
operational lifetimes.6 Improvements in colour saturation for these devices has recently been
developed through the engineering of better host materials7,8 and phosphorescent emitting
materials.9 These devices have impressive performance but phosphorescent devices are still
largely limited to CIEy coordinates of <0.15 and issues with the stability of high energy
phosphorescent emitters remain. Therefore, there is still room for further improvement in colour
saturation and stability by engineering materials that can more closely match the standard for
blue colour in display technology.
One alternative approach to this problem has been to combine blue fluorescent dopant with red
and green phosphorescent dopants to achieve full colour displays.10,11 While fluorescent blue
122
122
emitting materials are inherently less efficient due to only being able to harvest singlet
excitons/electron–hole pairs, they are better able to achieve deep-blue emission while
maintaining high photoluminescent efficiencies and chemical stability. Because of this, there is a
strong interest in developing high-efficiency, deep-blue fluorescent OLEDs that can approach the
NTSC colour standard for blue. In regards to material design however, there are relatively few
classes of materials that satisfy these requirements. The majority of these are based on a limited
number of structural themes, including: styrylbiphenyls,12-15 acenes,16,17 group XIII metal
complexes18 and phenylquinolines.19 Given this limited pool of deep-blue emitting groups, there
exists a need to identify additional molecular structures which emit deep-blue light. In this paper,
we disclose an unprecedented pair of highly-emissive phthalonitrile based blue emitters and
establish their utility in deep-blue OLED devices that closely match the NTSC standard for blue.
9.6.3 Results and Discussion
The inspiration for this study came from the description of 9-1 (Scheme 9-1) in a patent
concerning new phthalonitriles for the synthesis of phthalocyanines20 wherein no mention of the
fluorescent or other optical properties was included. Upon repeating the described synthesis, we
discovered that compound 9-1 was highly fluorescent even when photo-excited with a simple
laboratory UV lamp. We also decided to synthesize a structural variant in the form of compound
9-2 as the reagent was commercially available (Scheme 9-1). Both phthalonitriles contain an
extended π-electron system through two [1,4] benzodioxin linkages to yield highly conjugated
and planar compounds (as shown by DFT calculations, Figure 9-1).
Scheme 9-1. Synthetic pathways towards phthalonitriles 9-1 and 9-2.
123
123
HOMO
LUMO
LUMO
HOMO
Figure 9-1. Geometry optimized structure for (a) compound 9-1 (top) and (b) compound 9-2 (bottom) and their predicted HOMO and LUMO distributions.
The syntheses rely on nucleophilic aromatic substitution of tetrachlorophthalonitrile with the
appropriate aromatic 1,2-diol in dimethylformamide along with stoichiometric quantities of
potassium carbonate. Both syntheses proceeded rapidly and cleanly from commercially available
starting materials to produce the desired products in high yields. Purification was rapidly
achieved by simply filtering the pure product and washing with solvent. The resulting materials
were isolated as insoluble white powders and we did not detect the formation of regioisomers.
124
124
Despite the facile workup procedure, exceptionally high purities were achieved for both
compounds without the need for subsequent purification steps. Structural determination and
purity was achieved through elemental analysis and high-resolution mass spectrometry.
Additionally, 1H NMR of the compounds is reported. Unfortunately, the poor solubility of the
compounds inhibited us from acquiring 13C NMR data.
Table 9-1. Photophysical, electrochemical and thermal properties of compounds 1 and 2
Compound λmax
sol emission
(nm) a
λmax, film
emission (nm) Φsol (%) a,b
Eoxpeak
(onset)
(V)c
Eredpeak (V)c
EHOMOd
[calculated]
(eV)
ELUMOf
e[calculated]e
(eV)
Td (°C)g
9-1 410 421 ~1 1.76 (1.56) -1.62 -6.14
[-6.07] -2.93 [-2.14] 277
9-2 405 434 0.9 1.66 (1.53) - -6.11
[-6.02] -2.86 [-2.15] 396
a Measured in tetrahydrofuran; λexcitation = 340nm. b Measured relative to 9,10-diphenylanthracene in cyclohexane21 c Peak and onset potential versus Ag/AgCl. d Estimated from onset potential.22 e As determined from DFT calculations f Estimated from HOMO and optical bandgap. g Defined as 5% mass loss from TGA
125
125
Figure 9-2. Normalized absorption (black line) and emission spectra (solid color for solution,
dashed for thin film) of 9-1 (a) and 9-2 (b). Solution spectra were collected in THF.
The photophysical properties of each compound were explored through solution UV–VIS
absorbance and photoluminescence measurements in tetrahydrofuran (Figure 9-2). Additionally,
solid-state photoluminescence measurements were taken from vacuum deposited films. All of
this data is summarized in Table 9-1. From this data, we observe that each compound emits in
126
126
the deep-blue area of the spectrum in both solution and in the solid-state. Interestingly, both the
onset of absorbance and the solution emission peak for 1 are slightly red shifted compared to 9-2
(~5 nm) in solution. This is somewhat surprising considering the greater conjugation length of 9-
2 versus 1 which would normally facilitate the opposite trend as seen in a series of acenes (e.g.
benzene, naphthalene, anthracene). As well, ground-state conjugation throughout each structure
is confirmed by the DFT modelling results (Figure 9-1) further supporting this prediction. We
believe that this deviation from the expected behaviour may be due to the nature of conjugation
throughout each molecule. The presence of planar oxygen atoms in these structures leads to
hyperconjugation between the peripheral phenyl units and the central phthalonitrile core through
the oxygen atoms. This less than perfect delocalization across the structure may prevent the
expected lowering of the optical band gap between 9-1 and 9-2. That being said, we do not have
a more thorough understanding of this phenomenon at this time. Solid-state photoluminescence
shows moderate red shifting of the emission peak for each compound compared to solution
photoluminescence with the effect being greater for 9-2 than 9-1. This larger change in the
photoluminescent peak wavelength could be attributable to an increase in intermolecular
interactions in the solid state afforded by the greater degree of conjugation.
Relative fluorescent quantum yield measurements were performed in THF and referenced to
9,10-diphenylanthracene in a cyclohexane solution (Φyield ~ 0.9).21 The difference in solvents
was necessitated by the low solubility of 9-1 and 9-2 in cyclohexane. 9,10-Diphenylanthracene
was chosen as a reference as it has similar absorbance and emission wavelengths as our
compounds. Solutions were degassed prior to each experiment and sufficiently low
concentrations were used to minimize reabsorption errors. Both compounds are highly
photoluminescent with 9-1 having a quantum yield of near unity while 9-2 having a quantum
yield of 0.9. The high photoluminescent efficiencies were surprising as phthalonitriles are not
known to be particularly efficient fluorophores. To the best of our knowledge this is the first
example of a strongly fluorescent phthalonitrile derivatives.
In order to explore the potential of these compounds to be used as emitters in OLEDs, each was
characterized by solution electrochemical techniques and thermogravimetric analysis. The
electrochemical behaviour of 9-1 and 9-2 was determined through cyclic voltammetry in
dichloromethane with 0.1 M of tetrabutylammonium perchlorate as a supporting electrolyte.
127
127
Both compounds displayed fully irreversible oxidation waves with peak potentials at 1.76 and
1.66 V vs. Ag/AgCl for 9-1 and 9-2, respectively (Table 9-1). Additionally, an irreversible
reduction peak is observed for compound 1 at -1.62 V vs. Ag/AgCl while no clear reduction
activity was observed for 2. From this data, absolute molecular orbital energies were estimated22
from the onset oxidations waves for the HOMO energy, while the LUMO energy values were
estimated from the HOMO energy added to the energy of the optical bandgap (Table 9-1).
Most OLED layers are deposited using physical vapour deposition requiring candidate
compounds to possess some degree of thermal stability in order to be processed into devices. To
evaluate the compatibility of phthalonitriles 9-1 and 9-2 with modern OLED manufacturing
techniques, the thermal stability of each was measured using thermogravimetric analysis (TGA)
under N2 with a ramp rate of 10 °C/min. For compounds 9-1 and 9-2 we observed a 5% mass
loss at 277 and 396 °C (Table 9-1), respectively. A complete loss of initial mass was observed
for compound 1 indicating no formation of ash. This implies that the compound simply sublimed
upon heating. In the case of phthalonitrile 9-2, ash was formed and thus the 5% weight loss
indicates the onset of decomposition of the compound. Regardless of the nature of the 5% weight
loss, these relatively high values confirm the stability of these structural motifs and suggest that
they would be well-suited for physical vapour deposition.
Alluded to above, geometry optimized DFT calculations were performed not only to understand
the molecular shape and conformation of 9-1 and 9-2 but also to aid the understanding of
electronic structure of this structural motif. Because compounds 9-1 and 9-2 represent a
completely new class of fluorophore, an understanding of the electronic structure is important for
further elaboration on the molecular structure. Visualizations of the calculated HOMO and
LUMO are given in Figure 9-1. In each case, the HOMO is evenly distributed throughout the
entire conjugated structure of the molecules. In contrast, the LUMO is isolated to the
phthalonitrile core of each molecule. This distribution of orbital densities suggests that tuning of
the HOMO could easily be accomplished by the addition of electron donating groups to the
periphery of the molecules whereas little variation would be possible in the LUMO level.
Finally, each molecule was incorporated as a fluorescent dopant in a series of four simple OLED
devices23 at both 2 and 4 wt.% with respect to the host material (4,4`-di(9-carbazolyl)-biphenyl,
CBP) (Figure 9-3, Table 9-2). The device structure used was: ITO/MoO3/CBP (35 nm)/emitting
128
128
layer (15 nm)/TPBi (65 nm)/LiF (1 nm)/Al (100 nm) where the emitting layer is composed of the
fluorescent dopant and CBP (TPBi = 2,2`,2``-(1,3,5-benzinetriyl)tris(1-phenyl-1-H-
benzimidazole)). All four devices achieved deep-blue emission with CIE coordinates that are
exceptionally close to standard blue (CIEx = 0.14, CIEy = 0.08) with moderate luminance values
and good turn-on voltages (Figure 9-3). In particular, devices made using 9-1 showed blue
emission that comes very close to the ideal value with CIE coordinates of CIEx = 0.16, CIEy =
0.08 (for the 2 wt.% doped device at 100 cd/m2). Looking at the electroluminescent spectra for
compound 9-1 (Figure 9-3), we can conclude that there is almost exclusively emission from the
dopant with a small shoulder at wavelengths < 400 nm. For devices using 9-2 however,
significant emission occurred below 400 nm and a broadened peak shape was observed. This
shoulder is consistent with electroluminescence from the CBP host material24 and either implies
poor charge balance within the device, or inefficient energy transfer from the host to the dopant.
Moreover, when comparing the estimated energy levels of the fluorophores to that of the host
material (CBP) using the same methods as above, CBP has a significantly higher HOMO level at
-5.61 eV.25 This large mismatch in the HOMO energies of the host and guest may impede direct
energy trapping by the guest molecule resulting in endothermic energy transfer and ultimately
limit the efficiency of the devices. The observation that the electroluminescence from the host
material appears more prominent for compound 9-2 compared to compound 1 could be
attributable to the higher Elumo of -2.86 eV for compound 9-2 as compared to that of compound
9-1 (-2.93 eV, Table 9-1). This could lead to a lower capability for the CBP host to confine
charges to compound 9-2, leading to a higher probability of energy back transfer from the dopant
to the host thereby resulting in higher host emission.
129
129
Figure 9-3a. (i) Electroluminescent spectra of compound 9-1 (solid lines are for 2 wt% doping in the
emission layer and hashed lines are for 4 wt% doping) at 100 cd/m2; (ii) Current density (solid lines) and
luminance (hashed lines) as a function of voltage for devices using 2 wt% (black lines) and 4 wt% (red
lines) of compound 9-1 as a dopant in the emission layer; (iii) External quantum efficiency versus
luminance for devices using 2 wt% (black line) and 4 wt% (red line) compound 9-1 as a dopant in the
emission layer; (iv) Current efficiency (hashes lines) and power efficiency (solid lines) as a function of
current density in devices using 2 wt% (black lines) and 4 wt% (red lines) compound 9-1 as a dopant in
the emission layer. Device architecture for all devices is illustrated (Figure 9-3a(i), inset).
130
130
Figure 9-3b. (i) Electroluminescent spectra of compound 9-2 (solid lines are for 2 wt% doping in the
emission layer and hashed lines are for 4 wt% doping) at 100 cd/m2; (ii) Current density (solid lines) and
luminance (hashed lines) as a function of voltage for devices using 2 wt% (black lines) and 4 wt% (blue
lines) of compound 9-2 as a dopant in the emission layer; (iii) External quantum efficiency versus
luminance for devices using 2 wt% (black line) and 4 wt% (blue) compound 9-2 as a dopant in the
emission layer; (iv) Current efficiency (hashes lines) and power efficiency (solid lines) as a function of
current density in devices using 2 wt% (black lines) and 4 wt% (blue lines) compound 9-2 as a dopant in
the emission layer. Device architecture for all devices is illustrated (Figure 9-3a(i), inset).
131
131
Table 9-2. Performance of OLEDs incorporating 1 and 2 as dopants
Compound Concentration
(wt%) Vturn on (V)a EQEmax (%) λmax
EL (nm) b CIExb CIEy
b
9-1 2 3.4 2.14 434 0.16 0.08
4 3.4 2.12 440 0.16 0.09
9-2 2 3.8 1.66 434 0.16 0.11
4 3.8 1.90 444 0.16 0.12
a As defined by a luminance of >0.5 cd/m2. b Determined at a luminance of 100 cd/m2
Despite the potential challenges in device optimization, these initial prototype devices performed
admirably well. A maximum external quantum efficiency of 2.14% was observed for the 2 wt.%
doped device with compound 9-1 while devices made with compound 9-2 showed slightly lower
values with a maximum of 1.90%. Both values are extremely promising and we anticipate that
further engineering of the devices and the compounds themselves can yield even higher
performance. Lifetime measurements were prevented by the low morphological stability of the
host material, CBP with low glass transition temperature of 62 °C.26 Future development of more
stable hosts and transport layers are in progress to study device life times.
9.6.4 Conclusions
In summary, we have synthesized and characterized two novel phthalonitrile based fluorophores
for use in deep blue OLEDs that approach the NTSC standard for blue. The compounds possess
many ideal qualities for use in OLED devices including good emission coordinates/colour and
thermal stability. When incorporated into prototype OLEDs, these compounds undergo
electroluminescence with high external efficiencies and a colour near the NTSC standard for
blue. The high efficiency and good colour rendering of these compounds suggests that they may
be a promising material for application in a full colour OLED display.
9.7 References
1. Forrest, S.R., Nature 2004, 428, 911.
2. CIE Commission Internationale de l’Eclairage Proceedings,Cambridge University Press:
Cambridge, 1932.
132
132
3. D.G. Fink, Color Television Standards: Selected Papers and Records, McGraw-Hill, New
York, 1955.
4. Sasabe, H.; Gonmori, E.; Chiba, T.; Li, Y.-J.; Tanaka, D.; Su, S.-J.; Takeda, T.; Pu, Y.-J.;
Nakayama, K.-I.; Kido, J. Chem. Mater. 2008, 20, 5951.
5. Chopra, N.; Lee, J.; Zheng, Y.; Eom, S,-H.; Xue, J.; So, F. Appl. Phys. Lett 2008, 93,
143307.
6. Moraes, I.R.D.; Scholz, S.; Lussem, B.; Leo, K. Org. Electron. 2011, 12, 341.
7. Jeon, S.O.; Yook, K.S.; Joo, C.W.; Lee, J.Y. Adv. Mater. 2010, 22, 1872.
8. Jeon, S.O.; Jang, S.E.; Son, H.S.; Lee, J.Y. Adv. Mater. 2011, 23, 1411-1436.
9. Sasabe, H.; Takamatsu, J.; Motoyama, T.; Watanabe, S.; Wagenblast, G.; Langer, N.;
Molt, O.; Fuchs, E.; Lennartz, C.; Kido, J. Adv. Mater. 2010, 22, 5003.
10. Sun, Y.; Giebink, N.C.; Kanno, H.; Ma, B.; Thompson, M.E.; Forrest, S.R. Nature 2006,
440, 908.
11. Rosenow, T.C.; Furno, M.; Reineke, S.; Olthof, S.; Lussem, B.R.; Leo, K. J. Appl. Phys.
2010, 108, 113113.
12. Lee, M.T.; Liao, C.H.; Tsai, C.H.; Chen, C.H. Adv. Mater. 2005, 17, 2493.
13. Ho, M.-H.; Wu, Y.-S.; Wen, S.-W.; Chen, T.-M.; Chen, C.H. Appl. Phys. Lett. 2007, 91,
083515.
14. Kim, S.-K.; Yang, B.; Ma, Y.; Lee, J-H.; Park, J.-W. J. Mater. Chem. 2008, 18, 3376.
15. Kim, S.O.; Lee, K.H.; Kim, G.Y.; Seo, J.H.; Kim, Y.K.; Yoon, S.S. Synth. Met. 2010, 160,
1259.
16. Ho, M.-H.; Wu, Y.-S; Wen, S.-W.; Lee, M.-T.; Chen, T.-M.; Chen, C.H.; Kwok, K.-C.;
So, S.-K.; Yeung, K.-T.; Cheng, Y.-K.; Gao, Z.-Q. Appl. Phys. Lett. 2006, 89, 252903.
133
133
17. Tao, S.; Zhou, Y.; Lee, C.-S.; Zhang, X.; Lee, S.-T. Chem. Mater. 2010, 22, 2138.
18. Liao, S.-H.; Shiu, J.-R.; Liu, S.-W.; Yeh, S.J.; Chen, Y.-H.; Chen, C.-T.; Chow, T.J.; Wu,
C.-I. J. Am. Chem. Soc. 2009, 131, 763.
19. Lee, S.J.; Park, J.S.; Yoon, K.-J.; Kim, Y.-I.; Jin, S.-H.; Kang, S.K.; Gal, Y.-S.; Kang, S.;
Lee, J.Y.; Kang, J.-W.; Lee, S.-H.; Park, H.D.; Kim, J.-J. Adv. Func. Mater. 2008, 18,
3922.
20. Gregory, P.; Reynolds, S.J. US Patent 6,335,442, 2002.
21. Eaton, D.F.; Pure. Appl. Chem. 1988, 60, 1107.
22. Cardona, C.M.; Li, W.; Kaifer, A.E.; Stockdale, D.; Bazan, G.C. Adv. Mater. 2011, 23,
2367.
23. Wang, Z.B.; Helander, M.G.; Qiu, J.; Puzzo, D.P.; Greiner, M.T.; Liu, Z.W.; Lu, Z.H.
Appl. Phys. Lett. 2011, 98, 073310.
24. Zou, L.; Savvate’ev, V.; Booher, J.; Kim, C.H.; Shinar, J. Appl. Phys. Lett. 2001, 79,
2282.
25. Hu, D.; Lu, P.; Wang, C.; Lie, H.; Wang, H.; Wang, Z.; Fei, T.; Gu, X.; Ma, Y. J. Mater.
Chem. 2009, 19, 6143.
26. Xiao, L.; Chen, Z.; Qu, B.; Luo, J.; Kon, S.; Gong, Q.; Kido, J. Adv. Mater. 2011, 23, 926.
134
134
Chapter 10: Personal Interest Projects 2: Colour Tuning Boron Subphthalocyanine
10.1 Executive Summary
This chapter represents a draft of a paper that is intended to be submitted to Chemical
Communications.
As with Chapter 9, the work described heirin does not relate to my primary thesis statement.
However, the contents of this project were of great interest to me and are intimately related to
other objectives in our laboratory. In this paper, I’ve synthesized and characterized a number of
new boron subphthalocyanine (BsubPc) derivatives with drastically altered photophysical and
electrochemical properties compared to base materials. These compounds are based on the π-
extended phthlaonitrile derivatives disclosed in Chapter 9. This work represents one of the few
published methods to tune BsubPc derivatives over a wide range and complements other
materials developed within the laboratory. Materials discussed in this chapter will hopefully go
on to be incorporated into organic photovoltaic devices in the future.
10.2 Statement of Contributions
The author list of this paper draft is as follows: Brett A. Kamino, Timothy P. Bender
The concept of this work and the design of experiments were done solely by me. All synthesis,
purification and characterization of these materials was done solely by me. The paper was
written primarily by me with input from Prof. Tim Bender.
10.3 Paper
10.3.1 Body
First reported in 1972 by Meller and Ossko,1 boron subphthalocyanine2 (BsubPc) is a ring
contracted cousin of the well-known family of phthalocyanine dyes and pigments. BsubPcs are
characterized by a striking magenta color, strong orange fluorescence, and a unique bowl-like
molecular shape. Beyond their basic molecular properties, they have recently received a great
deal of attention for their application as functional organic materials in non-linear optics,3 and a
variety of organic electronic devices including organic field-effect transistors (OFETs),4 organic
135
135
light emitting diodes (OLEDs)5 and organic photovoltaics (OPVs). As an electron donor layer in
OPVs, BsubPcs have been shown to pair well with C60 as an electron acceptor layer, producing
devices with efficiencies up to 5.4%.6 As well, BsubPcs7 and their halogenated derivatives8 have
also been shown to work effectively as electron acceptor layers in OPVs. The unique properties
of BsubPcs, their flexible roles within a number of organic electronic devices of BsubPcs and
their auspicious performance warrants further investigation into their development as functional
materials.9
Engineering of BsubPcs to further improve device performance requires the development of new
synthetic tools and strategies to allow for the tailoring of molecular structure and the resulting
optoelectronic properties. Specifically, altering their electrochemical properties and their
absorption and interaction with light of varying wavelenghts is desirable. Several strategies to
achieve variations in the optoelectronic properties of BsubPcs have been reported. These
methods include simple peripheral substitution of the isoindoline units which comprise the
BsubPc itself,10 and the dimerization of the BsubPc either with itself11 or with other
chromophores.12 However, the most dramatic method to alter the basic properties of BsubPcs has
been in modification of the core macrocyclic subPc fragment through the use of modified
phthalonitrile-type precursors. This can be accomplished either by incorporating modified
phthalonitriles symmetrically around the ring13 or through the use of mixtures of different
phthalonitriles during synthesis. The mixed phthalonitrile approach results in the formation of a
statistical mixture of products from which individual compounds can often be difficult to isolate
in anything other than a low yield.14 Despite this, in each case the use of modified or mixed
phthalonitriles has been shown to greatly alter the optoelectronic properties of the resulting
BsubPcs. Widespread exploration of this strategy has been limited due to a lack of phthalonitrile
precursor materials which are easily prepared.
The synthesis of phthalonitriles 10-1 and 10-2 have been previously described by Gregory in the
patent literature, along with the preparation of zinc phthalocyanines from each .15 Phthalonitriles
10-1 and 10-2 are made from the reaction of tetrachlorophthalonitrile with catechol or 3,5-di-t-
butylcatechol (respectively, Scheme 10-1) in DMF at moderate temperatures. The reaction is
surprisingly selective and the workup is facile. We have previously shown that phthalonitrile 10-
1 is itself an efficient deep-blue light emitter when incorporated into OLEDs.16 What is unique
136
136
about phthalonitrile 10-1 is that it contains a π extended system despite the presence of the four
sp3 oxygen atoms. Using DFT modeling we have shown that the HOMO of phthalonitrile 10-1 is
equally distributed throughout the molecule while having density resident on the oxygen atoms.
The extended conjugation is further evident in the significantly red-shifted λmax of phthalonitrile
10-1 from that of phthalonitrile itself.16 Moreoever, the zinc phthalocyanines reported by
Gregory have a λmax 80-95 nm red shifted compared to standard zinc phthalocyanine.15
Scheme 10-1: Synthesis of π extended BsubPcs 10-3a-b and 10-4a-c and their precursor
phthalonitriles.
10-1 10-2
10-3a
10-3b
10-4a: X = H 10-4b: X = F 10-4c: X = Cl
137
137
In our laboratory, symmetrically substituted BsubPcs 10-3a and 10-3b were obtained by a
standard cyclotrimerization reaction of phthalonitrile 10-1 with BCl3 followed by axial
substitution by 4-t-butylphenol (10-3a) or pentafluorophenol (10-3b, Scheme 10-1).17 Attempts
to use BBr3 in the cyclotrimerization reaction were unsuccessful, likely due competitive ether
cleavage by BBr3 of a molecular system enabled for SNAr reactions. The resulting BsubPcs 10-3a
and 10-3b were isolated as dark green powders in comparable yields to that of typical BsubPcs.
Their respective identity and purity was established using 1H, 11B, 19F NMR, low molecular
weight GPC, and HRMS. Single crystals of 10-3b solvated with THF were grown and the
structure solved by x-ray diffraction. Analysis confirms not only the molecular structure of
BsubPc 10-3b but that it retains the bowl shaped configuration typical of a normal BsubPc with
minimal distortion from the π-extension (Figure 10-1a).
Owing to the successful synthesis of the symmetrically substituted BsubPcs (10-3a-b), the
reaction of 10-1 mixed with unmodified phthalonitrile under the same reaction conditions was
performed. As expected, analysis of the reaction mixture by low molecular weight SEC and
HPLC revealed a statistical mixture of compounds including regular Cl-BsubPc, the axially
chlorinated intermediate to 10-3a and 10-3b and a number of compounds with various
absorbance profiles indicative of BsubPcs and with varying molecular sizes. Unfortunately, this
mixture proved recalcitrant to separation using a number of different purification strategies.
Chromatographic separation techniques consistently resulted in co-elution of a number of the
components including unreacted phthalonitrile 10-1, a common issue with the separation of these
types of materials.18
(a)
138
138
(b)
Figure 10-1: Thermal ellipsoid plot of (a) 10-3b·(THF)2 (CCDC deposition 910746) and (b)
10-4a·(CHCl3)2 (CCDC deposition 910747). Thermal ellipsoids are set at the 50% probability
level. Hydrogen atoms and included solvent have been omitted for clarity. Colors: boron – pink;
nitrogen – blue; carbon – grey; oxygen – red; fluorine – magenta.
In an effort to circumvent the isolation issue and obtain unsymmetrically substituted BsubPcs,
phthalonitrile 10-2 containing four t-butyl groups was synthesized. It was hypothesized that the
substantially increased steric bulk of the phthalonitrile would prevent the formation of BsubPcs
entirely derived from phthalonitrile 10-2 (homo-cyclotrimerization). Thus, simplifying the
mixture of products produced when used in a mixture with phthalonitrile. As well, we felt the
presence of t-butyl groups would assist in separation of the final products and prevent co-elution
of products upon chromatographic separation.
Simple molecular mechanics calculations were performed on the hypothetical BsubPc made
entirely from phthalonitrile 10-2.This structure was found to have significant distortions from
planarity within the BsubPc ring system caused by steric crowding of neighboring dioxy-t-butyl-
phenylene fragments. Therefore the overall molecule would have an unreasonable amount of
steric strain and likely not be stable.
Phthalonitrile 10-2 was isolated as a mixture of three structural isomers. Using high-field 1H
NMR spectroscopy (700 MHz), the three isomers of 10-2 were positively identified and their
139
139
relative abundance was established (see section 12.8.3). Phthalonitrile 10-2 was placed alone
under standard reaction conditions with BCl3 and indeed no BsubPc products were detected by
HPLC (Scheme 10-1).
When cyclotrimerizations where performed with a mixture of phthalonitrile 10-2 (component A)
and either phthalonitrile, tetrafluorophthalonitrile, or tetrachlorophthalonitrile (component B), a
mixture of regular Cl-BsubPc, one major and one minor product were observed using low
molecular weight GPC analysis with a photodiode array detector. Each product were found to
have a red shifted absorption spectrum with a profile similar to normal BsubPc. The crude
mixture from each reaction was reacted with pentafluorophenol under standard conditions
(Scheme 10-1) and a single product (AB2) was successfully isolated from the reaction mixture by
chromatography over silica gel. The purity of this product was determined by the presence of a
single spot on TLC and a single peak using low molecular weight GPC analysis. Because
phthalonitrile 2 is a mixture of three isomers, the new BsubPc products are also expected to exist
as a mixture of structural isomers. Indeed this was found to be the case for 10-4a and 10-4c
(determined by 1H NMR spectroscopy). Surprisingly, product 10-4b was isolated as a single
structural isomer. It is not known why this particular isomer was able to be isolated. A small
amount of a single isomer of 10-4a was isolated by vapour diffusion crystallization. The crystals
proved suitable for x-ray diffraction and on analysis confirmed the structure of 10-4a (as its
chloroform solvate, Figure 10-1b).
140
140
(a)
(b)
Figure 10-2: Normalized UV-Vis absorbance spectra of (a) F5BsubPc, 10-4a and 10-3b and (b)
10-4a-c.
10-4a
10-3b
141
141
Presumably due to the large difference in polarity afforded by the t-butyl groups, the desired
products 10-4a-c were easily separated from regular pentafluorophenoxy-BsubPc (F5BsubPc)
made up of only phthalonitrile (B3). The second minor product with red shifted absorption was
found to have a larger molecular size (by GPC analysis) and a small red-shift in its absorption
spectrum relative to 10-4a-c. We suspected that this was the product made up of two π-extended
phthalonitriles 10-2 and a single phthalonitrile (A2B). However, we could not isolate this minor
product by chromatography over silica gel. It appeared to degrade on-column and despite
multiple attempts we could not observe the compound eluting. For the A2B system, simple
molecular mechanics calculations show steric repulsion between the adjacent t-butyl groups
resulting in a distortion of the dioxy-t-butyl-phenylene fragment from planarity. This effect is
similar to that seen in the A3 system, albeit not to the same level. This would seem to support the
experimental observations of poor chemical stability of the minor A2B product.
Each new BsubPc was characterized by UV-Vis absorbance spectroscopy and cyclic
voltammetry. Solution absorbance spectra (Figure 10-2, Table 10-1) show that incorporation of
phthalonitriles 10-1 and 10-2 are effective in red-shifting the absorbance of the base
chromophore relative to a reference BsubPc compound: F5BsubPc (Figure 10-2).5d BsubPcs 10-
3a and 10-3b possess an intense Q-band with a similar shape to F5BsubPc but red-shifted
approximately 100 nm to a λmax of 662 nm (Figure 10-2a) approximately equivalent to that of
boron subnaphthalocyanine (λmax = 663 nm).13b Large extinction coefficents were also measured
(ε = 9.5 x 105 L mol-1 cm-1 for 10-3a and 8.3 x 105 L mol-1 cm-1 for 10-3b) which are in the range
of typical BsubPcs and one order of magnitude higher than that reported for boron
subnaphthalocyanine (ε = 7.94 × 104 L mol-1 cm-1).13b Compound 10-4a, containing only a single
π-extended ligand, shows a smaller red shift in the Q-band of 48 nm. The other non-symmetric
BsubPcs (10-4b and 10-4c) also display broadened and red-shifted Q-bands which are found at a
λmax of 625 nm and 631 nm, respectively. Extinction coefficients for BsubPcs 10-4a-c were
smaller in magnitude than 10-3a-b, and were found to be between 4.4 x 105 L mol-1 cm-1 and 6.1
x 105 L mol-1 cm-1. Photoluminescent spectra for each compound were also obtained, but in all
cases only very weak fluorescence signals were detected.
142
142
Table 10-1: Calculated and experimentally determined properties of compounds F5BsubPc, 10-
3a-b and 10-4a-c.
Compound λmax
(nm)b ε x 105 (L
mol-1 cm-1)b λPL
(nm)b E1/2
ox
(mV)c,d E1/2
red 1 (mV ) c,d
[E1/2red 2 (mV)]
EHOMOcalc
(eV) ELUMO
calc (eV)
F5BsubPc 561 9.0 592a N/A -878a -5.31a -2.59a
10-3a 652 9.5 664 839 -935 -4.62 -2.34
10-3b 659 8.3 671 877 -886 -4.77 -2.47
10-4a 609 6.1 626 989 -990 -4.95 -2.50
10-4b 625 4.4 672 1163 -655 [-1263] -5.29 -3.04
10-4c 631 5.3 680 1197 -560 [-1255] -5.41 -3.17
a - data taken from Morse et al.5d, b data collected in THF solution, c data collected in DCM solution, d potentials referenced to
Ag/AgCl
The electrochemistry of 10-3a-b and 10-4a-c was explored by solution cyclic voltammetry in
DCM with 0.1M tetrabutylammonium perchlorate as the electrolyte and decamethylferrocene as
an internal reference19 (see section 12.10 for full voltammograms). Under these conditions, each
compound was found to undergo reversible oxidation and reduction reactions. The oxidative
behaviour of 10-3a-b and 10-4a-c was fairly typical for BsubPc derivatives. However, the
partially fluorinated and chlorinated (10-4b and 10-4c) BsubPcs each displayed two reversible
reductions (Figure 10-3). Typical BsubPcs rarely show reversible reductions5c and 10-4b-c are
the first known examples of a BsubPc derivative to undergo two reversible reductions. We may
therefore conclude that the BsubPcs reported herein have superior electrochemical stability when
compared to most other BsubPc derivatives. Additionally, throughout this series of BsubPcs, a
significant range of oxidation and reduction potentials can be achieved depending on the number
and type of phthalonitriles used in their syntheses.
143
143
Figure 10-3: Cyclic voltammogram of BsubPc compound 10-4b in DCM with 0.1M
tetrabutylammonium perchlorate and decamethylferrocene as an internal standard.
The increased electrochemical stability and the trends seen in the UV-Vis absorbance spectra
were further investigated using geometry optimized DFT calculations (see section 12.9). For the
symmetric BsubPcs (10-3a and 10-3b), both the HOMO and LUMO are spread out over the
entire bowl structure. From this, we can presume that the increase in electrochemical stability is
due to increased delocalization of charge throughout the extended π conjugated structure
effectively stabilizing the radical cation/anion. For the non-symmetric products (10-4a-c), the
HOMO is distributed evenly throughout the bowl structure while the LUMO is mostly localized
over the isoindoline units originating from the normal phthalonitrile and the boron centre. This
partial charge separation between the two halves of the bowl is reminiscent of donor-acceptor
chromophores where the optoelectronic properties can be tuned by altering the strength of the
electron donors/acceptors.20
This argument is supported by the change in position of the Q-band on increasing of the electron
withdrawing potential of the isoindoline units (compounds 10-4a-c, Figure 10-2b). As we go
from hydrogen to strong electron withdrawing substituents (-H < -F < -Cl), we see a narrowing
in the band gap as indicated by a red-shift in the absorption spectrum of the material. This is a
144
144
characteristic sign of an electron push-pull or donor-acceptor electronic system. To the best of
our knowledge, this is first example of a push-pull system within the conjugated bowl structure
of a BsubPc derivative. The intra-bowl push-pull system also greatly alters the electrochemical
oxidation/reduction potentials. Comparing F5BsubPc, 10-4a, and 10-3b which have 0, 1, or 3
electron rich isoindoline units, we observe an increase in reduction potential with increasing
electron density (Table 10-1). Similarly, comparing compounds 10-4a-c, we observe a lowering
of reduction potential and an increase in oxidation potential with stronger electron withdrawing
fragments. Thus, we can state that altering the electron donating or electron withdrawing
potentials of isoindoline units with the bowl of a BsubPc can be an effective tool in tuning not
only the band gap of the material but also its electrochemical potentials.
In summary, we have synthesized and characterized a series of π-extended BsubPc derivatives
using two electron rich π extended phthalonitrile precursors (phthalonitriles 10-1 and 10-2). The
resulting BsubPcs all display exceptional electrochemical stability as well as intense, red-shifted
absorbance spectra relative to normal BsubPcs. We have also synthesized a series of BsubPcs
from mixtures of phthalonitrile 10-2 with normal phthalonitriles and demonstrated that these
same properties can be readily tuned by varying the stoichiometry of the π-extended
phthalonitrile 10-2 and normal phthalonitriles. By setting up an intra-bowl push-pull system
within an unsymmetric BsubPcs, the optoelectronic properties can effectively be fine-tuned
across a range of absorption wavelengths and oxidation and/or reduction potentials.
10.3.2 References
1. Meller, A.; Ossko, A., Monatsh. Chem. 1972, 103 (1), 150-155.
2. Claessens, C. G.; Gonzalez-Rodriguez, D.; Torres, T., Chem. Rev. 2002, 102, 835-853.
3. (a) Dini, D.; Vagin, S.; Hanack, M.; Amendola, V.; Meneghetti, M., Chem. Comm. 2005,
(30), 3796-3798; (b) Claessens, C. G.; González-Rodríguez, D.; Torres, T.; Martín, G.;
Agulló-López, F.; Ledoux, I.; Zyss, J.; Ferro, V. R.; García de la Vega, J. M., J. Phys. Chem.
B 2005, 109 (9), 3800-3806.
4. Yasuda, T.; Tsutsui, T., Mol. Cryst. Liq. Cryst. 2006, 462 (1), 3-9.
145
145
5. (a) Díaz, D. D.; Bolink, H. J.; Cappelli, L.; Claessens, C. G.; Coronado, E.; Torres, T.,
Tetrahedron Lett. 2007, 48 (27), 4657-4660; (b) Helander, M. G.; Morse, G. E.; Qiu, J.;
Castrucci, J. S.; Bender, T. P.; Lu, Z.-H., ACS Appl. Mater. Interfaces 2010, 2 (11), 3147-
3152; (c) Morse, G. E.; Castrucci, J. S.; Helander, M. G.; Lu, Z.-H.; Bender, T. P., ACS Appl.
Mater. Interfaces 2011, 3 (9), 3538-3544; (d) Morse, G. E.; Helander, M. G.; Maka, J. F.; Lu,
Z.-H.; Bender, T. P., ACS Appl. Mater. Interfaces 2010, 2 (7), 1934-1944.
6. (a) Mutolo, K. L.; Mayo, E. I.; Rand, B. P.; Forrest, S. R.; Thompson, M. E., J. Am. Chem.
Soc. 2006, 128 (25), 8108-8109; (b) Pandey, R.; Holmes, R. J., Adv. Mater. 2010, 22 (46),
5301-5305; (c) Pandey, R.; Zou, Y.; Holmes, R. J., Appl. Phys. Lett. 2012, 101 (3), 033308.
7. Beaumont, N.; Cho, S. W.; Sullivan, P.; Newby, D.; Smith, K. E.; Jones, T. S., Adv. Func.
Mater. 2012, 22 (3), 561-566.
8. (a) Gommans, H.; Aernouts, T.; Verreet, B.; Heremans, P.; Medina, A. s.; Claessens, C. G.;
Torres, T., Adv. Func. Mater. 2009, 19 (21), 3435-3439; (b) Sullivan, P.; Duraud, A.; Hancox,
l.; Beaumont, N.; Mirri, G.; Tucker, J. H. R.; Hatton, R. A.; Shipman, M.; Jones, T. S., Adv.
Energy Mater. 2011, 1 (3), 352-355.
9. Morse, G. E.; Bender, T. P., ACS Appl. Mater. Interfaces 2012, 4 (10), 5055-5068.
10.(a) del Rey, B.; Keller, U.; Torres, T.; Rojo, G.; Agulló-López, F.; Nonell, S.; Martí, C.;
Brasselet, S.; Ledoux, I.; Zyss, J., J. Am. Chem. Soc. 1998, 120 (49), 12808-12817; (b)
González-Rodríguez, D.; Torres, T.; Guldi, D. M.; Rivera, J.; Herranz, M. Á.; Echegoyen, L.,
J. Am. Chem. Soc. 2004, 126 (20), 6301-6313.
11.(a) Yamasaki, Y.; Mori, T., Bull. Chem. Soc. Jpn. 2011, 84 (11), 1208-1214; (b) Eckert, A.
K.; Rodríguez-Morgade, M. S.; Torres, T., Chem. Comm. 2007, (40), 4104; (c) Claessens, C.
G.; Torres, T., Angew. Chem. Int. Ed. 2002, 41 (14), 2561-2565; (d) Fukuda, T.; Stork, J. R.;
Potucek, R. J.; Olmstead, M. M.; Noll, B. C.; Kobayashi, N.; Durfee, W. S., Angew. Chem.
Int. Ed. 2002, 41 (14), 2565-2568.
12.(a) Xu, H.; Ng, K. P., Inorg. Chem. 2008, 47, 7921-7927; (b) Zhao, Z.; Cammidge, A. N.;
Cook, M. J., Chem. Comm. 2009, (48), 7530; (c) Mauldin, C. E.; Piliego, C.; Poulsen, D.;
146
146
Unruh, D. A.; Woo, C.; Ma, B.; Mynar, J. L.; Fréchet, J. M. J., ACS Appl. Mater. Interfaces
2010, 2 (10), 2833-2838.
13.(a) Shimizu, S.; Miura, A.; Khene, S.; Nyokong, T.; Kobayashi, N., J. Am. Chem. Soc. 2011,
133 (43), 17322-17328; (b) Nonell, S.; Rubio, N.; del Rey, B.; Torres, T., J. Chem. Soc.
Perkin Trans. 2 2000, (6), 1091-1094.
14.(a) Shimizu, S.; Otaki, T.; Yamazaki, Y.; Kobayashi, N., Chem. Comm. 2012, 48 (34), 4100;
(b) Shimizu, S.; Nakano, S.; Hosoya, T.; Kobayashi, N., Chem. Comm. 2011, 47 (1), 316; (c)
Zhu, H.; Shimizu, S.; Kobayashi, N., Angew. Chem. Int. Ed. 2010, 49 (43), 8000-8003; (d)
Zyskowski, C. D.; Kennedy, V. O., J. Porphyrins Phthalocyanines 2000, 4, 707-712.
15.Gregory, P.; Reynolds, S. J. Phthalocyanines. US 6335442 B1, 2002.
16.Kamino, B. A.; Chang, Y.-L.; Lu, Z.-H.; Bender, T. P., Org. Electron. 2012, 13 (8), 1479-
1485.
17.Morse, G. E.; Paton, A. S.; Lough, A.; Bender, T. P., Dalton Trans. 2010, 39 (16), 3915.
18.González-Rodríguez, D.; Claessens, C. G.; Torres, T., J. Porphyrins Phthalocyanines 2009,
13 (02), 203-214.
19.(a) Noviandri, I.; Brown, K. N.; Fleming, D.S.; Fulvas, P.T.; Lay, P.A.; Masters, A.F.;
Philips, L. J. Phys. Chem. B 1999, 103, 6713. (b) Bender, T. P.; Graham, J. F.; Duff, J. M.,
Chem. Mater. 2001, 13 (11), 4105-4111.
20.Meier, H., Angew. Chem. Int. Ed. 2005, 44 (17), 2482-2506.
147
147
Chapter 11: Concluding Remarks and Future Work
11.1 Summary
In summary, we have explored various ways to alter the physical properties of organic
semiconductors without adversely affecting their basic electrochemical properties. These studies
have all focused on arylamine based compounds which are derivatives of well-known
compounds used throughout the literature.
This began with a study where we produced a series of triarylamine based compounds with a
wide range of structures and electrochemical properties. The photoinduced electron transfer
reaction with a fluorescent electron acceptor was studied to determine the effects of triarylamine
structure on its potential use in a organic photovoltaic cell. From this study we can conclude that
the actual structure of a triarylamine is unimportant when studying this specific process. The
efficiency of this electron transfer reaction was almost entirely determined by the
thermodynamics of the system studied.
The primary objective of this thesis was to alter the physical properties of arylamines so that they
would be freely flowing liquids at room temperature. We have shown two successful strategies
to accomplish this: the use of bulky silyl ether groups which can be installed with conventional
chemistry and the use of oligosiloxane groups which can be installed with the Piers-Rubinsztajn
reaction. Using bulky silyl ether groups was moderately successful on single triarylamine
substrates. We were able to generate materials which had glass transition temperatures well
below room temperature and in one case a free flowing liquid triarylamine. However, when
applied to larger substrates, this strategy failed to prevent crystallization and to lower the glass
transition low enough to allow for liquid materials. Despite this, we showed that this
modification strategy had a very minor impact on the useful electrochemical properties of the
base materials. As well, time-of-flight photocurrent mobility measurements on a liquid
triarylamine in this series confirms that these materials retain their favourable charge
transporting properties. Analysis of these results reveals that the charge transport behavior
through this liquid organic semiconductor is similar to what is found in conventional materials as
well.
148
148
Our second strategy to develop liquid organic semiconductors involved the novel application of a
Si-H activation chemistry known colloquially as the Piers-Rubinsztajn reaction. This synthetic
strategy allowed the use of readily available silanes and easily-purified methoxy functionalized
triarylamines as substrates. This chemistry resulted in the development of a wide library of
various triaryalmine structures, many of which are freely flowing liquids at room temperature.
And, much like the triarylamines functionalized with silyl ether groups, these materials all
displayed very predicatable electrochemical behavior. Uniquely, we have shown that some
substrates functionalize very poorly with this chemistry due to a non-productive outer-sphere
charge transfer reaction between highly electron rich triarylamines substrates and the very
electron poor borane catalyst. Despite this, the chemistry remains usable on a wide range of
different substrates.
This synthetic strategy was also extended beyond making liquid triaryalmines. By using cyclic
ethers instead of alkoxides as reaction partners, it is shown that cross-linked films can also be
synthesized by this Piers-Rubinsztajn chemistry. In a proof of concept experiment, we have
shown that triarylamines can be easily cross-linked into amorphous, glassy films with low
catalyst loadings. Much like we observed for the liquid triaryalmines, the glassy films seem to
retain their electrochemical properties despite the change in physical state.
Finally, two side projects were pursued: the synthesis of novel deep-blue fluorescent emitters for
OLEDS and the synthesis of boron subphthalocyanines with varied optoelectronic properties.
Novel deep-blue fluorescent emitters for OLEDs were explored by using a very simple synthesis
of π-extended phthalonitriles. These structures were shown to be highly fluorescent and non-
optimized OLEDs using them as functional elements displayed moderate efficiencies and
excellent colour renderings close to NTSC standards for blue displays. Using these same
phthalonitrile type materials, new boron subphthalocyanine derivatives were synthesized which
displayed widely tuneable electrochemical and photophysical properties. We show that by
combining these electron-rich phthalonitriles with electron poor phthalonitriles can allow fine-
tuning of the optical bandgap to produce multi-coloured subphthalocyanine derivatives. As well,
highly-stable electrochemistry was observed of a wide range suggesting that such materials may
have a future in organic electronic devices.
149
149
To put this work in a bit of perspective, the overall goal and theme of this work was really to
explore how far the physical properties of organic semiconductors could be altered and
engineered. As previously stated throughout this document, basically all organic semiconductors
in the literature are designed to be high glass transition temperature amorphous solids or highly
crystalline solids. The work in this thesis differentiates inself from other semiconductor
development because we are interested in materials with low glass transition temperatures and
minimized intermolecular interactions.
While current semiconductor designs have indeed been successful for a variety or applications,
they can be lacking in certain instances. The most important area where current materials fail is
in the development of flexible and elastomeric devices. Flexible and stretchable devices are a
talking point on almost any introductory slide about organic electronics. And indeed, given the
promise of numerous applications of such devices, this is a laudable goal. However, it is
somewhat irritating and suprising that no one ever botheedr to think about designing active layer
materials with flexibility or stretchability in mind. Proof of concept demonstrations of such
devices in the literature ultimately rely on building conventional devices on flexible or
elastomeric substrates. This approach is ultimately limited as brittle and crystalline materials can
crack or delaminate under physical strain. I believe that it is clear that further development
towards flexible or stretchable device will require a focus on improving the active layer materials
used with an emphasis on their physical properties.
The materials developed in this thesis including the liquid and near elastomeric materials were
designed to overcome these problems by virtue of the materials being inherently able to respond
to physical stress in a nondestructive manner. One can imagine bending an organic electronic
device with multiple layers of different materials. At the point of bending, the materials can be
under considerable stress. Having a material that can readily deform to this stress can partially
relieve fatigue experienced by the device and improve the overall mechanical durability fot he
device. Similarly, having elastomeric organic semiconductors on top of an elastomeric substrate
may allow for the development of an elastomeric device. Of course, these lofty claims require
further material development and device integration to prove the concept. Regardless, these new
materials really represent a new approach to thinking about organic electronic materials by
designing them with the final physical state in mind instead of just electronic properties.
150
150
I believe that the synthetic strategies developed within this thesis have the potential to allow the
development of truly flexible or stretchable electronic devices. This is enabled by relatively
simple and scaleable chemistry and the use of silicone components. The Piers-Rubinsztajn
reaction used throughout this thesis is very easy to perform and our demonstration of using it to
polymerize samples in-situ further hints at its utility. As well, the use of silicones derived from
silanes allows the use of a wide array of already commercialized starting materials.
Understanding the full scope of this chemical strategy will require only time and creativity.
All of this potential on the chemistry side is further encouraged by the preliminary findings that
silicone functionalization has very little detrimental effect on the charge transporting properties
of triarylamines. A great deal of further work will be required to make a general case and other
classes of materials will be needed as well.
11.2 Future Directions
The following paragraphs are some ideas for future projects based on the work presented here in
this thesis.
As stated above, I believe that there is a great deal of future potential in this project. This will
require new perspectives on the work and motivated researchers. There are two basic areas for
future work on this project: application of soft materials in devices and further exploration of the
chemistry.
In terms of application of these materials in devices, the key challenge will be in exploiting the
unique physical properties of these materials in devices. This obviously poses difficulties in
adapting device architectures to suite the unique processing requirements that these materials
present. Focusing on the liquid materials, the first major obstacle in application involves finding
a suitable architecture that allows for relatively thick semiconducting layers. Due to surface
tension of a liquid, it is unrealistic to utilize liquid organic semiconductors in devices which are
optimal with layer thicknesses under 1 µm. As well, it would be relatively difficult to find a way
to define a layer this thick using conventional spacers. This instantly rules out conventional
excitonic photovoltaic structures and OLEDs. Due to the intentionally low intermolecular order
151
151
found in these materials, tradition dictates that high performance organic field-effect transistors
are out of the question as well. But all is not lost. There are many potentially useful device types
that may not be as popular as the aforementioned examples, but may be more amenable to liquid
organic semiconductors.
The easiest place to start would be in devices which have already been shown to work with
liquid organic or low Tg semiconductors. Photorefractive devices had a boom in publications in
early 2000s but no commercialization or common application has been realized. Application of
our liquid organic semiconducting materials into these devices seems obvious as optimal
performance has already been achieved with amorphous, low Tg semiconductors. Typically, the
low Tg requirement was achieved by the use of plasticizers or low Tg semiconducting polymers.
Using a low Tg semiconductor could lead to a simplified cell structure. As well, a liquid organic
semiconductor has already been proven to be a viable option for these devices.1 More
background here can be found in Chapter 2. Application of our materials into photorefractive
formulations may be an immediate opportunity.
The other area which I believe may be of most interest to future graduate students is using these
materials as redox mediators for dye sensitized solar cells. A liquid triarylamine was used as a
non-volatile liquid mediator in a dye sensitized solar cell previously.2 Moreover, through
collaboration with a researcher at York university, we have already shown that silicon hybridized
triarylamines can function as efficient redox mediators.3 This example however, relies on a solid
materials in a solvent solution. Provided that any formulation issues can be solved, I believe that
superior efficiencies can be achieved using our new synthetic methodologies as a basis for
optimized materials.
Another relatively straightforward project for the liquid organic semiconductors would be
extension beyond triarylamines to other functional materials. We initially chose triarylamines as
they were simple to produce and could be studied fairly easily. But, other materials with new
functions should also be amenable to this chemistry and may open up the door to further
application.
The cross-linked systems that we demonstrated have much more potential to be applied in
conventional devices if time is taken to properly investigate them. We have already shown that
152
152
very thin layers can be produced with this system so that integration into OLEDs or organic
photovoltaics should be possible. However, the biggest unknown remaining in this project is the
effect of residual tris(pentafluorophenyl)borane (BCF) catalyst in the film itself. Because this
catalyst is highly electrophilic and electrochemically active, there is the possibility that it may
interact with the functional elements within the cross-linked films. The extent of this interaction
would need to be immediately studied before further integration is realized.
The other major avenue for the cross-linked films is the exploitation of longer chain siloxane
components to further lower the Tg of the final film. Currently, we have films with glass
transition temperatures just about room temperature. Including large sections of flexible siloxane
groups should be effective in lowering the glass transition and result in films that are elastomeric
in nature. I believe that such elastomeric films would be a great interest to the community and be
one of the first examples of a solid-state semiconductor with inherent mechanical flexibility. As
well, using this strategy with non-triarylamine based monomers should be an obvious step
forward to produce multi-functional films.
11.3 References
1. Ribierre, J.; Aoyama, T.; Kobayashi, T.; Sassa, T.; Muto, T.; Wada, T. J. Appl. Phys.
2007, 102, 033106
2. Snaith, H. J.; Zakeeruddin, S. M.; Wang, Q.; Péchy, P.; Grätzel, M. Nano Lett. 2006, 6,
2000.
3. Sepehrifard, A.; Kamino, B.A.; Bender, T.P.; Morin, S. ACS App. Mater. Int. 2012,, 4,
6211-6215.
153
153
Appendices
12.1 Additional Information for Chapter 3
12.1.1 Experimental Information
Materials. All reagents and starting materials were used as received. All solvents were
purchased from Caledon Laboratories (Ontario, Canada) and used as received except toluene
which was purified through a commercial solvent purification system prior to use. Deuterated
NMR solvents were purchased from Cambridge Isotopes. External standards were prepared by
sealing the standard in a melting point tube with a flame and placing it freely within the NMR
tube. NMR spectra were acquired on a Varian 400 NMR system with a field strength of 400
MHz. Size exclusion chromatography was performed using Waters Styragel HR0.5 and a Waters
Styragel HR1 placed in series, each having a column size of 4.6 x 300 mm. GPC was operated
with THF as the mobile phase at a rate of 0.75 mL/min. Detection was achieved by a UV-Vis
photodiode array. Fluorescence spectroscopy for the quenching measurements was performed in
a dimly lit room with a Perkin-Elmer L55 spectrometer. Mass spectroscopy for the dendritic
triarylamines was acquired on an Accu-TOF mass spectrometer (JEOL USA Inc. Peabody, MA)
with a DART-SVP ion source (Ionsense Inc., Saugus, MA) using He Gas at 300-500 °C.
Samples were dissolved in CH2Cl2 and introduced into the sampling region using glass melting-
point capillaries. Compounds 3-6a and 3-6b required volatilization using a butane torch directly
on the sample. Mass spectroscopy for samples 3-2a, 3-2b, and 3-2c was achieved using an
AB/Sciex QStar mass spectrometer with an ESI source (50:50 methanol and water). Cyclic
voltammetry was performed with a Bioanalytical Systems C3 electrochemical cell setup. The
working electrode was a 1 mm platinum disk with a platinum wire used as a counter electrode.
The reference electrode was a Ag/AgCl saturated salt solution. All electrochemistry was done in
“Spectro” grade dichloromethane from Caledon Laboratories. Decamethylferrocene was added
to the solutions as an internal reference, and all electrochemical half-wave potentials are
corrected to its published potential of -0.012 V (vs Ag/AgCl). The synthesis of 3,4-DMPhO-
BsubPc and the syntheses of compounds 3-1a to 3-1i have been previously reported in our
group.
154
154
Synthesis of 3-2a. 1,4-Phenylene diamine (1.000 g, 9.25 mmol), sodium tert-butoxide (5.332 g,
55.5 mmol), and bis-(dibenzylideneacetone)palladium (106 mg, 0.18 mmol) were added to a
round-bottom flask. This flask was sealed under an argon atmosphere. Anhydrous toluene
(50mL), 4-bromoanisole (7.611 g, 40.69 mmol), and tri-tert-butylphosphine (29.9 mg, 0.15
mmol, added as a stock solution in toluene) were added. This mixture was refluxed under an
inert atmosphere for 2 h. Upon cooling, acidic clay (10 g, montmorillonite K10) and acidic
alumina (1 g, standard basic) were added to the mixture. This slurry was filtered, washing with
toluene to yield a clear, pale yellow solution. This solution was precipitated into methanol to
yield 4.237 g of a fine pale white powder (86.3% yield). 1H NMR (400 MHz, C6D6): δ7.14 (d, J
= 9.08 Hz, integration obscured by solvent peak), 7.08 (s, 4H), 6.73 (d, J = 9.08 Hz, 8H), 3.30 (s,
12H). 13C NMR (100 MHz, C6D6): 156.34, 143.84, 142.55, 126.35, 124.17, 115.45, 53.39.
HRMS [M+] calculated 532.2356, found 532.2372.
Synthesis of 3-2b. 1,3-Phenylene diamine (1.000 g, 9.25 mmol), sodium tert-butoxide (5.332 g,
55.5 mmol), and bis-(dibenzylideneacetone)palladium (106 mg, 0.18 mmol) were added to a
round-bottom flask. This flask was sealed under an argon atmosphere. Anhydrous toluene
(50mL), 4-bromoanisole (7.611 g, 40.69 mmol), and tri-tert-butylphosphine (29.9 mg, 0.15
mmol, added as a stock solution in toluene) were added. This mixture was refluxed under an
inert atmosphere for 2 h. Upon cooling, acidic clay (10 g, montmorillonite K10) and acidic
alumina (1 g, standard basic) were added to the mixture. This slurry was filtered washing with
toluene to yield a clear, pale yellow solution. This solution was concentrated under vacuum and
precipitated into methanol. A light yellow powder was collected and dried under vacuum to
obtain 3.728 g of dry material (75.7% yield). 1H NMR (400 MHz, C6D6): δ 7.11 (d, J = 9.08 Hz,
8H), 6.73 (dd, J1 = 7.91 Hz, J2 = 2.34 Hz, 2H), 7.05 (t, J = 2.34 Hz, 1H), 7.02 (d, J = 7.92 Hz,
1H), 6.67 (d, J = 9.08 Hz, 8H), 3.28(s, 12H). 13C NMR (100 MHz, C6D6): 156.56, 150.48,
141.92, 130.30, 127.04, 115.36, 115.30, 114.71, 53.31. HRMS [M+H] calculated 533.2434,
found 533.2429.
Synthesis of 3-2c. Bis(4-methoxyphenyl)amine (3.824 g, 16.8 mmol), 4,40-dibromobiphenyl
(2.500 g, 8.0 mmol), sodium tertbutoxide (1.922 g, 20 mmol), palladium(II) acetate (72 mg, 0.3
mmol), tri-tert-butylphosphine (52 mg, 0.3 mmol, added from stock solution in anhydrous
toluene), and anhydrous toluene (20 mL) were reacted for 3 h at reflux under an inert
155
155
atmosphere. After cooling, acidic clay (2 g, montmorillonite K10) and acidic alumina (1 g,
standard basic) were added, and the mixture was filtered. The compound was precipitated into
methanol and recrystallized from EtOAc. Slightly crystalline yellow flakes were collected (4.880
g, 70%). 1H NMR (400 MHz, C6D6): δ 7.46 (d, J = 8.61 Hz, 4H), 7.17 (m, obscured by residual
solvent), 7.12 (d, J = 9.00 Hz, 8H), 6.74 (d, J = 9.00 H, 8H), 3.31 (s, 12H). 13C NMR (100 MHz,
C6D6): δ 156.43, 148.16, 141.72, 133.98, 127.56, 126.82, 122.04, 55.06.
Synthesis of N-tBOC-bis(4-bromophenyl)amine (3-4). Bis(4-bromophenyl)amine (25 g, 76.43
mmol), di-tert-butyl dicarbonate (18.32 g, 84.07 mmol), 4-dimethylaminopyridine (1.872 g,
15.29 mmol), and tetrahydrofuran (125 mL) were added to an oven-dried flask. The flask was
refluxed for 24 h and allowed to cool. Approximately 75 mL of solvent was removed by rotary
distillation, and the flask was cooled to 5 °C overnight. Large white crystals were isolated from
the mother liquor and washed lightly with cold methanol. The final pure product was dried
overnight under vacuum (26.14 g, 80% yield). 1H NMR (400 MHz, CDCl3): δ 7.43 (d, J = 8.86
Hz, 4H), 7.06 (d, J = 8.86 Hz, 4H), 1.44 (s, 12H). 13C NMR (100 MHz, CDCl3): δ 153.35,
141.93, 132.15, 128.68, 119.52, 82.16, 28.35.
Synthesis of Generation 1 Dendron (3-5a). Palladium acetate (146 mg, 0.65 mmol) and tri-tert-
butylphosphine (105.25 mg, 0.52 mmol) were added to an oven-dried flask under a flow of argon
and allowed to stir for 30 min. 4 (27.77 g, 65.01 mmol), bis(3,4-dimethylphenyl)amine (3-3)
(30.766 g, 136.54 mmol), sodium tert-butoxide (16.66 g, 173.36 mmol), and 90 mL of toluene
were then added to the flask. The solution was refluxed for 2 h and allowed to cool. When the
solution was at room temperature, an additional 100 mL of toluene was added, and the solution
was treated with 5 g of basic alumina and 5 g of montmorillonite K10 clay. The solution was
filtered, and the yellow mother liquor was collected and concentrated under vacuum. The now
concentrated and viscous solution was precipitated into 50 mL of methanol and allowed to stir.
The collected solid was dried and placed into a vessel with 10 mL of tetralin (1,2,3,4-
tetrahydronaphthalene) and heated at 200 °C under an argon atmosphere overnight. The still
yellow solution was allowed to cool and precipitated into 50 mL of methanol to yield a white
solid (40.721 g, 78% yield). Mass Spectroscopy [M+H]: 616.3690. Expected [M+H]: 616.3691.
Synthesis of Generation 1 Dendrimer (3-5b). Bis(dibenzylideneacetone) palladium (14 mg,
0.024 mmol) and tri-tertbutylphosphine (4 mg, 0.02 mmol, added as a stock solution in toluene)
156
156
were added to an oven-dried flask under a flow of argon and allowed to stir for 30 min.
Compound 3-5a (300 mg, 0.49 mmol), 4-bromotoluene (13 mg, 0.73 mmol), sodium tertbutoxide
(94 mg, 1.0 mmol), and 2 mL of anhydrous toluene were added, and the solution was refluxed
overnight. Upon completion, the solution was allowed to cool and then treated with basic
alumina (0.25 g) andmontmorillonite K10 clay (0.25 g). The solids were filtered, washing with
additional toluene, and reduced to a viscous liquor. This liquor was precipitated by dropwise
addition into 50 mL of stirring methanol. A white, fluffy powder was collected (305 mg, 89%
yield). The compound was characterized by NMR, mass spectroscopy, and gel permeation
chromatography. 1H NMR (400 MHz, CDCl3): δ 7.15-7.09 (m, 14H), 7.03 (dd, J1 = 8.19 Hz, J2
= 2.14 Hz, 4H), 6.92 (d, J = 7.99 Hz, 4H), 6.87 (d, J = 8.19 Hz, 2H), 2.07 (s, 3H), 2.00 (s, 12H),
1.91 (s, 12H). Mass Spectroscopy [M+H]: 706.4143. Expected [M+H]: 706.4161.
Synthesis of Generation 2 Dendron (3-6a). Palladium acetate (217 mg, 0.97 mmol) and tri-tert-
butylphosphine (156 mg, 0.77 mmol) were added to an oven-dried flask under a flow of argon
and allowed to stir for 30 min. 3-5a (20 g, 32.47 mmol), 4 (6.866 g, 16.08 mmol), sodium tert-
butoxide (4.057 g, 42.22 mmol), and 100mL of toluene were then added to the flask. The
solution was refluxed for 18 h and allowed to cool. When the solution was at room temperature,
an additional 150 mL of toluene was added, and the solution was treated with 5 g of basic
alumina and 5 g of montmorillonite K10 clay. The solution was filtered, and the yellow mother
liquor was collected and concentrated under vacuum. The now concentrated and viscous solution
was precipitated into 50 mL of methanol and allowed to stir. The collected solid was dried and
placed into a vessel with 10 mL of tetralin (1,2,3,4-tetrahydronaphthalene) and heated at 200 °C
under an argon atmosphere overnight. The still yellow solution was allowed to cool and
precipitated into 50 mL of methanol to yield a white solid (22.455 g, 91% yield). Mass
Spectroscopy [M+H]: 1396.8. Expected [M+H]: 1396.8.
Synthesis of Generation 2 Dendrimer (3-6b). Bis(dibenzylideneacetone) palladium (6 mg, 0.01
mmol) and tri-tert-butylphosphine (1.74 mg, 0.009 mmol, added as a stock solution in toluene)
were added to an oven-dried flask under a flow of argon and allowed to stir for 30 min.
Compound 3-6a (300 mg, 0.215 mmol), 4-bromotoluene (55 mg, 0.322 mmol), sodium tert-
butoxide (41 mg, 0.430 mmol), and 2 mL of anhydrous toluene were added, and the solution was
refluxed overnight. Upon completion, the solution was allowed to cool and then treated with
157
157
basic alumina (0.25 g) and montmorillonite K10 clay (0.25 g). The solids were filtered, washing
with additional toluene, and reduced to a viscous liquor. This liquor was precipitated by adding
dropwise into 50 mL of stirring methanol. A yellow, fluffy powder was collected (295 mg, 92%
yield). Compound was characterized by NMR, mass spectroscopy, and gel permeation
chromatography. 1H NMR (400 MHz, C6D6 �): δ 7.14 6.86 (m, 52), 2.09 (s, 3H), 2.00 (s, 24H),
1.90 (s, 24H). 13C NMR (100 MHz, C6D6): δ 147.11, 144.23, 143.57, 143.55, 143.14, 137.94,
132.30, 131.19, 131.16, 131.00, 130.58, 128.27, 126.47, 125.45, 125.39, 125.01, 124.85, 122.80,
21.12, 20.14, 19.42. Mass Spectroscopy [M+H]: 1486.8. Expected [M+H]: 1486.8.
12.1.2 Supplemental Information of Merit
NN
NH2
NH2
Pd(dba)2P(t-butyl)3Na(t-butoxide)
Toluene
OMe
Br
N
NH2
Pd(dba)2P(t-butyl)3Na(t-butoxide)
Toluene
OMe
Br
MeO OMe
OMeMeO
NH2
N
OMe
MeO OMe
OMe
Br BrNH
OMe
MeO Pd(OAc)2P(t-butyl)3Na(t-butoxide)
TolueneN N
MeO
MeO OMe
OMe
2a
2b
2c
Figure S3-1: Synthetic scheme for the synthesis of two nitrogen centered triarylamines (3-2a-
c)
3.0 Electrochemistry of New Compound
158
158
-0.4 -0.2 0 0.2 0.4 0.6 0.8 1 1.2 1.4
Cu
rre
nt
(µA
)
Voltage (V)
2a
2c
2b
2b to1100 mV
Figure S3-2: Cyclic voltammetry of compounds 3-2a-c in dichloromethane with 0.1 M
tetrabutylammonium perchlorate scanned at a rate of 50 mV/s.
-0.4 0.1 0.6 1.1 1.6
Voltage (V)
5b
5b to 1400 mV
6b
6b to 1400 mV
Figure S3-3: Cyclic voltammetry of compounds 3-5b and 3-6b in dichloromethane with 0.1 M
tetrabutylammonium perchlorate scanned at a rate of 50 mV/s.
159
159
Table S3-1: Collects the calculated molecular volumes and radii from molecular mechanics calculations and the square of the residual values from the Stern Volmer plots.
Compound
Results from MM calculations Quality of Stern
Volmer Fit
Molecular Volume
(Å3) Spherical Radii (Å) R2
3-1a 369.96 4.453369398 0.9381
3-1b 379.56 4.491560731 0.9967
3-1c 370.53 4.455655337 0.9946
3-1d 361.5 4.419161746 0.9927
3-1e 424.56 4.662478281 0.997784
3-1f 365.28 4.434511256 0.994205
3-1g 357.09 4.401118138 0.992294
3-1h 357.06 4.400994885 0.97302
3-1i 294 4.124958406 -
3-2a 569.62 569.62 0.9893
3-2b 569.61 569.61 0.9976
3-2c 653.47 653.47 0.9999
3-5b 804.95 653.47 0.9699
3-6b 1673.57 653.47 0.9973
160
160
12.2 Additional Information for Chapter 4
12.2.1 Experimental Information
12.2.1.1 General Procedures
All silicon containing materials were purchased from Gelest Inc. and used without further
purification. Palladium catalysts were purchased from Strem Chemicals Inc. and stored in an
inert atmosphere glovebox. Reagent grade solvents were purchased from Caledon Laboratories.
Toluene and DMF were dried and degassed using a solvent purification system prior to use. All
other solvents were used as received. Sodium tert-butoxide was stored either in an inert
atmosphere glovebox or in a desiccator. All Buchwald-Hartwig aminations were performed in a
glove box with an argon atmosphere. Other reactions were preformed under an argon atmosphere
using standard procedures. Reactions were monitored by reverse phase HPLC (Waters PAH C18
5 µm, acetonitrile mobile phase 1.2 mL/min, photodiode array detector) or by low molecular
weight GPC (Waters Styragel HR-1 and Styragel HR-2 in series, eluting with THF at 0.75
mL/min). All NMR spectra were collected on a Varian Mercury 400 spectrometer. Chemical
shifts are reported in parts per million referenced to either tetramethylsilane (TMS) internal
standard or relative to residual C-H solvent peaks. Coupling constants (J) are reported in Hz.
Mass spectroscopy was taken with an AB/Sciex QStar mass spectrometer. Samples were
introduced with an ESI source in solution (50:50 methanol and water) via an HPLC pump.
Cyclic voltammetry was performed with a Bioanalytical Systems C3 electrochemical cell setup.
The working electrode was a 1 mm platinum disc with a platinum wire used as a counter
electrode. The reference electrode was a Ag/AgCl saturated salt solution. All electrochemistry
was done in spectro grade dichloromethane from Caledon Laboratories. Decamethylferrocene
was added to the solutions as an internal reference. All electrochemical half wave potentials are
corrected to the decamethylferrocene half wave potential of −0.012 V (vs. Ag/AgCl).
Differential scanning calorimetry was performed with a TA instruments DSC2920 equipped with
a refrigerated cooling system. All samples were heated from 30 °C to 200 °C or 110 °C at 10
°C/min with a ±0.5 °C modulation every 30 s. The samples were rapidly cooled to −50 °C then
heated again to 200 °C or 110 °C at 10 °C/min with the same temperature modulation.
161
161
12.2.1.2 Synthesis
bis(3,4-dimethylphenyl)amine (4-2): 3,4-Dimethylaniline (50.3 g, 0.415 mol) was added to a
round bottom flask was heated to 60 °C under argon. After the aniline was completely melted,
anhydrous calcium chloride (12.0 g, 0.108 mol), aluminum chloride (15.4 g, 0.115 mol), and 30
mL of tetrahydronaphthalene (tetralin) were added. The flask was heated to 220 °C for 18 h. The
flask was allowed to cool and diluted with 60 mL of toluene. The organic phase was added to
~200 mL of ice water and allowed to separate. The organic phase was washed with 3×75 mL of
5% aqueous hydrochloric acid solution, 75 mL of 5% aqueous sodium bicarbonate and 100 mL
of an aqueous saturated brine solution. The organic phase was dried over MgSO4 and distilled
under vacuum to remove remaining solvent. After the majority of the tetralin had been removed
the organic phase was allowed to cool to ~60 °C, at this point 40 mL of methanol was quickly
added and the solution was stored at 3-5 °C overnight. Slightly red crystals were collected and
washed with cold methanol and dried under vacuum. 21.52 g was collected (46% Yield). 1H
NMR (400 MHz, CDCl3): δ 7.00 (d, J=7.95 Hz, 2 H), 6.83 (s, 2 H), 6.79 (d, J=7.95 Hz, 2 H),
5.28 (s, 1 H), 2.21 (s, 6 H), 2.19 (s, 6 H). 13C NMR (100 MHz, CDCl3): δ 141.80, 137.30,
130.51, 129.07, 119.67, 115.43, 20.19, 19.15.
p-triisopropylsiloxy-bromobenzene (4-3a): Triisopropylchlorosilane (25.0 g, 0.1297 mol), 4-
bromophenol (21.3 g, 0.1232 mol), imidazole (16.8 g, 0.2464 mol), and 125 mL of N,N-
dimethylformamide were stirred at room temperature overnight. The solution was added to a
separatory funnel where 65 mL of water was added. The product was extracted with hexanes
(3x100mL). The hexanes phase was dried over magnesium sulphate and removed under vacuum
to yield a clear oil. 40.57 g was recovered (100% yield). Trace amounts of DMF can be detected
in the 1 H NMR (resonances not indicated). 1H NMR (400 MHz, CDCl3): δ 7.31 (d, J= 8.848 Hz,
2 H), 6.77 (d, J=8.848 Hz, 2 H), 1.25 (s, 3 H), 1.1 (d, J=7.16 Hz, 18 H). 13C NMR (100 MHz,
CDCl3): δ 155.51, 132.47, 121.92, 113.44, 18.11, 12.86. Theoretical MS (ESI) of C15H25BrOSi
[M]: 328.1. Mass found: 328.1
p-tertbutyldimethylsiloxy-bromobenzene (4-3b): The same general procedure for 4-3a was
repeated, using tertbutyldimthylsilyl chloride. The product was isolated as a clear oil in
quantitative yield. The product was used without further purification. Trace amounts of DMF can
be detected in the 1H NMR (resonances not indicated). 1H NMR (400 MHz, CDCl3): δ7.33 (d,
162
162
J=8.6 Hz, 2 H), 6.73 (d, J=8.59 Hz, 2 H), 0.99 (s, 9 H), 0.19 (s, 6 H). 13C NMR (100 MHz,
CDCl3): δ 154.66, 132.15, 121.73, 113.50, 25.52, 18.02, - 4.61. Theoretical MS (ESI) of
C12H19BrOSi [M]: 286.0. Mass found: 286.0
p-terthexylsiloxy-bromobenzene (4-3c): The same general procedure for 4-3a was repeated,
using tert-hexyl-di-methylsilyl chloride. The product was isolated as a slightly yellow clear oil in
quantitative yield. The product was used without further purification. 1H NMR (400 MHz,
CDCl3): δ7.32 (d, J=8.59 Hz, 2 H), 6.71 (d, J= 8.59 Hz, 2 H), 1.73 (m, J=7.03 Hz, 1 H), 0.94 (d,
J= 7.03 Hz), 0.94 (s, integration with previous peak comes 12 H), 0.22 (s, 6 H). 13C NMR (100
MHz, C6D6): δ 155.27, 132.96, 122.55, 114.30, 34.85, 25.64, 20.72, 19.22, -2.01. Theoretical
MS (ESI) of C14H23OBrSi [M]: 314.1. Mass found: 314.1
p-diphenyltertbutylsiloxy-bromobenzene (4-3d): The same general procedure for 4-3a was
repeated, using di-phenyl-tert-butylsilyl chloride. The product was isolated as a white soft
crystalline solid in quantitative yield. The product was used without further purification. 1H
NMR (400 MHz, CDCl3): δ7.74-7.67 (m, 4 H), 7.48-7.36 (m, 6 H), 7.19 (d, J=9.18 Hz, 2 H),
6.64 (d, 9.2 Hz, 2 H), 1.1 (s, 9 H). 13C NMR (100 MHz, CDCl3): δ 154.71, 135.43, 132.39,
132.05, 130.02, 127.83, 121.45, 113.32, 26.42, 19.40. Theoretical MS (ESI) of C22H23BrOSi
[M]: 410.1 Mass found: 410.1
4-4a: Palladium acetate (102 mg, 0.45 mmol) and tri-tertbutylphosphine (73 mg, 0.36 mmol, in
0.01 g/mL stock solution in anhydrous toluene) were added to a round bottom flask and stirred at
room temperature for 30 min. To this flask, p-triisopropylsiloxy-bromobenzene (4-3a) (2.98 g,
9.048 mmol), bis(3,4-dimethylphenyl)amine (2) (2.24 g, 10 mmol), and sodium tert-butoxide
(0.961 g, 10 mmol) were added and the solution was refluxed for 4 h. The solution was taken out
of the glove box where it was treated with 10 g of Montmorillonite clay (Montmorillonite K10
from Sigma) for 15 min and subsequently filtered to remove solids leaving a slightly yellow
solution which was washed with additional toluene. Solvent was removed under vacuum leaving
an off white fluffy solid. This was dispersed in 100 mL of methanol and allowed to stir in the
dark overnight. The methanol slurry was filtered yielding a pure white solid. 3.60 g was
recovered (84% yield). 1H NMR (400 MHz, CDCl3): δ 6.99–6.90 (m, 4H), 6.84–7.70 (6H), 2.19
(s, 6 H), 2.14 (s, 6H), 1.24 (m, 3H), 1.10 (d, J= 7.1 Hz, 18H). 13C NMR (100 MHz, CDCl3): δ
163
163
151.74, 146.28, 141.65, 137.13, 130.07, 129.82, 126.32, 124.41, 120.60, 120.49, 19.89, 19.02,
17.91, 12.62. Theoretical MS (ESI) of C31H44NOSi [M+H]: 474.3. Mass found: 474.3.
4-4b: Same procedure as 4-4a except 4-3b was used as the aryl bromide. The completed reaction
was purified by column chromatography on silica eluting with cyclohexane and toluene. The
product was isolated as a white crystalline solid in a 74% yield. 1H NMR (400 MHz, CDCl3): δ
7.15 (d), 7.11 (d, J=2.3 Hz, 2H), 7.04 (dd, J1=8.0 Hz, J2=2.3 Hz, 2H), 6.93 (d, J=8.0 Hz, 2H),
6.79 (d, J=8.96 Hz, 2H), 2.01 (s, 6H), 1.92 (s, 6H), 0.99 (s, 9H), 0.11 (s, 6H). 13C NMR (100
MHz, C6D6): δ 151.82, 147.50, 143.32, 137.84, 131.10, 130.75, 126.48, 125.93, 122.25, 121.27,
26.22, 20.16, 19.39, 12.75, -4.01. Theoretical MS (ESI) of C30H42NOSi [M+H]: 432.3 found:
432.3.
4-4c: Same procedure as 4-4a except 4-3c was used as an aryl bromide. The completed reaction
was purified by precipitating into 100 mL of methanol to yield a white crystalline solid. The
product was isolated as white crystalline powder in an 85% yield. 1H NMR (400 MHz, C6D6): δ
7.16, (d, J=8.77 Hz, integration obscured by solvent peak), 7.11 (d, J=2.3 Hz, 2H), 7.04 (dd,
J1=8.19 Hz, J2=2.3 Hz, 2H), 6.93 (d, J= 8.19 Hz, 2H), 6.78 (d, J=8.77 Hz, 2H), 2.01 (s, 6H),
1.92 (s, 6H), 1.69 (m, J=6.82 Hz, 1H), 0.96 (d, J=6.82 Hz), 0.94 (s, integration with previous
peak is 12H), 0.16 (s, 6H,). 13C NMR (100 MHz, C6D6): δ 151.66, 147.51, 143.29, 137.814,
131.10, 130.73, 126.52, 125.91, 122.23, 121.38, 34.90, 25.64, 20.75, 20.17, 19.39, 19.16, -2.02.
Theoretical MS (ESI) of C30H41NOSi [M+H]: 460.3 found: 460.3.
4-4d: Same procedure as 4-4a except 4-3d was used as an aryl bromide. The completed reaction
was purified by column chromatography on silica eluting with cyclohexane and toluene. The
product was isolated as light orange glass in 64% yield. 1H NMR (400 MHz, CDCl3): δ 7.82–
7.77 (m, 4H), 7.16–7.14 (m), 6.99 (d, J= 2.1 Hz, 2H), 6.93 (dd, J1=8.10 Hz, J2=2.53 Hz), 6.92
(d, J= 8.96 Hz, this and previous peak integrate to 4H), 6.86 (d, J=8.19 Hz, 2H), 6.78 (d, J=8.96
Hz, 2H), 1.99 (s, 6H), 1.89, (s, 6H), 1.18 (s, 9H). 13C NMR (100 MHz, C6D6): δ 151.75, 147.36,
141.16, 137.70, 136.33, 133.87, 131.01, 130.64, 130.49, 128.46, 126.08, 125.94, 122.26, 120.78,
27.15, 20.13, 20.04, 19.38. Theoretical MS (ESI) of C38H42NOSi [M+H]: 556.3 found: 556.3.
4-5: Palladium acetate (46 mg, 0.2 mmol) and tri-tertbutylphosphine (33 mg, 0.16 mmol, in 0.01
g/mL stock solution in anhydrous toluene) were added to a round bottom flask and stirred at
164
164
room temperature for 30 min. To this flask, p-triisopropylsiloxy-bromobenzene (4-3a) (2.98 g,
9.048 mmol), 3,4-dimethylaniline (4-1) (0.5 g, 4 mmol), and sodium tert-butoxide (0.990 g, 10
mmol) were added and the solution was refluxed for 4 h. The reacted solution was filtered
washing with toluene and the resulting oil was purified by column chromatography over silica
gel eluting with cyclohexane. The compound was isolated as a yellow oil. 1.15 g was collected
(45% yield). 1H NMR (400 MHz, CDCl3): δ 6.97–6.86 (5 H), 6.78–6.69 (6H), 2.18 (s, 3H), (2.12
(s, 3H), 1.23 (m, 6H), 1.09 (d, J=7.08 Hz, 36H). 13C NMR (100 MHz, CDCl3): δ 151.33, 146.59,
141.85, 137.05, 130.03, 129.37, 125.38, 123.75, 120.37, 119.89, 19.88, 18.87, 17.92, 12.63.
Theoretical MS (ESI) of C38H60NO2Si2 [M+H+]: 618.4. Mass found: 618.4.
4-6: Palladium acetate (46 mg, 0.2 mmol) and tri-tertbutylphosphine (33 mg, 0.16 mmol, in 0.01
g/mL stock solution in anhydrous toluene) were added to a round bottom flask and stirred at
room temperature for 30 min. To this flask, p-triisopropylsiloxy-bromobenzene (4-3a) (2.98 g,
9.048 mmol), lithium amide (0.064 g, 2.8 mmol), and sodium tert-butoxide (0.990 g, 9.048
mmol) was added. The solution was refluxed for 16 h. The reacted solution was filtered to
washing with additional toluene. The filtrate was purified by column chromatography over silica
gel eluting with cyclohexane. This yielded a yellow clear waxy solid. 0.925 g of product was
recovered (43.5% yield). 1H NMR (400 MHz, CDCl3): δ 6.86 (d, J=4.56 Hz, 6 H) 6.73 (d, J=4.56
Hz, 6 H), 1.23 (m, 9 H), 1.09 (d, J=7.18 Hz, 54 H). 13C NMR (100 MHz, CDCl3): δ 150.95,
142.11, 124.55, 120.29, 17.93, 12.63. Theoretical MS (ESI) of C45H76NO3Si3 [M+H]: 762.5.
Mass found: 762.5.
4-7: Bis(dibenylideneacetone)palladium(0) (71 mg, 0.124 mmol) and tri-tert-butylphosphine (33
mg, 0.16 mmol, in 0.01 g/mL stock solution in anhydrous toluene) were added to a round bottom
flask and stirred at room temperature for 30 min. To this solution, 1,3-phenylenediamine (671
mg, 6.21 mmol), p-triisopropylsiloxy-bromobenzene (4-3a) (9 g, 27.3mmol), and sodium tert-
butoxide (2.98 g, 31 mmol) were added and the solution was refluxed overnight. The solution
was then filtered eluting with additional toluene. The filtrate was purified by column
chromatography over silica gel eluting with cyclohexane then a gradation to 3:1
cyclohexane:toluene. The product was isolated as a slightly yellow perfectly clear glass. 3.119 g
of product was obtained (46% yield). 1H NMR (400 MHz, C6D6): δ7.13 (t, J=2.14 Hz, 1 H), 7.07
(d, J= 8.96 Hz, 8 H), 6.99 (t, J=8.18 Hz, 1 H), 6.77 (d, 8.96 Hz), 6.75 (dd, J1=8.18 Hz, J2=2.14
165
165
Hz, integration with previous peak is 10 H), 1.14 (m), 1.10 (d, J=5.65 Hz, integration over both
peaks is 84 H). 13C NMR (100 MHz, C6D6): δ152.48, 150.33, 142.39, 130.40, 126.64, 121.19,
116.48, 115.91, 18.51, 13.33. Theoretical MS (ESI) of C66H105N2O4Si4 [M+H]: 1101.7. Mass
found: 1101.7.
4-8a: Bis(dibenylideneacetone)palladium(0) (212 mg, 0.37 mmol) and tri-tert-butylphosphine
(60 mg, 0.296 mmol, in 0.01 g/mL stock solution in anhydrous toluene) were added to a round
bottom flask and stirred at room temperature for 30 min. To this solution, 1,4- phenylenediamine
(2 g, 18.5 mmol), p-triisopropylsiloxy- bromobenzene (4-3a) (26.80 g, 81.4 mmol), and sodium
tert-butoxide (8.88 g, 92.5 mmol) were added and refluxed overnight. The solution was then
filtered washing with additional toluene. This filtrate was purified by column chromatography
over silica gel eluting with cyclohexane and a gradation to 1:1 cyclohexane and toluene. The
purity of this compound was assessed by low molecular weight GPC and TLC analysis. The
product was isolated as a white crystalline solid. 14.460 g of product was obtained (71% yield).
A crystal suitable for X-ray diffraction was grown by taking up 50 mg of compound in 5 mL of
toluene, this vial was placed in a sealed container with 100 mL of acetonitrile. 1H NMR (400
MHz, C6D6): δ7.10 (d, J=8.96 Hz, 8 H), 7.06 (s, 4 H), 6.80 (d, J=8.96 Hz, 8 H), 1.14 (m), 1.11
(d, J=6.04 Hz). 13C NMR (100 MHz, C6D6): δ 152.19, 143.82, 142.84, 126.06, 124.60, 121.18,
18.51, 13.34. Theoretical MS (ESI) of C66H104N2O4Si4 [M]: 1100.7. Mass found: 1100.7.
4-8b: Bis(dibenylideneacetone)palladium (0) (38 mg, 0.066 mmol) and tri-tert-butylphosphine
(11 mg, 0.053 mmol, in 0.01 g/mL stock solution in anhydrous toluene) were added to a round
bottom flask and stirred at room temperature for 30 min. To this solution, 1,4-phenylenediamine
(90 mg, 0.83 mmol), p-diphenyltertbutylsiloxybromobenzene (4-3d) (2 g, 4.98 mmol), and
sodium tertbutoxide 400 mg, 4.16 mmol) were added and was refluxed overnight. The solution
was filtered washing with and the filtrate was purified by column chromatography over silica gel
eluting with 5:1 cyclohexane:toluene and then a gradation to 1:1 cyclohexane:toluene. 0.881 g of
small white needles was obtained (71% yield). 1H NMR (400 MHz, CDCl3): δ 7.86–7.79 (m, 16
H), 7.19–7.14 (m, integration obscured by solvent), 6.84–6.71 (m, 20 H), 1.18 (s, 36 H). 13C
NMR (100 MHz, C6D6): δ 151.14, 142.86, 142.25, 135.80, 133.32, 130.02, 127.99, 125.26,
123.95, 120.45, 26.62, 19.51. Theoretical MS (ESI) of C96H96N2O4Si4 [M]: 1428.6. Mass found:
1428.6
166
166
4-9: Bis(dibenylideneacetone)palladium (0) (125 mg, 0.217 mmol) and tri-tert-butylphosphine
(35 mg, 0.174 mmol, in 0.01 g/mL stock solution in anhydrous toluene) were added to a round
bottom flask and stirred at room temperature for 30 min. To this solution, benzidine (1.000 g,
5.428 mmol), p-triisopropylsiloxy-bromobenzene (4-3a) (10.726 g, 32.57 mmol), and sodium
tert-butoxide (3.129 g, 32.57 mmol) were added with 30 mL of toluene to wash down the solid.
The reaction was refluxed for 35 h and allowed to cool. The solution was treated with 10 g of
Montmorillonite clay (Montmorillonite K10 from Sigma) and filtered to remove solid by
washing with toluene. The product was purified by column chromatography over silica gel
eluting with 10:1 cyclohexane:toluene and then a gradation to 4:1 cyclohexane:toluene. 5.280 g
of white hard solid was obtained (83% yield). 1H NMR (400 MHz, CDCl3): δ7.42 (d, J=8.57 Hz,
4 H), 7.17 (d, J=8.77 Hz), 7.08 (d, J=8.77 Hz, 8 H), 6.83 (d, J=8.57 Hz, 4 H), 1.15 (m) 1.11 (d,
J=6.04 Hz). 13C NMR (100 MHz, C6D6): δ 152.64, 148.35, 142.45, 134.54, 127.89, 126.78,
123.02, 121.27, 18.51, 13.36. Theoretical MS (ESI) of C72H108N2O4Si4 [M]: 1176.7. Mass found:
1176.7.
4-10: Bis(dibenylideneacetone)palladium (0) (92 mg, 0.16 mmol) and tri-tert-butylphosphine
(0.026 g, 0.128 mmol, in 0.01 g/mL stock solution in anhydrous toluene) were added to a round
bottom flask and stirred at room temperature for 30 min. To this solution, 4,4`-dibromobiphenyl
(5 g, 16 mmol), 3,4-dimethylaniline (4.078 g, 33.6 mmol), and sodium tert-butoxide (4.620 g, 48
mmol) were added with 25 mL of toluene to wash down the solid. The reaction was refluxed for
3 h. The resulting solution was treated with 10 g of montmorillonite clay (Montmorillonite K10
from Sigma) and filtered to remove solids by washing with toluene. The toluene phase was
washed 3 times with 100 mL of a 10% hydrochloric acid solution, dilute sodium carbonate and
finally dried over magnesium sulfate. The organic phase was reduced yielding a yellow powder
that was used as is. 1.136 g obtained (18% Yield). The product was used as prepared without
further purification. Theoretical HRMS for C28H28N2 [M+H] 393.2, found 393.2.
4-11: Palladium (II) acetate (6 mg, 0.0254 mmol) and tri-tertbutylphosphine (4 mg, 0.0203
mmol, in 0.01 g/mL stock solution in anhydrous toluene) were added to a round bottom flask and
stirred at room temperature for 30 min. To this solution, 10 (0.5 g, 1.27 mmol), p-
triisopropylsiloxybromobenzene (4-3a) (0.923 g, 2.802 mmol) and sodium tertbutoxide (0.305 g,
3.175 mmol) were added and the solution was refluxed for 48 h. The mixture was filtered
167
167
washing with toluene. The filtrate was purified using column chromatography over silica gel
eluting with 5:1 cyclohexane:toluene. The product was isolated as a yellow glass. 0.743 g of
material was obtained (66% yield). 1H NMR (400 MHz, CDCl3): δ 7.42 (d, J=8.77 Hz, 4 H),
7.23 (d, J=8.77 Hz, 4 H), 7.11 (d, J=8.96), 7.09 (d, J=2.34 Hz), 7.03 (dd, J1=8.19 Hz, J2=2.34 Hz,
2 H), 6.83 (d, J= 8.19 Hz, 2 H), 6.84 (d, J=8.96 Hz, 4 H), 2.02 (s, 6 H), 1.93 (s, 6 H), 1.15 (m),
1.11 (d, 5.85 Hz). 13C NMR (100 MHz, C6D6): δ 152.76, 148.27, 146.87, 142.44, 138.00, 134.70,
131.46, 131.21, 127.95, 127.20, 126.52, 123.38, 122.88, 121.28, 20.15, 19.44, 18.50, 13.34.
Theoretical MS (ESI) of C58H76N2O2Si2 [M]: 888.5. Mass found: 888.5
12.2.1.3 Hydrolytic Stability Testing
A 0.02 M solution of arylamine in 4.75 mL of 1,4-dioxane and 0.25 mL of a 1 M HCl or 10 M
NaOH aqueous solution was prepared. For an internal standard, 4,4`-dibromobiphenyl was
utilized. The solutions were stirred in the dark monitoring the decomposition by HPLC analysis.
Decomposition was fitted to a first order exponential decay and the half-life was extracted from
this curve. Further details are included in the supporting information.
168
168
12.3 Additional Information for Chapter 5
12.3.1 Experimental Information
Materials: Toluene was purified using a PureSolv solvent purification system just prior to use.
Tris(pentafluorophenyl)borane was obtained from the Sigma-Aldrich and used without further
purification. Pentamethyldisiloxane was obtained from Gelest Inc. and was used without further
purification. Deuterated benzene (C6D6) was purchased from Cambridge Isotopes and used
without further purification. Reactions were monitored by reverse phase HPLC (Waters PAH
C18 5µm, acetonitrile mobile phase 1.2 mL/min), a photo diode array (200nm-500nm) was used
for detection. All NMR spectra were collected on a Varian Mercury 400 spectrometer in C6D6.
Chemical shifts are reported in parts per million referenced relative to residual C-H solvent
peaks. Coupling constants (J) are reported in Hz. High resolution mass spectroscopy was taken
with an AB/Sciex QStar mass spectrometer. Samples were introduced with an ESI source in
solution (50:50 methanol and water) via an HPLC pump. Cyclic voltammetry was performed
with a Bioanalytical Systems C3 electrochemical cell setup. The working electrode was a 1mm
platinum disc with a platinum wire used as a counter electrode. The reference electrode was
Ag/AgCl2 saturated salt solution. All electrochemistry was done in ‘Spectro’ grade
dichloromethane from Caledon Laboratories. Decamethylferrocene was added to the solutions as
an internal reference. All DSC half wave potentials are corrected to the decamethylferrocene half
wave potential of -0.012 V (vs. Ag/AgCl). Differential scanning calorimetry was preformed with
a TA instruments Q2000 with a refrigerated cooling system. Tests were performed under a
blanket of nitrogen. Triarylamines 5-1a-c were synthesized as previously reported (Bender, T.P.;
Graham, J.F.; Duff, J.M.; Chem. Mater. 2001, 13, 4105.)
Compound 5-2a. In a round bottom flask, tris(pentafluorophenyl)borane (15 mg, 0.029 mmol, 1
mol%) was dissolved in toluene (10 mL) to which the arylamine 5-1a (1.0 g, 3.21 mmol) was
added. To this pentamethyldisiloxane (1.428 g, 9.63 mmol) was slowly added drop wise.
CAUTION under these reaction conditions, methane gas is vigorously generated in solution and
expelled by bubbling. A strong exotherm has also been observed. These considerations should be
taken into account when performing or scaling up this chemistry. Solutions were warm to the
touch after reaction. After bubbling ceased, the solutions were allow to stir for 20 minutes. At
169
169
this point 0.5 g of basic standard alumina was added to the reaction and allowed to stir for an
additional 20 minutes. The solution was filtered. Solvent and excess silane were removed by
rotary evaporation over several hours. 1.329g of product was collected (2.87 mmol, 95%). 1H
NMR (400 MHz, C6D6): δ 7.16 (d, J = 8.96 Hz, integration obscured by residual solvent peak),
7.09 (d, J = 2.14 Hz, 2H), 7.03 (dd, J1 = 7.99 Hz, J2 = 2.14 Hz, 2H), 6.94 (d, J = 8.96 Hz), 6.92
(d, J = 8.01 Hz, integration over this and last peak is 4H), 2.02 (s, 6H), 1.92 (s, 6H), 0.21 (s, 6H),
0.11 (s, 9H) 13C NMR (100 MHz, C6D6): 150.92, 147.48, 143.62, 137.82, 131.10, 130.76,
126.39, 125.98, 122.31, 121.22, 20.15, 19.39, 2.16, 0.21. Theoretical HRMS for C33H57NO6Si6
[M+H] 732.2874 found 732.2876.
Compound 5-2b: Same general procedure as for compound 5-2a using: arylamine 5-1b (1g,
3.00 mmol), tris(pentafluorophenyl)borane (15 mg, 0.029 mmol, 1 mol%),
pentamethyldisiloxane (2.670 g, 18 mmol). 1.644 g of product was collected (2.75 mmol, 92%). 1H NMR (400 MHz, C6D6): δ 7.10 (d, J= 8.96 Hz, 4H), 7.04 (d, J= 2.14 Hz, 1H), 6.97 (dd, J1
=8.19 Hz, J2 = 2.14 Hz, 1H), 6.92 (d, J= 8.96 Hz), 6.90 (d, J= 8.19 Hz, integration over this and
last peak is 5H), 2.02 (s, 3H), 1.92 (s, 3H), 0.22 (s, 12H), 0.11 (s, 18H). 13C NMR (100 MHz,
C6D6): 150.81, 147.47, 143.60, 137.79, 131.08, 130.56, 126.11, 125.56, 121.89, 121.21, 20.15,
19.39, 2.16, 0.19. Theoretical HRMS for C30H47NO4Si4 [M+H] 598.2654 found 598.2650.
Compound 5-2c: Same general procedure as for compound 5-2a using: arylamine 5-1c (0.500 g,
1.49 mmol), tris(pentafluorophenyl)borane (8 mg, 0.015 mmol, 1 mol%), pentamethyldisiloxane
(1.990 g, 13 mmol). 1.047 g of product was collected (1.43 mmol, 96%). 1H NMR (400 MHz,
C6D6): δ 7.04 (d, J= 8.96 Hz, 6H), 6.90 (d, J= 8.96 Hz, 6H), 0.22 (s, 18H), 0.11 (s, 27H). 13C
NMR (100 MHz, C6D6): 150.71, 143.65, 125.78, 121.20, 2.15, 0.18. Theoretical HRMS for
C27H37NO2Si2 [M+H] 464.2435 found 464.2425.
12.4 Additional Information for Chapter 6
12.4.1 Experimental Information
Safety note: For reactions involving Piers−Rubinsztajn chemistry (coupling of silanes using
tris(pentaf luorophenyl)borane), the reaction can proceed extremely rapidly, evolving flammable
gases with a noticeable exotherm. In our opinion, care should be exercised in scaling this
170
170
chemistry. The caref ul dropwise addition of silane(s) at a moderate rate is recommended, and if
no reaction is detected after several minutes, the addition of silane should be halted.
General Piers−Rubinsztajn Procedure (General P−R procedure).
The aryl-methoxy-functionalized substrate, tris-(pentafluorophenyl)borane, and toluene were
added to a generously sized round-bottom flask with a magnetic stirrer under atmospheric
conditions. The flask should be at least four times the volume of the reagents to prevent any
material from spilling out upon reaction. To maximize the reaction yield, the P−R reaction
should be done at anhydrous conditions using predried reagents and solvent. Silane was added
dropwise to this stirring solution, taking care to control the rate of methane evolving. Upon
completion, standard activity basic alumina (∼0.5 g) was added, and the solution was allowed to
stir for 20 min. After this time, the solution was filtered to remove the added alumina and
reduced under vacuum for purification.
Compound 6-1. 1,4-Phenylene diamine (1.000 g, 9.25 mmol), sodium tert -butoxide (5.33 g,
55.5 mmol), and bis- (dibenzylideneacetone)palladium (106 mg, 0.184 mmol) were added to a
round-bottom flask. This flask was sealed under an argon atmosphere. Anhydrous toluene (50.0
mL), 4-bromoanisole (7.61 g, 40.7 mmol), and tri-tert-butylphosphine (29.9 mg, 0.148 mmol,
added as a stock solution in toluene) were added. This mixture was refluxed under an inert
atmosphere for 2 h. Upon cooling, acidic clay (10.0 g, Montmorillonite K10) and acidic alumina
(1.00 g, standard basic) were added to the mixture. This slurry was filtered, washing with toluene
to yield a clear, pale yellow solution. This solution was concentrated under vacuum and
precipitated into methanol. 4.24 g of a fine pale white powder was obtained (86% yield): 1H
NMR (400
MHz, C6D6) δ 7.14 (d, J = 9.08 Hz, integration obscured by solvent peak), 7.08 (s, 4H), 6.73 (d, J
= 9.08 Hz, 8H), 3.30 (s, 12H); 13C NMR (100 MHz, C6D6) δ 156.3, 143.8, 142.6, 126.4, 124.2,
115.5, 53.4; HRMS (ESI) [M+] calcd for C34H32N2O4 532.2356, found 532.2372.
Compound 6-2a. Using the general P−R procedure, 6-1 (500 mg, 0.939 mmol), anhydrous
toluene (10.0 mL), tris(pentafluorophenyl)-borane (5 mg, 0.01 mmol), and
pentamethyldisiloxane (3.14 g, 21.3 mmol) were reacted. After 20 min, the solution was
171
171
immersed in an oil bath at 50 °C. The solution vigorously evolved methane and was allowed to
continue to stir for 20 min. The product was purified by column chromatography over silica gel
eluting with 2:1 cyclohexane/toluene. 661 mg of a flakey crystalline solid was isolated (yield
66%): 1H NMR (400 MHz, C6D6) δ 7.09 (d, J = 8.98 Hz, 8H), 7.01 (s, 4H), 6.91 (d, J = 8.98 Hz,
8H), 0.22 (s, 24H), 0.11 (s, 36H); 13C NMR (100 MHz, C6D6) δ 151.0, 143.8, 143.3, 126.2,
124.6, 121.3, 2.1, 0.2; HRMS (ESI) [M + H] calcd for C50H81N2O8Si8 1061.4141, found
1061.4146.
Compound 6-2b. Using the general P−R procedure, compound 6-1 (0.500 g, 0.939 mmol),
1,1,1,3,5,5,5-heptamethyltrisiloxane (2.51 g, 11.3 mmol), tris(pentafluorophenyl)borane (5 mg,
0.01 mmol), and anhydrous toluene (5.00 mL) were reacted. The product was isolated by column
chromatography over silica gel eluting with 2:1 cyclohexane/toluene. A viscous yellow oil was
isolated (1.034 g, 81% yield): 1H NMR (400 MHz, C6D6) δ 7.10 (d, J = 8.77 Hz, 8H), 7.07 (s,
4H), 6.97 (d, J = 8.77 Hz, 8H), 0.27 (s, 12H), 0.15 (s, 72H); 13C NMR (100 MHz, C6D6) δ 150.2,
143.4, 143.1, 125.9, 124.1, 120.9, 1.7, −3.0; HRMS (ESI) [M+] calcd for C58H104N2O12Si12
1356.4821, found 1356.4814.
Compound 6-3a. Aniline (5.98 g, 64.2 mmol), 4-bromoanisole (10.0 g, 53.5 mmol), sodium tert-
butoxide (7.71 g, 80.2 mmol), bis(dibenzylideneacetone)palladium (154 mg, 0.268 mmol), tri-
tertbutylphosphine (43.0 mg, 0.212 mmol, as a 10 g/L solution in toluene), and anhydrous
toluene (75.0 mL) were added to a round bottom flask. The flask was refluxed for 2 h under
argon gas. Once cool, acid-washed clay (montmorillonite K10 from Sigma Aldrich, 10.0 g) and
standard basic alumina (1.00 g) were added to the slurry and stirred for 30 min. The slurry was
filtered, and the clear light yellow mother liquor was collected. This organic phase was washed
with 10% HCl solution three times and with brine once and then dried over magnesium sulfate.
The organic phase was concentrated under vacuum and recrystallized from boiling heptanes to
yield small silver needles. 7.43 g of product was isolated (67% yield): 1H NMR (400 MHz,
C6D6) δ 7.23 (t, J = 7.99 Hz, 2H), 7.09 (d, J = 8.57 Hz, 2H), 6.95−6.82 (m, 5H), 5.50 (s, broad,
1H), 3.81 (s, 3H).
172
172
Compound 6-3b. Using the same general procedure as for compound 6-3a above, p-toluidine
(6.88 g, 64.2 mmol), 4-bromoanisole (10.0 g, 53.5 mmol), sodium t-butoxide (7.71 g, 80.2
mmol),
bis(dibenzylideneacetone)palladium (154 mg, 0.268 mmol), tri-tertbutylphosphine (43 mg, 0.212
mmol), and anhydrous toluene (75.0 mL) were reacted at reflux for 2 h. Product recrystallized
from heptanes to yield light brown flakes. 7.26 g of pure product was isolated (64% yield): 1H
NMR (400 MHz, CDCl3) δ 7.06−7.00 (m, 4H), 6.88−6.82 (m, 4H), 5.39 (s, broad, 1H), 3.80 (s,
3H), 2.28 (s, 3H).
Compound 6-3c. Using the same general procedure as for compound 6-3a above, 3,4-
dimethylaniline (3.56 g, 29.4 mmol), 4-bromoanisole (5.00 g, 26.7 mmol), sodium t-butoxide
(3.84 g, 40.0 mmol), bis(dibenzylideneacetone)palladium (154 mg, 0.268 mmol), tri-tert-
butylphosphine (43 mg, 0.212 mmol), and anhydrous toluene (35.0 mL) were refluxed for 2 h.
Product recrystallized from heptanes to yield silver needles. 4.50 g of pure product was isolated
(67% yield): 1H NMR (400 MHz, CDCl3) δ 7.05−6.95 (m, 3H), 6.83 Hz (d, J = 8.96 Hz, 2H),
6.76−6.64 (m, 2H), 5.33 (s, broad, 1H), 3.78 (s, 3H), 2.19 (s, 6H).
Compound 6-3d. Using the same general procedure as for compound 6-3a above, 2-bromo-6-
methoxynaphthalene (10.0 g, 42.2 mmol), para-anisidine (6.23 g, 50.6 mmol), sodium t-butoxide
(5.95 g, 61.9 mmol), bis(dibenzylideneacetone)palladium (119 mg, 0.207 mmol), tri-tert-
butylphosphine (33 mg, 0.163 mmol), and anhydrous toluene (50.0 mL) were refluxed for 1 h.
Product recrystallized from heptanes to yield fine gray needles (5.54 g, 47% yield): 1H NMR
(400 MHz, CDCl3) δ 7.53 (d, J = 9.00 Hz, 1H), 7.39 (d, J = 0.99 Hz, 1H), 7.18 (dd, J1 = 11.35
Hz, J2 = 2.74 Hz, integration obscured by residual solvent peak), 7.02−6.91 (m, 4H), 6.79 (d, J =
8.61 Hz, 2H), 5.01 (s, broad, 1H), 3.44 (s, 3H), 3.37 (s, 3H). NMR (100 MHz, C6D6) δ 156.81,
156.09, 141.91, 137.09, 131.20, 130.49, 128.60, 128.50, 122.48, 120.45, 119.88, 115.42, 111.25,
106.85, 55.48, 55.19; HRMS (ESI) [M+ H] calcd for C18H18NO2 280.1338, found 280.1346.
Compound 6-4a. Compound 6-3a (3.00 g, 15.1 mmol), 4,4′-dibromobiphenyl (2.24 g, 7.17
mmol), sodium tert-butoxide (2.07 g, 21.5 mmol), palladium(II) acetate (16 mg, 0.0713 mmol),
tri-tertbutylphosphine (16 mg, 0.0791 mmol, added as a stock solution in toluene), and
173
173
anhydrous toluene (25 mL) were added to a round bottom flask. This solution was refluxed for 1
h under an argon atmosphere. Upon cooling, acid-washed clay (montmorillonite K10 from
Sigma Aldrich, 2.00 g) and standard activity basic alumina (0.500 g) were added and allowed to
stir into the mixture for 10 min. The solids were filtered out, washing with additional toluene.
The mother
liquor was collected and concentrated under vacuum until the solution began to become a
viscous oil. This oil was precipitated into rapidly stirring methanol (50 mL) to yield a fine white
powder. This powder was collected by filtration and washed with cold methanol. 2.635 g of
product was isolated (67% yield): 1H NMR (400 MHz, C6D6) δ 7.41 (d, J = 8.61 Hz, 4H),
7.19−7.13 (m, peak obscured by solvent peak), 7.10 (d, J = 7.41 Hz, 4H), 7.06 (d, J = 9.00 Hz,
4H), 6.85 (t, J = 7.04 Hz, 2H), 6.71 (d, J = 9.00 Hz, 4H), 3.29 (s, 6H).
Compound 6-4b. Using the same general procedure as for compound 6-4a, compound 6-3b (3
g, 14.1 mmol), 4,4′-dibromobiphenyl (2.09 g, 6.67 mmol), sodium tert-butoxide (1.93 g, 20.1
mmol),
palladium(II) acetate (15 mg, 0.0668 mmol), tri-tert-butylphosphine (11 mg, 0.0544 mmol,
added from stock solution in anhydrous toluene), and anhydrous toluene (25.0 mL) were reacted
for 2 h at reflux. 7.06 g of isolated material was collected (87% yield): 1H NMR (400 MHz,
C6D6) δ 7.43, (d, J = 8.77 Hz, 4H), 7.11 (d, J = 8.77 Hz, integration obscured by solvent),
7.15−7.08 (m, integration obscured by solvent), 6.94 (d, J = 7.99 Hz, 4H) 6.72 (d, J = 8.96 Hz,
4H), 3.30 (s, 6H), 2.12 (s, 6H); 13C NMR (100 MHz, C6D6) δ 156.7, 147.9,146.3, 141.5, 134.4,
132.1, 130.3, 127.6, 127.4, 124.4, 123.0, 115.2, 55.0, 20.8; HRMS (EI) [M+] calcd for
C40H36N2O2 576.2777, found 576.2769.
Compound 6-4c. Using the same general procedure as for compound 6-4a, compound 6-3c
(6.41 g, 28.2 mmol), 4,4′-dibromobiphenyl (4.00 g, 12.8 mmol), sodium tert-butoxide (3.08 g,
32.0 mmol), palladium(II) acetate (115 mg, 0.512 mmol), tri-tert-butylphosphine (83 mg, 0.410
mmol, added from stock solution in anhydrous toluene), and anhydrous toluene (25.0 mL) were
reacted for 3 h at reflux. The compound precipitated poorly in methanol and was purified by
column chromatography over silica gel eluting with 1:1 cyclohexane/toluene. A fine white
powder was collected (5.21 g, 67%): 1H NMR (400 MHz, C6D6) δ 7.44 (d, J = 8.96 Hz, 4H),
174
174
7.22 (d, J = 8.77 Hz, 4H), 7.15 (d, integration and coupling obscured by residual solvent peak),
7.11 (d, J = 2.14 Hz, 2H), 7.03 (dd, J1 = 8.18 Hz, J2 = 2.14 Hz, 2H), 6.94 (d, J = 8.18 Hz, 2H),
6.73 (d, J = 8.96 Hz, 4H), 3.30 (s, 6H), 2.03 (s, 6H), 1.93 (s, 6H). 13C NMR (100 MHz, C6D6) δ
156.6, 148.0, 146.6, 141.7, 137.7, 134.3, 131.0, 130.9, 127.6, 127.3, 126.0, 122.8, 122.4, 115.2,
55.0, 19.8, 19.1; HRMS (ESI) [M+] calcd for C42H40N2O2 604.3090, found 604.3100.
Compound 6-4d. Using the same general procedure as for compound 6-4a, bis(4-
methoxyphenyl)amine (3.82 g, 16.8 mmol), 4,4′-dibromobiphenyl (2.50 g, 8.01 mmol), sodium t-
butoxide (1.92 g, 20.0 mmol), palladium(II) acetate (72 mg, 0.321 mmol), tri-tertbutylphosphine
(52 mg, 0.257 mmol, added from stock solution in anhydrous toluene), and anhydrous toluene
(20.0 mL) were reacted for 3 h at reflux. The compound was precipitated into methanol and
recrystallized from EtOAc. Slightly yellow flakes were collected (3.33 g, 70%): 1H NMR (400
MHz, C6D6) δ 7.46 (d, J = 8.61 Hz, 4H), 7.17 (m, obscured by residual solvent), 7.12 (d, J = 9.00
Hz, 8H), 6.74 (d, J = 9.00 H, 8H), 3.31 (s, 12H); 13C NMR (100 MHz, C6D6) δ 156.4, 148.2,
141.7, 134.0, 127.6, 126.8, 122.0, 115.17, 55.0.
Compound 6-4e. Using the same general procedure as for compound 6-4a, 6-3d (2.43 g, 8.71
mmol), 4,4′-dibromobiphenyl (1.35 g, 4.34 mmol), sodium t-butoxide (1.29 g, 13.4 mmol),
palladium(II)
acetate (13 mg, 0.0579 mmol), tri-tert-butylphosphine (9 mg, 0.046 mmol), and anhydrous
toluene (15.0 mL) were refluxed for 1 h. Compound was precipitated into methanol to yield a
fine white powder. The product was further purified by recrystallization from toluene/EtOAc to
yield small white crystals (2.66 g, 86% yield): 1H NMR (400 MHz, C6D6) δ 7.56 (d, J = 1.96 Hz,
2H), 7.52 (d, J = 9.00 Hz, 2H), 7.47 (d, J = 8.61 Hz, 4H), 7.42 (dd, J1 = 9.00 Hz, J2 = 2.35
Hz, 2H), 7.27−7.22 (m, 6H), 7.17−7.09 (m, integration obscurd by residual solvent peak), 6.94
(d, J = 2.35 Hz, 2H), 6.75 (d, J = 9.00 Hz, 4H), 3.40 (s, 6H), 3.32 (s, 6H); 13C NMR (100 MHz,
C6D6) δ 157.8, 157.1, 148.2, 144.8, 144.8, 135.0, 131.9, 130.9, 129.3, 128.5, 128.1, 127.8, 125.6,
123.6, 121.1, 119.8, 115.7, 106.6, 55.4, 55.2; HRMS (ESI) [M + H] calcd for C48H41N2O4
709.3066, found 709.3048.
175
175
Compound 6-5a. Using the general P−R procedure, 6-4a (0.500 g 0.937 mmol),
tris(pentafluorophenyl)borane (5 mg, 0.00977 mmol), and 5.00 mL of toluene were stirred, and
pentamethyldisiloxane (1.35 g, 9.11 mmol) was added dropwise. The reaction proceeded
vigorously and was allowed to stir for an additional 20 min after bubbling had ceased. The
product was purified by column chromatography over silica gel eluting with 5:2
cyclohexane/toluene. The product was isolated as a viscous pale yellow oil (0.391 g, 51% yield): 1H NMR (400 MHz, C6D6) δ 7.38 (d, J = 8.77 Hz, 4H), 7.16−7.12 (m, integration obscured by
solvent), 7.12−7.02 (8H), 6.92 (d, J = 9.16 Hz, 4H), 6.84 (t, J = 7.21 Hz, 2H), 0.23 (s, 12H), 0.12
(s, 18H); 13C NMR (100 MHz, C6D6) δ 151.5, 148.7, 147.6, 142.2, 135.0, 129.6, 127.7, 127.3,
123.9, 123.9, 122.5, 121.1, 1.8, −0.2; HRMS (ESI) [M+] calcd for C46H56N2O4Si4 812.3317,
found 812.3300.
Compound 6-5b. Using the general P−R procedure, 6-4b (0.500 g, 0.867 mmol),
pentamethyldisiloxane (1.29 g, 8.67 mmol), tris(pentafluorophenyl)borane (5 mg, 0.00977
mmol), and anhydrous toluene (5.00 mL) were reacted at room temperature; the reaction
proceeded vigorously. The compound was purified by column chromatography eluting with 5:2
cyclohexane/toluene. The product was isolated as a viscous and pale yellow oil (0.350 g, 48%
yield): 1H NMR (400 MHz, C6D6) δ 7.40 (d, J = 8.77 Hz, 4H), 7.18 (m, obscured by solvent),
7.13−7.06 (m, 8H), 6.97−6.89 (m, 8H), 2.11 (s, 6H), 0.23 (s, 12H), 0.12 (s, 18H); 13C NMR (100
MHz, C6D6) δ 151.2, 147.8, 146.2, 142.5, 134.6, 132.2, 130.3, 127.6, 126.9, 124.7, 123.3, 121.0,
20.8, 1.8, −0.1; HRMS (ESI) [M+] calcd for C48H60N2O4Si4 840.3630, found 840.3639.
Compound 6-5c. Using the general P−R procedure, 6-4c (0.500 g, 0.827 mmol),
pentamethyldisiloxane (0.490 g, 3.30 mmol), tris(pentafluorophenyl)borane (4 mg, 0.00781
mmol), and anhydrous toluene (5.00 mL) were reacted. The product was purified by column
chromatography eluting with 5:2 cyclohexane/toluene. The product was isolated as a viscous and
pale yellow oil (0.467, 65% yield): 1H NMR (400 MHz, C6D6) 7.41 (d, J = 8.96 Hz, 4H), 7.2 (d,
J = 8.57 Hz, 4H), 7.13 (d, 8.96 Hz, 4H), 7.08 (d, J = 2.14 Hz, 2H), 7.01 (dd, J1 = 5.65 Hz, J2 =
2.14 Hz, 2H), 6.97−6.91 (m, 6H), 2.02 (s, 6H), 1.92 (s, 6H), 0.23 (s, 12H), 0.12 (s, 18H); 13C
NMR (100 MHz, C6D6) δ 151.1, 147.9, 146.5, 142.7, 137.7, 134.5, 131.2, 130.9, 127.6, 126.8,
176
176
126.3, 123.2, 122.7, 121.0, 19.8, 19.1, 1.9, −0.1; HRMS (ESI) [M+] calcd for C50H64N2O4Si4
868.3943, found 868.3930.
Compound 6-5d. Using the general P−R procedure, 6-4d (0.500 g, 0.821 mmol),
pentamethyldisiloxane (0.975 g, 6.57 mmol), tris(pentafluorophenyl)borane (4 mg, 0.00781
mmol), and 10.0 mL of anhydrous toluene were reacted. The product was purified by passing the
compound through a plug of silica gel eluting with 1:1 hexanes/toluene. A clear oil was obtained,
which slowly crystallized to soft white crystals after several days (0.860 g, 92% yield): 1H NMR
(400 MHz, C6D6) δ 7.40 (d, J = 8.77 Hz, 4H), 7.14 (partially obscured by solvent peak), 7.08 (d,
J = 8.96 Hz, 8H), 6.93 (d, J = 8.96 Hz, 8H), 0.23 (s, 24H), 0.12 (s, 36H); 13C NMR (100 MHz,
C6D6) δ 151.0, 148.0, 142.6, 134.3, 127.6, 126.5, 122.8, 121.0, 1.8, −0.2; HRMS (ESI) [M+]
calcd for C56H84N2O8Si8 1136.4382, found 1136.4368.
Compound 6-5e. Using the general P−R procedure, 6-4b (0.500 g, 0.867 mmol), 1,1,1,3,5,5,5-
heptamethyltrisiloxane (1.930 g, 8.67 mmol), tris(pentafluorophenyl)borane (4 mg, 0.00781
mmol), and anhydrous toluene (5 mL) were reacted at room temperature; the reaction proceeded
rapidly. The compound was purified by column chromatography eluting with 5:2
cyclohexane/toluene. The final product was isolated as a viscous clear oil (0.592 g, 69% yield): 1H NMR (400 MHz, C6D6) δ 7.41 (d, J = 8.77 Hz, 4H), 7.18 (d, J = 8.96 Hz, integration obscured
by solvent), 7.13−7.07 (m, 8H), 7.00 (d, J = 8.96 Hz, 4H), 6.92 (d, J = 8.77 Hz, 4H), 2.11 (s, 6H),
0.28 (s, 6H), 0.17 (s, 36H); 13C NMR (100 MHz, C6D6) δ 150.8, 147.8, 146.2,
142.6, 134.6, 132.2, 130.3, 127.7, 126.9, 124.6, 123.2, 121.0, 20.8, 1.7, −3.0; HRMS (ESI) [M+]
calcd for C52H72N2O6Si6 988.4006, found 988.3995.
Compound 6-5f. Using the general P−R procedure, 6-4d (0.500 g, 0.821 mmol), 1,1,1,3,5,5,5-
heptamethyltrisiloxane (1.46 g, 6.57 mmol), tris(pentafluorophenyl)borane (4 mg, 0.00781
mmol), and anhydrous toluene (10.0 mL) were reacted. Compound was purified by column
chromatography eluting with 1:1 cyclohexane/toluene. The final product was isolated as a pale
yellow oil (1.06 g, 90% yield): 1H NMR (400 MHz, C6D6) δ 7.43 (d, J = 8.77 Hz, 8H), 7.16
(multiplicity and integration obscured by solvent peak), 7.09 (d, J = 8.77 Hz, 8H), 7.00 (d, J =
8.96 Hz, 4H), 0.28 (s, 12H), 0.16 (s, 72H); 13C NMR (100 MHz, C6D6) δ 150.6, 148.0, 142.8,
177
177
134.3, 127.6, 128.5, 122.7, 121.0, 1.7, −3.0; HRMS (ESI) [M+] calcd for C64H108N2O12Si12
1432.5134, found 1432.5153.
Compound 6-5g. Using the general P−R procedure, 6-4e (0.500 g, 0.705 mmol),
pentamethyldisiloxane (1.05 g, 7.06 mmol), tris(pentafluorophenyl)borane (4 mg, 0.00781
mmol), and toluene (10.0 mL) were reacted. Compound was purified by column chromatography
eluting with 1:1 cyclohexane/toluene to yield a slightly green powder (0.426 g, 49% yield): 1H
NMR (400 MHz, C6D6) δ 7.54 (d, J = 2.14 Hz, 2H), 7.47 (d, J = 9.2 Hz, 2H), 7.44 (d, J = 8.77
Hz, 4H), 7.42 (d, J = 2.34 Hz, 2H), 7.34 (dd, J1 = 8.96 Hz, J2 = 2.34 Hz, 2H), 7.26 (d, J = 8.96
Hz, 2H), 7.20 (d, J = 8.77 Hz, 4H), 7.16 (obscured by solvent peak), 7.11 (d, J = 8.77 Hz, 4H),
6.97 Hz (d, J = 8.96 Hz, 4H), 0.27 (s, 12H), 0.24 (s, 12H), 0.14 (s, 12H), 0.13 (s, 12H); 13C NMR
(100 MHz, C6D6) δ 152.5, 151.7, 148.1, 145.0, 142.7, 135.2, 132.1, 131.4, 129.3, 127.4, 125.8,
124.0, 122.8, 121.4, 121.4, 115.6, 2.2, 2.2, 0.2, 0.1; HRMS (ESI) [M + H] calcd for
C64H89N2O8Si8 1237.4773, found 1237.4715.
Compound 6-5h. Using the general P−R procedure, 6-4e (400 mg, 0.564 mmol), 1,1,1,3,5,5,5-
heptamethyltrisiloxane (748 mg, 3.36 mmol), tris(pentafluorophenyl)borane (3 mg, 0.00587
mmol), and toluene (10.0 mL) were reacted. Compound purified by column chromatography
eluting with 1:1 cyclohexane/toluene to yield a viscous clear oil (803 mg, 93% yield): 1H NMR
(400 MHz, C6D6) δ 7.53−7.47 (m, 6H), 7.43 (d, J = 8.61 Hz, 4H), 7.34 (dd, J1 = 9.00 Hz,
J2 = 1.96 Hz, 2H), 7.30 (d, J = 9.00 Hz, 2H), 7.22 (dd, J1= 9.00 Hz, J2 =2.35 Hz, 2H), 7.19 (d, J
= 8.61 Hz, 4H), 7.07 (d, J = 9.00 Hz, 4H), 7.01 (d, J = 9.00 Hz, 4H), 0.32 (s, 6H), 0.29 (s, 6H),
0.17 (s, 72H); 13C NMR (100 MHz, C6D6) δ 152.0, 151.3, 148.0, 145.0, 142.8, 135.2, 132.0,
131.4, 129.2, 127.5, 125.7, 124.0, 122.6, 121.5, 121.1, 115.5, 2.12, 2.10, −2.6, −2.7; HRMS
(ESI) [M + H] calcd for C72H113N2O12Si12 1533.5519, found 1533.5583.
Compound 6-6. 2-Bromobiphenyl (5.00 g, 21.4 mmol) in anhydrous THF (11.0 mL) was
reacted with magnesium (0.567 g, 23.3 mmol) under inert gas at room temperature. Upon
formation of the Grignard reagent, 9-fluorenone (3.90 g, 21.6 mmol in 5.00 mL of THF) was
added, and the solution was refluxed for 4 h and allowed to cool. Upon cooling, a yellow
precipitate was formed and collected, washing with cold methanol. This solid was stirred into a
178
178
5% HCl solution (22.0 mL) for 2 h at room temperature and washed with additional methanol.
Finally, the solid was dissolved in acetic acid (22.0 mL) and refluxed for 40 min. Upon cooling,
large white crystals
of the pure product were obtained (3.73 g, 56% yield).
Compound 6-7. Compound 6-6 (1.00 g, 3.16 mmol), FeCl3 (2 mg, 0.0123 mmol), and 6 mL of
chloroform were mixed under an inert atmosphere. Molecular bromine (2.02 g, 12.6 mmol) in
2.00 mL of chloroform was added, and the reaction was allowed to proceed at room temperature
in the absence of light for 5 days. Upon completion, the reaction was quenched with aqueous
ammonium hydroxide and recrystallized from chloroform/ethanol (50/50 to yield a pure white
crystalline product (1.10 g, 55% yield).
Compound 6-8. Palladium(II) acetate (5 mg, 0.0223 mmol), 7(200 mg, 0.316 mmol), 6-3b (340
mg, 1.59 mmol), sodium tert-butoxide (145 mg, 1.51 mmol), and 2.30 mL of anhydrous toluene
were added to a round-bottom flask under an atmosphere of argon. Once sealed, tri-tert-
butylphosphine (3.75 mg, 0.0185 mmol) was added as a toluene stock solution. The mixture was
refluxed for 5 h under argon and allowed to cool. The solution was filtered through a short plug
of silica to yield a clear yellow liquid; this solution was concentrated and precipitated into
stirring methanol to yield the product as a fine white powder (258 mg, 67% yield): 1H NMR (400
MHz, C6D6) δ 7.12 (dd, J1 = 7.82 Hz, J2 = 2.93 Hz, 8H), 7.09−7.01 (m, 16H), 7.00 (dd, J1 =
8.22 Hz, J2 = 2.35 Hz, 4H), 6.95 (d, J = 8.22, 8H), 6.71 (d, J = 9.39 Hz, 8H), 3.25 (s, 12H), 2.05
(s, 12H); 13C NMR (100 MHz, C6D6) δ 156.7, 151.1, 148.2, 146.9, 141.94, 135.6, 131.7, 130.3,
127.2, 124.0, 123.5, 121.1, 119.2, 115.4, 66.8, 55.3, 21.1. MS (ESI) [M+] calcd for
C81H68N4O8 1160.5, found 1160.5
Compound 6-9. Using the general P−R procedure, 11 (200 mg, 0.172 mmol), 1,1,1,3,5,5,5-
heptamethyltrisiloxane (445 mg, 2.00 mmol), 2.00 mL of toluene, and
tris(pentafluorophenyl)borane (1 mg, 0.00195 mmol) were reacted at room temperature.
Compound was purified by column chromatography on silica gel eluting with hexanes/toluene.
Product was isolated as a glass (294 mg, 86% yield): 1H NMR (400 MHz, C6D6) δ 7.18 (signal
obscured by solvent), 7.09 (d, J = 2.35 Hz, 4H), 7.05−6.95 (m, 36H), 2.05 (s, 12H), 0.28 (s,
179
179
12H), 0.14 (s, 72H). 13C NMR (100 MHz, C6D6) δ 151.0, 150.9, 148.1, 146.6, 143.0, 136.4,
132.2, 130.4, 126.8, 124.3, 123.5, 121.2, 120.8, 118.8, 66.8, 21.2, 2.1, −2.6; MS (ESI) [M + 3H]
calcd for C106H145N4O11Si12 1984.8, found 1987.8.
Compound 6-10. Tris(4-bromophenyl)amine (0.500 g, 1.04 mmol), compound 6-3c (0.786 g,
3.46 mmol), sodium t-butoxide (0.444 g, 4.63 mmol), palladium(II) acetate (5 mg, 0.00223
mmol), tri-tertbutylphosphine (3 mg, 0.00148 mmol), and anhydrous toluene (10.0 mL) were
refluxed for 16 h. Upon cooling, the mixture was filtered, and the resulting liquor was
concentrated and precipitated into methanol to yield a light yellow fine powder (742 mg, 78%
yield): 1H NMR (400 MHz, C6D6) δ 7.16−7.12 (m, integration obscured by residual solvent),
7.10−7.06 (m, 9H), 7.02 (dd, J1 = 8.02 Hz, J2 = 2.54 Hz, 3H), 6.92 (d, J = 8.22 Hz, 3H), 6.71 (d,
J = 9.00 Hz, 6H); 13C NMR (100 MHz, C6D6) δ 156.6, 147.2, 144.3, 143.1, 142.3, 137.9, 131.1,
130.8, 127.2, 125.7, 125.5, 124.5, 122.0, 115.5, 55.4, 20.2, 19.4; HRMS (ESI) [M + H] calcd for
C63H61N4O3 921.4744, found 921.4765.
Compound 6-11. Using the general P−R procedure, compound 6-10 (0.349 g, 0.379 mmol),
1,1,1,3,5,5,5-heptamethyltrisiloxane (0.871 g, 3.91 mmol), tris(pentafluorophenyl)borane (2 mg,
0.00391 mmol), and 5.00 mL of toluene were reacted for 16 h under ambient conditions. Product
was purified by column chromatography eluting with hexanes/toluene and isolated as a white
crystalline solid (269 mg, 46% yield): 1H NMR (400 MHz, C6D6) δ 7.14−7.09 (m, 12H), 7.08−
7.04 (m, 9H), 7.02−6.95 (m, 9H), 6.91 (d, J = 8.22 Hz, 3H), 2.01 (s, 9H), 1.92 (s, 9H), 2.07 (s,
9H), 0.15 (s, 54H); 13C NMR (100 MHz, C6D6) δ 150.7, 147.1, 144.2, 143.3, 143.1, 137.9, 131.1,
130.9, 126.7, 126.0, 125.4, 124.7, 122.3, 121.3, 20.15, 19.4, 2.1, −2.7; HRMS (ESI)
[M + H] calcd for C81H115N4O9Si9 1539.6587, found 1539.6546.
Compound 6-12a. In an inert atmosphere glovebox, 4-bromo-3-nitroanisole (3.00 g, 12.9
mmol), phenylboronic acid (1.73 g, 14.2 mmol ) , cesium fluoride (3.93 g, 25.8 mmol), bis-
(dibenzylideneacetone)palladium (149 mg, 0.258 mmol), tri-tertbutylphosphine (52 mg, 0.258
mmol, added as a 10 g/L stock solution in anhydrous toluene), and anhydrous tetrahydrofuran
(60.0 mL) were added to a stirred round-bottom flask. This flask was allowed to stir at ambient
temperature for 24 h. The resulting solution was removed from the glovebox, and the solids were
180
180
filtered, eluting with THF. This light brown solution was dried under vacuum. The remaining
solids were taken up in toluene and washed with water and brine. The organic toluene phase was
dried over magnesium sulphate and filtered through a short plug of silica gel, eluting with
toluene. This light-yellow liquid was concentrated under vacuum until it resembled a viscous oil.
Hexanes (5.00 mL) were added to this resulting oil to precipitate light yellow crystals. These
crystals were collected and washed with cold hexanes and then dried under vacuum (2.44 g
collected, 85% yield): 1H NMR (400 MHz, CDCl3) δ 7.43−7.32 ppm (m, 5H), 7.30−7.25 (m,
2H), 7.15 (dd, J1 = 8.6 Hz, J2 = 2.7 Hz, 1H), 3.90 (s, 3H); 13C NMR (100 MHz, CDCl3) δ 159.2,
137.4, 132.9, 128.80, 128.76, 128.2, 128.0, 118.8, 109.2, 56.1; HRMS (EI) [M+] calcd for
C13H11NO3 229.0733, found 229.0739.
Compound 6-12b. In an inert atmosphere glovebox, 4-bromo-3-nitroanisole (3.47 g, 15.0
mmol), 4-methoxyphenylboronic acid (2.50 g, 16.5 mmol), cesium fluoride (7.52 g, 49.5 mmol),
bis- (dibenzylideneacetone)palladium (259 mg, 0.45 mmol), tri-tertbutylphosphine (91 mg, 0.450
mmol, added as a 10 g/L stock solution in anhydrous toluene), and anhydrous tetrahydrofuran
(30.0 mL) were added to a stirred round-bottom flask. This flask was allowed to stir at ambient
temperature for 24 h. The resulting solution was removed from the glovebox, and the solids were
filtered, eluting with THF. This light brown solution was dried under vacuum. The remaining
solids were taken up in toluene and washed with water and brine. The organic toluene phase was
dried over magnesium sulphate and filtered through a short plug of silica gel, eluting with
toluene. This light yellow liquid was then concentrated under vacuum until it resembled a
viscous oil. Hexanes (5.00 mL) were added to this resulting oil, and the solution was cooled in a
refrigerator overnight. Light-yellow crystals were collected and washed with cold hexanes and
then dried under vacuum (2.55 g collected, 65% yield). This product was used without further
purification: 1H NMR (400 MHz, CDCl3) δ 7.34−7.30 (m, 2H), 7.21 (d, J = 8.96 Hz, 2H), 7.13
(dd, J1 = 8.57 Hz, J2 = 2.73 Hz, 1H), 6.96 (d, J = 8.96 Hz, 2H), 3.89 (s, 3H), 3.84 (s, 3H); 13C
NMR (100 MHz, CDCl3) δ 159.5, 159.0, 132.9, 129.6, 129.3, 128.4, 118.8, 114.3, 109.0, 104.9,
56.1, 55.4; HRMS (ESI) [M+] calcd for C14H13NO4 259.0845, found 259.0845.
Compound 6-13a. Compound 6-12a (2.20 g, 9.56 mmol) was added to a stirred round-bottom
flask, and the flask was flushed with argon gas and sealed under a positive pressure of gas.
181
181
Triethylphosphite (7.70 mL) was added via syringe, and the solution was heated at 160 °C for 16
h. The reaction was allowed to cool, and 10.0 mL of methanol was added to the solution. This
was allowed to rest in a refrigerator overnight to yield white square crystals. These crystals were
collected by filtration and washed sparingly with cold methanol. The collected crystals were then
dried under vacuum (1.69 g was isolated, 56% yield): 1H NMR (400 MHz, (CD3)2SO) δ 11.10 (s,
broad, 1H), 7.98 (m, 2H), 7.41 (d, J = 7.82 Hz, 1H), 7.28 (td, J1 = 7.63 Hz, J2 = 1.17 Hz, 1H),
7.10 (td, J1 = 7.82 Hz, J2 = 1.17 Hz, 1H), 6.96 (d, J = 2.35, 1H), 6.76 (dd, J1 =8.61 Hz, J2 = 2.35
Hz, 1H), 3.84 (s, 3H); 13C NMR (100 MHz, (CD3)2SO) δ 158.4, 141.0, 139.7, 124.0, 122.6,
120.9, 119.2, 118.5, 116.1, 110.6, 107.6, 94.4, 55.2; HRMS (ESI) [M + H] calcd for C13H12NO
198.0913, found 198.0906.
Compound 6-13b. Compound 6-12b (2.55 g, 9.81 mmol) and triethylphosphite (8.90 mL) were
heated at 160 °C for 16 h under argon. The reaction was allowed to cool, and 10.0 mL of
methanol was added to the solution. This was allowed to rest in a refrigerator overnight to yield
small white needles. These crystals were collected by filtration and washed sparingly with cold
methanol. The resulting white crystals were then dried under vacuum (1.83 g, 82% yield): 1H
NMR (400 MHz, (CD3)2SO) δ 10.94 (s, broad, 1H), 7.83 (d, J = 8.38 Hz, 2H), 6.92 (d, J = 2.14
Hz, 2H), 6.72 (dd, J1 = 8.38 Hz, J2 = 2.14 Hz, 2H); 13C NMR (100 MHz, (CD3)2SO) δ 157.5,
141.0, 119.9, 116.4, 107.3, 94.6, 55.2; HRMS (ESI) [M + H] calcd for C14H14NO2 228.1019,
found 228.1011
Compound 6-14a. Iodobenzene (1.241 g, 6.08 mmol), copper(I) iodide (77 mg, 0.404 mmol),
compound 6-13a (0.800 g, 4.06 mmol), L-proline (94 mg, 0.816 mmol), and potassium carbonate
(1.12 g, 8.10 mmol) were added to a stirred round-bottom flask. DMSO (7.00 mL) was added to
the flask, and the solution was sparged with argon gas for 30 min. The solution was heated to
180 °C for 1 h. After the solution was cool, toluene was added (25.0 mL), and any solids were
removed by filtration. The light brown liquor was concentrated under high vacuum to completely
remove any solvent and excess iodobenzene. The resulting solids were taken up in toluene and
passed through a short plug of silica, eluting with toluene. Solvent was removed under vacuum,
resulting in large flakey white crystals. These crystals were recrystallized from boiling heptanes
and dried under vacuum. 794 mg was isolated (72% yield): 1H NMR (400 MHz, CDCl3) δ 8.04
182
182
(dt, J1 = 7.83 Hz, J2 = 1.17 Hz, 1H), 8.00 (d, J = 8.22 Hz, 1H), 7.64−7.53 (m, 4H), 7.47 (m, 1H),
7.36−7.28 (m, 2H), 7.25 (m, 1H), 6.88 (td, J1 = 10.96 Hz, J2 = 2.35 Hz, 2H), 3.83 (s, 3H); 13C
NMR (100 MHz, CDCl3) δ 159.1, 142.2, 141.1, 137.7, 129.90, 127.5, 127.1, 124.6, 123.5, 121.0,
112.0, 119.4, 117.2, 109.5, 108.5, 94.0, 55.6; HRMS (ESI) [M + H] calcd for C19H16NO
274.1226, found 274.1227.
Compound 6-14b. Same general procedure as for compound 6-14a was used. Iodobenzene (1.0
g, 4.90 mmol), compound 13b (0.750 g, 3.27 mmol), copper(I) iodide (63 mg, 0.331 mmol), L-
proline (76 mg, 0.660 mmol), potassium carbonate (912 mg, 6.60 mmol), and 7.00 mL of DMSO
were reacted for 2 h. Product recrystallized from heptanes to yield white flakes. 821 mg of
product was isolated (82% yield): 1H NMR (400 MHz, CDCl3) δ 7.89 (d, J = 8.57 Hz, 2H), 7.61
(t, J = 7.41 Hz, 2H), 7.54 (d, J = 8.38 Hz, 2H), 7.47 (t, J = 7.41, 1H), 6.87 (dd, J1 = 8.38 Hz, J2 =
2.34 Hz, 2H), 6.82 (d, J = 2.34 Hz, 2H), 3.82 (s, 6H); 13C NMR (100 MHz, CDCl3) δ 158.3,
142.3, 137.6, 130.0, 127.5, 127.1, 120.1, 117.4, 108.2, 94.3, 55.7; HRMS (ESI) [M + H] calcd
C20H18NO2 304.1332, found 304.1340.
Compound 6-14c. Same general procedure as for compound 6-14a was used. 3-Iodoanisole
(10.92 g, 46.6 mmol), carbazole, (6.00 g, 35.9 mmol), copper(I) iodide (684 mg, 3.59 mmol), L-
proline (827 mg, 7.18 mmol), potassium carbonate (9.92 g, 71.8 mmol), and 60.0 mL of DMSO
were reacted for 3 h. Product recrystallized from heptanes and isolated as white flakes (7.75 g,
79% yield): 1H NMR (400 MHz, CDCl3) δ 8.14 (d, J = 7.75 Hz, 2H), 7.50 (t, J = 8.09 Hz, 1H),
7.45 (d, J = 7.99 Hz, 2H), 7.41 (t, d, J1 = 6.63 Hz, J2 = 1.36 Hz, 2H), 7.28 (ddd, J1 = 7.75 Hz, J2
= 6.63 Hz, J3 = 1.36 Hz, 2H), 7.16 (dq, J1 = 7.80 Hz, J2 = 0.97 Hz, 1H), 7.11 (t, J = 2.24 Hz,
1H), 7.01 (ddd, J1 = 8.38 Hz, J2 = 2.53 Hz, J3 = 0.97 Hz, 1H), 3.86 (s, 3H); 13C NMR (100
MHz, CDCl3) δ 160.8, 140.8, 138.8, 130.5, 125.9, 123.3, 120.3, 119.9, 119.3, 113.2, 112.6,
109.9, 55.5; HRMS (ESI) [M + H] calcd for C19H15NO 274.1226, found 274.1220.
Compound 6-14d. Same general procedure as for compound 6-14a was used. Carbazole (1.00 g,
5.98 mmol), 4-bromoanisole (1.34 g, 7.18 mmol), copper(I) iodide (114 mg, 0.599 mmol), L-
proline (138 mg, 1.20 mmol), potassium carbonate (1.653 g, 12.0 mmol), and DMSO (10.0 mL)
were added to a round-bottom flask. This solution was sparged with argon gas for 30 min and
183
183
then heated to 180 °C for 16 h. The reaction was diluted with toluene, and the solids were filtered
out. The mother liquor was passed through a plug of silica and then concentrated under high
vacuum and heat to remove the solvents, residual 4-bromoanisole and residual carbazole. The
resulting solids were recrystallized twice from boiling heptanes to yield long thin white needles.
685 mg were collected (42% yield): 1H NMR (400 MHz, CDCl3) δ 8.14 (d, J1 = 7.70 Hz 2H),
7.45 (d, 8.96 Hz, 2H), 7.40 (m, 2H), 7.32 (d, J = 8.38 Hz, 2H), 7.27 (t, J = 7.02 Hz, 2H), 7.11 (d,
J = 8.96 Hz, 2H), 3.92 (s, 3H); 13C NMR (100 MHz, CDCl3) δ 158.8, 141.4, 130.3, 128.6, 125.8,
123.1, 120.2, 119.6, 115.0, 109.7, 55.6; HRMS (ESI) [M+] calcd for C19H16NO 273.1148, found
273.1146.
Compound 6-15a. Using the general P−R procedure, tris(pentafluorophenyl)borane (10 mg,
0.0195 mmol), compound 6-14a (0.500 g, 1.82 mmol), and anhydrous toluene (5.00 mL) were
added to a open stirred vessel. 1,1,1,3,5,5,5-Heptamethyltrisiloxane (1.623 g, 7.32 mmol) was
added dropwise to this solution and allowed to stir for 20 min. Upon evaporation, a colorless oil
was obtained. This oil was diluted with hexanes and loaded onto a short plug of silica gel. This
plug was washed with hexanes (100 mL) and then washed with toluene. The toluene fraction was
collected and concentrated to yield a colorless oil (834 mg, 95% yield): 1H NMR (400 MHz,
C6D6) δ 8.00 (m, 1H), 7.93 (d, J = 8.61 Hz, 1H), 7.28−7.10 (m, integration obscured by solvent
peak), 7.04 (t, J = 7.43 Hz, 1H), 0.30 (s, 3H), 0.12 (s, 18H); 13C NMR (100 MHz, C6D6) δ 154.0,
142.8, 141.9, 138.2, 123.0, 127.5, 127.5, 125.2, 124.2, 121.4, 120.5, 120.1, 118.7, 113.8, 110.0,
101.0, 1.7, −3.1; HRMS (ESI) [M + H] calcd for C25H34NO3Si3 480.1841, found 480.1863.
Compound 6-15b. Using the general P−R procedure, compound 6-14b (0.500 g, 1.65 mmol),
tris(pentafluorophenyl)borane (9 mg, 0.176 mmol), 1,1,1,3,5,5,5-heptamethyltrisiloxane (2.90 g,
13.2 mmol), and anhydrous toluene (5.00 mL) were reacted. Product was purified by loading
onto a silica plug, washing first with hexanes and then washing with toluene. Product isolated as
a clear oil (1.00 g, 85% yield): 1H NMR (400 MHz, C6D6) δ 7.85 (d, J = 8.22 Hz, 2H), 7.21 (d, J
= 8.22 Hz, 2H), 7.19−7.11 (m, integration obscured by solvent), 7.04 (t, J = 7.43 Hz), 0.30 (s,
6H), 0.12 (s, 36H); 13C NMR (100 MHz, C6D6) δ 153.2, 143.1, 138.2, 130.1, 127.6, 127.6, 120.7,
118.9, 113.7, 101.1, 1.7, −3.1; HRMS (ESI) [M+] calcd for C32H53NO6Si6 715.2488, found
715.2486.
184
184
Compound 6-15c. Using the general P−R procedure, compound 6-14c (4.00 g, 14.6 mmol),
tris(pentafluorophenyl)borane (75 mg, 0.146 mmol), 1,1,1,3,5,5,5-heptamethyltrisiloxane (6.51
g, 29.2 mmol), and toluene (40.0 mL) were reacted. Product was purified by loading onto a silica
plug, washing first with hexanes and then washing with toluene. Product was isolated as a clear
oil (6.04 g, 86% yield): 1H NMR (400 MHz, CDCl3) δ 8.17 (d, J = 7.79 Hz, 2H), 7.50−7.40 (m,
5H), 7.00 (t, J = 7.00 Hz, 2H), 7.21 (dq, J1 = 7.80 Hz, J2 = 1.00 Hz, 1H), 7.17 (t, J = 1.95 Hz,
1H), 7.06 (ddd, J1 = 7.60 Hz, J2 = 2.34 Hz, J3 = 0.80 Hz,1H); 13C NMR (100 MHz, CDCl3) δ
155.5, 140.8, 138.6, 130.3, 125.9, 123.3, 120.3, 120.2, 119.8, 119.0, 118.7, 109.9, 1.6, −3.3;
HRMS (ESI) [M+] calcd for C25H33NO3Si3 479.1768, found 479.1755.
Compound 6-15d. Using the general P−R procedure, compound 6-14d (0.500 g, 1.83 mmol),
tris(pentafluorophenyl)borane (10 mg, 0.195 mmol), 1,1,1,3,5,5,5-heptamethyltrisiloxane (0.814
g, 3.66 mmol), and anhydrous toluene (5.00 mL) were reacted. Product was purified by loading
onto a silica plug, washing first with hexanes and then washing with toluene. Product was
isolated as a clear oil which crystallized into soft white needles after 2 months of storage
(728 mg, 83% yield): 1H NMR (400 MHz, CDCl3) δ 8.16 (d, J = 7.43 Hz, 2H), 7.45−7.38 (m,
4H), 7.34 (d, J = 7.82, 2H), 7.27 (t, J = 7.43 Hz, integration obscured by solvent peak), 7.14 (d, J
= 8.61 Hz, 2H), 0.28 (s, 3H), 0.15 (s, 18H); 13C NMR (100 MHz, CDCl3) δ 153.6, 141.3, 131.1,
128.4, 125.81, 123.1, 121.1, 120.2, 119.6, 109.7, 1.6, −3.2; HRMS (ESI) [M+] calcd for
C25H33NO3Si3 479.1768, found 479.1776.
12.4.2 Supplemental Information of Merit
Table S6-1: Lambda Max Comparison between Reference and Our Data (DCM vs Toluene)
Lambda Max for 1 (nm) Lambda Max for 4d (nm)
This Work (Toluene) 1056 1666
Reference Work (DCM) 1049 1572
Table S6-2: Estimated amount of oxidized arylamine from UV-VIS-NIR data.
185
185
Equivalents BCF Percent of Arylamine Oxidized Percent of BCF Reduced*
6-1 6-4d 6-1 6-4d
0.01 0.20 0.03 20.38 2.84
0.25 1.06 0.41 4.23 1.62
0.5 2.20 0.86 4.40 1.73
1.0 5.27 1.92 5.27 1.92
* Calculated assuming a 1:1 redox reaction with the arylamine
tris(pentafluorphenyl)borane (δ: -135.73, -154.66, -163.15
)
In Toluene TFA STd.esp
-135 -140 -145 -150 -155 -160 -165Chemical Shift (ppm)
0.0005
0.0010
0.0015
0.0020
0.0025
0.0030
0.0035
0.0040
0.0045
0.0050
0.0055
0.0060
0.0065
0.0070
Norm
aliz
ed Inte
nsity
Figure S6-1: 19F NMR of tris(pentafluorophenyl)borane in Toluene-d8.
NMR Spectra of 6-1 with 1mol% BCF 19F NMR, 25 °C
B
F
F
F
F
F
F
F
F
F
F
F
F
F
F
F
186
186
rxn 11
-135 -140 -145 -150 -155 -160 -165Chemical Shift (ppm)
0
0.00005
0.00010
0.00015
Norm
aliz
ed I
nte
nsity
Figure S6-2: 19F NMR at 25 °C of compound 6-1 with 1 mol% tris(pentafluorophenyl)borane
in toluene-d8
1H NMR, 25 0C
proton
8 7 6 5 4 3 2 1 0Chemical Shift (ppm)
0.01
0.02
0.03
0.04
0.05
0.06
0.07
0.08
0.09
0.10
0.11
0.12
0.13
0.14
0.15
0.16
Norm
aliz
ed Inte
nsity
0.4
0
Figure S6-3: 1H NMR at 25 °C of compound 6-1 with 1 mol% tris(pentafluorophenyl)borane in toluene-
d8
187
187
NMR Spectra of 6-4d with 1mol% BCF 19F NMR, 25 0C
f19
-135 -140 -145 -150 -155 -160 -165 -170Chemical Shift (ppm)
-0.00005
0
0.00005
0.00010N
orm
aliz
ed
In
ten
sity
Figure S6-4: 19F NMR at 25 °C of compound 6-4d with 1 mol% tris(pentafluorophenyl)borane in
toluene-d8
188
188
1H NMR, 25 0C proton
8.0 7.5 7.0 6.5 6.0 5.5 5.0 4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5Chemical Shift (ppm)
0.01
0.02
0.03
0.04
0.05
0.06
0.07
0.08
0.09
0.10
0.11
0.12
0.13
0.14
0.15
0.16
Norm
aliz
ed Inte
nsity
0.4
0
Figure S6-5: 1H NMR at 25 °C of compound 6-4d with 1 mol% tris(pentafluorophenyl)borane in
toluene-d8
Compound 6-1 and BCF at 1 to 1 molar mixture 19F NMR at 250C in C6D6:
19f rt
-135 -140 -145 -150 -155 -160 -165Chemical Shift (ppm)
0
0.0005
0.0010
0.0015
0.0020
0.0025
No
rma
lize
d I
nte
nsity
-16
4.1
4
-15
7.1
5
-13
5.7
0-1
35
.10
Figure S6-6: 19F NMR at 25 °C of compound 6-1 with 1 mol% tris(pentafluorophenyl)borane
in benzene-d6
189
189
Compound 6-4d and BCF at 1 to 1 molar mixture 19 f benzene.esp
-135 -140 -145 -150 -155 -160 -165Chemical Shift (ppm)
0
0.0005
0.0010
0.0015
No
rma
lize
d In
ten
sity
-16
4.0
4
-15
9.9
1
-15
6.6
1
-13
5.6
8-1
35
.25
Figure S6-7: 19F NMR at 25 °C of compound 6-4d with 1 mol tris(pentafluorophenyl)borane in
benzene-d6
12.5 Additional Information for Chapter 7
12.5.1 Experimental Information
Time of flight transients were acquired by applying a specific electric field across the two
electrodes with a positive potential on the electrode with the charge generation layer (CGL).
Photogeneration was achieved by exposing the CGL to a 10 ns laser pulse through the device
from a dye laser. The device was terminated at resistor of value R and the voltage over time was
recorded on an oscilloscope. Before each test, the capacitance of the cells was measured by three
terminal measurement and a value of R was chosen to ensure that the transit time (tt) was less
than 10 times the RC time constant. Transit times were obtained by fitting moving average lines
to the flat regions of the voltage trace in order to obtain an intersection where the voltage begins
to rapidly drop. The mobility value was calculated using:
190
190
(1)
where µ is the charge carrier mobility, L is the thickness of the device, E is the electric applied
across the device and tt is the transit time calculated as described above. Variable temperature
measurements were achieved by placing the assembled cell into an oven equipped with a glass
window. For each temperature setting, the cell was allowed to equilibrate for 30 minutes before
measurements.
The solid samples were prepared first by mixing 250 mg of 2TIPS, 250 mg of polystyrene, and 7
g of spectro grade dichloromethane. The resulting lacquer was blade coated onto the CGL and
dried at 120 °C for 30 minutes. Film thicknesses were measured using a contact profilometer.
The cell was completed by sandwiching the coated CGL and a counter electrode together at a
pressure greater than 1 MPa.
The polystyrene used was obtained as commercial beads with Mw ~ 350,000 and Mn ~170,000
and a Tg of 95 °C. Prior to use, the beads were dissolved into methylene chloride and precipitated
into methanol followed by drying.
The neat liquid samples were prepared by first modifying the CGL with a 275 nm layer of N,N`-
diphenyl-N,N`-bis(3-methylphenyl)-(1,1`-biphenyl)-4,4`-diamine or TPD by physical vapour
deposition. The layer was deposited at a base pressure of <1 x10-5 Torr at a rate of 10 Å/s. The
cell was then assembled by placing two strips of polyimide film with a gap of ~0.5 cm between
them and a counter electrode strip across the entire layer. Care was taken to avoid direct physical
contact between the two electrodes. The cell was gently clipped together between two
microscope slides using office paper clips and the liquid organic semiconductor was introduced
at the edge of the open cell. Capillary filling of the cell was encouraged by heating the cell to
50°C for several minutes and the filled cells were allowed to cool before measurements began.
Synthesis of N-(2-ethylhexyl)carbazole: Carbazole (2g, 11.96 mmol), 2-ethylhexylbromide
(3.46 g, 17.94 mmol), sodium hydroxide (0.717 g, 17.94 mmol), tetrabutylammonium bromide
(100 mg, 0.120 mmol), and acetone (10 mL) were reacted at reflux for 48 hours. After cooling,
the reaction was filtered and the eluent was first purified by column chromatography (10:1
Hexanes/Toluene) over silica gel and then by vacuum distillation. The final product was isolated
191
191
as a clear oil (2.186 g, 7.822 mmol). 1H NMR (400 MHz, C6D6): δ 8.07 (dq, J1 = 7.80 Hz, J2
=0.65 Hz, 2H) 7.44 (tt, J1 = 7.80 Hz, J2 = 1.36 Hz, 2H), 7.29 (dt, J1 = 8.19 Hz, J2 = 0.78 Hz, 2H),
7.24 (tt, J1 = 8.19 Hz, J2 = 0.78 Hz, 2H), 3.77 (dd, J1 = 7.41 Hz, J2 = 2.14 Hz, 2H), 1.93 (m, 1H),
1.11 (m, 8H), 0.77 (t, J = 7.02 Hz, 3H), 0.68 (t, J = 7.02 Hz, 3H). 13C NMR (100 MHz, C6D6): δ
141.7, 126.2, 123.9, 121.2, 119.6, 109.6, 47.7, 39.8, 31.6, 29.3, 25.0, 23.6, 14.5, 11.3.
12.5.2 Supplemental Information for Chapter 7
Hole Mobilities of 2TIPS in Polystyrene (50 wt%) at Multiple Thicknesses
1.00E-06
1.00E-05
300 400 500 600 700 800 900
Ho
le M
ob
ilit
y (
cm
2v
-1s
-1)
E1/2 (V/cm)1/2
37 um Film 9 um Film 5 um Film
Figure S7-1: Extracted hole mobilities of 2TIPS in a polystyrene matrix (50 wt%) with different
film thicknesses.
Hole Mobilities in Neat 2TIPS using Multiple Thicknesses
192
192
1.00E-05
1.00E-04
150 200 250 300 350
Mo
bilit
y (
cm
2/V
s)
E1/2 (V/cm)1/2
125 um spacer
50 um spacer
75um
Figure S7-2: Extracted hole mobilities of neat 2TIPS using different sample thicknesses.
Example Transient of transport through N-(2-ethylhexyl)carbazole
1.50E-03
1.50E-02
1.50E-03 1.50E-02 1.50E-01
vo
ltag
e (
V)
time (s)
ttransit
Figure S7-3: An example of a time of flight transient obtained through neat N-(2-
ethylhexyl)carbazole.
193
193
Hole Mobility of N-(2-ethylhexyl)carbazole
1.00E-07
1.00E-06
1.00E-05
1.00E-04
260 270 280 290 300 310 320
Ho
le M
ob
ilit
y (
cm
2/V
s)
E1/2 (V/cm)1/2
Figure S7-4: Hole mobilities of neat N-(2-ethylhexyl)carbazole
194
194
12.6 Additional Information for Chapter 8
65011501650215026503150
Tra
nsm
itta
nc
e
Wavenumber (cm-1)
QM4
Si-H
A
B
C
Figure S8-1: Infrared spectra of films A, B, and C prepared in a KBr matrix.
195
195
0
0.2
0.4
0.6
0.8
1
385 435 485 535 585
No
rma
lize
d P
L I
nte
ns
ity
Wavelength (nm)
B C E
Figure S8-2: Solid-state photoluminescence of films B, C, and E. Excitation wavelength 365
nm.
196
196
-0.1 0.1 0.3 0.5 0.7 0.9 1.1 1.3
Cu
rre
nt
(a.u
.)
Voltage (vs. Ag/AgCl) Fi
Figure S8-3: Electrochemistry of D on ITO in water with 0.1M NaCl as the supporting
electrolyte. (black) Cyclic voltammetry, (red) Differential pulse voltammetry.
197
197
12.7 Additional Information for Chapter 10
11.7.1 Experimental Information
General methods and procedures
Chemicals were purchased and used without further purification using standard laboratory
methods. NMR spectra were collected at 25 °C at a field strength of 400 MHz. Chemical shifts
are referenced to residual solvent signals. High resolution mass spectroscopy (HRMS) was
obtained using an AccuTOF mass spectrometer (JEOL USA Inc., Peabody, MA) with a DART-
SVP ion source (Ionsense Inc., Saugus, MA) using He gas. Electrochemistry was performed
using a standard three electrode setup. A platinum disk was used as the working electrode while
a platinum wire was used as a counter electrode. All data is corrected to the internal redox
standard of decamethylferrocene and numbers are referenced to Ag/AgCl. Thermogravimetric
analysis (TGA) was performed at ramp rate of 10 °C/min under N2.
Density functional theory calculations were performed using Spartan ’06 for windows. Geometry
optimizations were carried out using the Becke–Lee–Yang–Parr exchange correlation function
with a 6-31G(D) basis set. The OLEDs were fabricated in a cluster tool (Kurt J. Lesker
LUMINOS) under a base pressure of <10-8 Torr on pre-patterned indium tin oxide (ITO) coated
glass with a thickness of 1.1 mm. Prior to loading, the ITO was cleaned using standard solvents.
Subsequently, a MoO3 layer was deposited on top to obtain a high work function and facilitate
hole injection into CBP. All organic layers were deposited in a dedicated chamber, whereas the
cathode, consisting of LiF(1 nm)/Al(100 nm), was evaporated in a separate chamber without
breaking vacuum. The active area of each device was 2 mm2 as measured by an optical
microscope. The EQE and power efficiency were measured using an integrating sphere with a
silicon photodiode with NIST traceable calibration. The electroluminance (EL) spectra were
measured using an Ocean Optics USB4000 spectrometer. All measurements were done in air
with 3 s dwell time between each data point.
Synthesis of 9-1 and 9-2
Synthesis of 9-1: Tetrachlorophthalonitrile (1.00 g, 3.76 mmol), catechol (1.03 g, 9.38 mmol),
potassium carbonate (1.30 g, 9.38 mmol), and dimethylformamide (20 mL) were heated to 100
°C under argon for 1 h. After cooling to room temperature, the solids were filtered and washed
198
198
with water (100 mL) then methanol (50 mL). The collected solids were dried under vacuum to
yield a fine white powder (1.20 g, 94% yield). 1H NMR (400 MHz, CDCl3): δ 7.08–7.01
(m). HRMS (DART) [M+NH4] calcd for C20H12N3O4 358.0828, found 358.0822. Elemental
Analysis calcd for (%) C20H8N2O4: C 70.59, H 2.37, N 8.23. Found: C 70.56, H 2.33, N 8.31.
Synthesis of 9-2: Tetrachlorophthalonitrile (3.00 g, 11.3 mmol), 2,3-dihydroxynaphthalene (4.52
g, 28.2 mmol), potassium carbonate (3.90 g, 28.2 mmol), and dimethylformamide (60 mL) were
heated to 100 °C under argon for 5 h. The cooled solids were collected by filtration and washed
with water (200 mL), methanol (200 mL), then dichloromethane (50 mL), in that order. The
resulting solids were dried under vacuum to yield a fine white powder (4.74 g, 95% yield). 1H
NMR (400 MHz, CDCl3): δ 7.74 (q, J = 3.52 Hz, 4H), 7.51 (d, J = 7.91 Hz, 4H), 7.45 (q, J =
3.22 Hz, 4H). HRMS (DART) [M+H] calcd for C28H13N2O4 441.0875, found 441.0876.
Elemental Analysis calcd for (%) C28H12N2O4: C 76.36, H 2.75, N 6.36. Found: C 75.98, H 3.00,
N 6.29.
References
1. I. Noviandri, K.N. Brown, D.S. Fleming, P.T. Gulyas, P.A. Lay, A.F. Masters, P.
Leonidas, J. Phys. Chem. B 103 (1999) 6713–6722.
2. A.D. Becke, Phys. Rev. A 38 (1988) 3098–3100.
199
199
12.8 Appendices References for Chapter 10
12.8.1 General Information
Starting materials and solvents were purchased from various companies and used without further
purification.
NMR Spectra were collected at 25 °C at a field-strength of 400 MHz. In order to resolve the
isomers of compound 2, NMR spectra at a field strength of 700 MHz was collected. All 1H and 13C spectra are referenced to residual solvent or TMS and chemical shifts are reported in parts
per million while coupling constants are reported in Hz. 19F and 11B NMR are referenced to BF3-
OEt2 which we arbitrarily assigned to 0 ppm for both nuclei. External standards were used with
each NMR experiment.
High resolution mass spectroscopy (HRMS) was acquired with either DART or ESI ionization
techniques. For those using DART, the spectra were acquired using an AccuTOF mass
spectrometer (JEOL USA Inc. Peabody, MA) with a DART-SVP ion source (Ionsense Inc.,
Saugus, MA) using He Gas.
Electrochemistry was performed in a solution of DCM with 0.1 M tetraammonium perchlorate as
a supporting electrolyte. A 1 mm platinum disc was used as a working electrode with a platinum
wire counter electrode and Ag/AgCl reference electrode. All cyclic voltammetry experiments
were run with an internal standard of decamethylferrocene at a scanning rate of 100 mV/s. All
half wave potentials are corrected to the published halfwave potential of decamethylferrocene (-
0.012 V vs. Ag/AgCl).2 All half wave potentials are reported relative to Ag/AgCl.
Density functional theory (DFT) calculations were implemented using Spartan ’06 for windows. Structures were geometry optimized using the Becke-Lee-Yang-Parr exchange correlation function3 with a 6-31G(D) basis set.
2 Noviandri, I.; Brown, K.N.; Fleming, D.S.; Gulyas, P.T.; Lay, P.A.; Masters, A.F.; Leonidas, P. J. Phys. Chem. B
1999, 103 (32), 6713-6722. 3 Becke, A.D. Phys. Rev. A 1988, 38 (6), 3098-3100
200
200
12.8.2 Synthetic Details and Compounds Characterization
Compound 10-2
Tetrachlorophthalonitrile (1.000 g, 3.76 mmol), 3,5-di-t-butylcatechol (1.755 g, 7.90 mmol),
potassium carbonate (1.091 g, 7.90 g), and N,N-dimethylformamide (20 mL) were heated to 100
°C for 6 hours under an atmosphere of argon gas. Upon cooling, water (20 mL) was added to the
solution to form a fine slurry. The solids were collected by filtration, washing with water (3 x 50
mL) and methanol (3 x 50 mL) resulting in the pure product as a fine white powder (1.927 g,
91% Yield). HRMS (DART) [M+H] cald for C36H41N2O4 565.30663, found 565.30659.
Compound 10-3a
Compound 10-1 (11.690 g, 34.4 mmol) was dissolved in 1,2-dichlorobenzene (300 mL) under an
inert atmosphere. Boron trichloride (81 mL of a 1M solution in heptanes, 81 mmol) was added to
this solution and the heptanes were distilled off and the mixture was refluxed for 2 hours. Upon
cooling, the dichlorobenzene was removed under vacuum and the resulting black solids were
continuously extracted with methanol (48 Hrs) then acetonitrile (24 Hrs) using a soxhlet
apparatus. The remaining solids were dried under vacuum resulting in a fine green/black powder
assumed to be the chloro substituted subphthalocyanine product (8.01 g, 66 % crude yield).
The crude -Cl substituted subphthalocyanine (500 mg, ~0.47 mmol), 4-t-butylphenol (352 mg,
2.34 mmol), and chlorobenzene (5 mL) were heated at reflux for 48 hours. Upon cooling, the
chlorobenzene was removed under vacuum and the resulting green solids were loaded onto a
plug of alumina (basic, standard activity) and extracted continuously with dichloromethane using
a Kaufman apparatus. The extracted, dark green liquor was then concentrated under vacuum
resulting in a dark green powder (319 mg, 58 % Yield). HRMS (ESI) [M+] calcd 1180.2506,
found 1180.2770. 1H (400 MHz, CD2Cl2): δ 7.21 (d, J = 7.8 Hz, 6 H), 6.96-6.79 (m, 20H), 5.47
(d, J = 8.6 Hz, 2H), 1.06 (s, 9H). 11B (CD2Cl2): δ -14.8
Compound 10-3b
Using the procedure for 10-3a: The crude Cl substituted subphthalocyanine (500 mg, ~0.47
mmol), pentafluorophenol (431 mg, 2.34 mmol), and chlorobenzene (5 mL) were heated at
reflux for 18 hours. The product was isolated as a dark green powder (207 mg, 36 % yield). MS
201
201
(ESI) [M+] calcd 1215.1, found 1215.1. MS signal insufficient for high resolution mass
spectroscopy. 1H (400 MHz, CD2Cl2): δ 7.29 (dd, J1 = 8.0 Hz, J2 = 1.4 Hz, 6 H), 7.16-7.00 (m,
20H). 19F (CD2Cl2, referenced to BF3-O(Et)2): δ -5.35 (d, J = 20.6 Hz, 2F), -10.3 (t, J = 20.6 Hz,
2F), -11.7 (t, J = 20.6 Hz, 1F). 11B (CD2Cl2, referenced to BF3-O(Et)2): δ -14.5
Compound 10-4a
10-2 (2.258 g, 4.00 mmol), phthalonitrile (256 mg, 2 mmol), 20 mL 1,2-dichlorobenzene were
stirred under an inert atmosphere. Boron trichloride (10 mmol, 10 mL of heptanes solution) was
added to the mixture and the heptanes were distilled off were reacted for 2 hours under and inert
atmosphere. Upon cooling, the solution was dried under vacuum and the blue solids were
continuously extracted with methanol for 18 hours. The remaining solids resembled a dark blue
powder (1.554 g, 90% crude yield).
The crude above product (1.000 g, ~1.15 mmol), pentafluorophenol (1.000 g, 5.43 mmol), and
chlorobenzene (10 mL) were refluxed under an inert atmosphere for 18 hours. After removal of
the chlorobenzene under vacuum, the remaining blue solids were purified by column
chromatography over silica gel eluting with 3/2 hexanes/toluene. A fraction containing a single
blue spot was isolated (258 mg, 22% Yield) and shown to be a single product on low molecular
weight GPC. HRMS (DART) [M+H] calcd for C58H48BF5N6O5 1015.3778, found 1015.3718. 1H
(400 MHz, CDCl3): δ 8.80 (dm, J1 = 20.7 Hz, 4H), 7.91 (q, J = 3.1 Hz, 4H), 7.15 (d, J = 2.3 Hz,
1.7H), 7.07-7.05 (m, 2H), 6.95 (d, J = 2.3 Hz, 0.3H), 1.94 (s, 15.1H), 1.46 (s, 2.9), 1.36 (s, 15.1),
1.29 (s, 2.9). 11B (CDCl3, referenced to BF3-O(Et)2): δ -14.6. 19F (CDCl3, referenced to BF3-
O(Et)2): δ -5.3 (d, J = 21.4 Hz, 2F), -11.1 (t, J = 21.4 Hz, 2F), -12.0 (t, J = 21.4 Hz, 1F).
Compound 10-4b
Compound 10-2 (4.00 mmol, 2.258 g) tetrafluorophthalonitrile (4.00 mmol, 800 mg), 20 mL 1,2-
dichlorobenzene, and BCl3 (10.0 mmol, 10 mL of a 1M solution in heptanes) were mixed
together under argon. The heptanes were then distilled off and the reagents heated at reflux for 2
hours. After cooling the solvent was removed under vacuum and the dark green/blue solids were
continuously extracted with methanol using a soxhlet apparatus for 16 hours. The extracted
solids were dried and the crude, -Cl substituted product collected (1.511 g, 75% crude yield).
202
202
The above crude product (800 mg, ~0.790 mmol), pentafluorophenol (800 mg, 4.35 mmol), and
chlorobenzene (8 mL) were refluxed under argon for 10 hours. After removal of the solvent, the
solids were purified by flash chromatography over silicon eluting with 5/1 hexanes to toluene.
Two green fractions with identical retention times by lmw GPC and UV-VIS absorbance spectra
were isolated (fraction 1: 113 mg, 12% Yield, fraction 2: 107 mg, 12% yield). Unfortunately, the
second fraction quickly degraded upon heating under vacuum and only the first fraction was
characterized. HRMS (DART) [M+] calcd for C58H40BF13N6O5 1155.3060, found 1158.2968. 1H
(400 MHz, CDCl3): δ 7.18 (2.3 Hz, 2H), 7.08 (2,3 Hz, 2H), 1.83 (s, 18H), 1.37 (s, 18H). 11B
(CDCl3, referenced to BF3-O(Et)2): δ -14.8. 19F (CDCl3, referenced to BF3-O(Et)2): δ 17.6 (t, J =
18.3 Hz, 2F), 14.9 (t, J = 18.3 Hz, 2F), 4.3 (t, 18.3 Hz, 2F), 3.4 (t, J = 18.3 Hz, 2F), -5.5 (2, J =
22.9 Hz, 2F), -9.9 (t, J =20.6 Hz, 2F), -10.3 (t, J = 22.9 Hz, 1F)
Compound 10-4c
Compound 10-2 (4.00 mmol, 2.258 g) tetrachlorophthalonitrile (4.00 mmol, 1.063 g), 20 mL 1,2-
dichlorobenzene, and BCl3 (10 mmol, 10 mL of a 1M solution in heptanes) were mixed together
under argon. The heptanes were then distilled off and the reagents heated at reflux for 2 hours.
After cooling, the solvent was removed under vacuum and the dark green/blue solids were
continuously extracted with methanol using a soxhlet apparatus for 16 hours. After extraction,
the solids were dried and the crude, -Cl substituted product collected (652 g, 29% crude yield).
The above crude product (500 mg, ~0.438 mmol), pentafluorophenol (500 mg, 2.72 mmol), and
chlorobenzene (5 mL) were refluxed under argon for 18 hours. After drying, the resulting dark
blue/green powder was purified twice successively over silica gel eluting with a gradient from
10/1 to 3/1 Hexanes/Toluene. HRMS (DART) [M+H] calcd for C58H40BCl8F5N6O5 1287.0660,
found 1287.0719. 1H (400 MHz, CDCl3): δ 7.22-7.19 (m, 1.9H), 7.14 (d, J = 2.3 Hz, 0.8H), 7.10
(d, J = 2.3 Hz, 0.8H), 6.95 (d, J = 2.3 Hz, 0.5H), 1.83 (s, 12H), 1.55 (s, 5.0H), 1.40-1.38 (m,
19H). 11B (43 MHz, CDCl3, referenced to BF3-O(Et)2): δ -14.7. 19F (376 MHz, CDCl3, referenced
to BF3-O(Et)2): δ -5.4 (m, 2F), -9.9 (m, 2F), -10.6 (m, 1F).
12.8.3 NMR Study of Phthalonitrile 10-2
Due to the nature of the substitution reaction, the following three isomers are expected:
203
203
Figure S10-1: Structures of three expected isomers for compound 10-2
HPLC analysis was not able to isolate and quantify the ratios of each isomer. 1H NMR at 400
MHz showed some separation of the aromatic protons for each isomer but the resolution was
insufficient. To resolve these peaks, 1H NMR and gCOSY (1H-1H) analysis was performed at
700 MHz (Figures S2-4). The enhanced resolution afforded by the higher field strength allowed
enough resolution for accurate integration of a number of peaks. Through ring coupling detected
by gCOSY and knowledge of the integration values in the 1D spectrum allowed for
quantification of each isomer.
204
204
cdcl3 proton 700 mhz
7.0 6.5 6.0 5.5 5.0 4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5 0Chemical Shift (ppm)
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
No
rma
lize
d In
ten
sity
0.0
0
7.2
6
Figure S10-2: 1H NMR spectrum at 700 MHz in CDCl3 of compound 10-2. Inset: Close up of
alkyl region of spectrum.
cdcl3 proton 700 mhz
7.05 7.00 6.95 6.90 6.85 6.80Chemical Shift (ppm)
0.01
0.02
0.03
0.04
0.05
0.06
0.07
0.08
0.09
0.10
0.11
0.12
0.13
Norm
alized Inte
nsity
Figure S10-3: Zoom of aromatic region of 1H NMR spectrum at 700 MHz in CDCl3 of
compound 10-2. Coloured lines show coupled spin systems from gCOSY experiment.
cdcl3 proton 700 mhz
1.50 1.45 1.40 1.35 1.30 1.25Chemical Shift (ppm)
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
Norm
aliz
ed I
nte
nsity
205
205
7.05 7.00 6.95 6.90 6.85 6.80 6.75F2 Chemical Shift (ppm)
6.75
6.80
6.85
6.90
6.95
7.00
7.05
F1
Ch
em
ica
l S
hift
(pp
m)
Figure S10-4: gCOSY (1H, 1H) spectrum at 700 MHz in CDCl3 of compound 10-2.
1H NMR (700 MHz, CDCl3): δ 7.07-7.05 (m, 4.1 H ), 7.05 (d, J = 2.4 Hz, 1.6 H), 7.03 (d, J = 2.4
Hz, 1 H), 6.96 (d, J = 2.4 Hz, 2.6 H), 6.93 (d, J = 2.4 Hz, 1.6 H), 6.91 (d, J = 2.4 Hz, 1 H), 6.79
(d, J = 2.4 Hz, 1.6 H), 1.48-1.45 (m, 61 H), 1.31-1.29 (m, 61 H).
12.8.4 UV-Vis and PL Plots
0
0.2
0.4
0.6
0.8
1
0
20000
40000
60000
80000
100000
300 400 500 600 700 800 900
Ph
oto
lum
ine
sce
nt
Inte
ns
ity
(a.u
.)
Ex
tin
cti
on
Co
eff
icie
nt
(L-1
mo
l-1c
m-1
)
Wavelength (nm)
206
206
Figure S10-5: UV-VIS absorbance spectrum of compound 10-3a in THF (left axis) and
photoluminescence emission spectrum of 10-3a in THF at an excitation wavelength of 650 nm.
0
0.2
0.4
0.6
0.8
1
0
10000
20000
30000
40000
50000
60000
70000
80000
90000
300 400 500 600 700 800 900
Ph
oto
lum
ine
sce
nt
Inte
ns
ity
(a.u
.)
Ex
tin
cti
on
Co
eff
icie
nt
(L-1
mo
l-1c
m-1
)
Wavelength (nm)
Figure S10-6: UV-VIS absorbance spectrum of compound 10-3b in THF (left axis) and
photoluminescence emission spectrum of 10-3b in THF at an excitation wavelength of 650 nm.
0
0.2
0.4
0.6
0.8
1
0
10000
20000
30000
40000
50000
60000
300 400 500 600 700 800
Ph
oto
lum
ine
sce
nt
Inte
ns
ity
(a.u
.)
Ex
tin
cti
on
Co
eff
icie
nt
(L-1
mo
l-1c
m-1
)
Wavelength (nm)
Figure S10-7: UV-VIS absorbance spectrum of compound 10-4a in THF (left axis) and
photoluminescence emission spectrum of 10-4a in THF at an excitation wavelength of 601 nm.
207
207
0
0.2
0.4
0.6
0.8
1
0
5000
10000
15000
20000
25000
30000
35000
40000
45000
300 400 500 600 700 800 900
Ph
oto
lum
ine
sce
nt
Inte
ns
ity
(a.u
.)
Ex
tin
cti
on
Co
eff
icie
nt
(L-1
mo
l-1c
m-1
)
Wavelength (nm)
Figure S10-8: UV-VIS absorbance spectrum of compound 10-4b in THF (left axis) and
photoluminescence emission spectrum of 10-4b in THF at an excitation wavelength of 621 nm.
0
0.2
0.4
0.6
0.8
1
0
10000
20000
30000
40000
50000
300 400 500 600 700 800 900
Ph
oto
lum
ine
sce
nt
Inte
nsit
y (
a.u
.)
Ex
tin
cti
on
Co
eff
icie
nt
(L-1
mo
l-1cm
-1)
Wavelength (nm)
Figure S10-9: UV-VIS absorbance spectrum of compound 10-4c in THF (left axis) and
photoluminescence emission spectrum of 10-4c in THF at an excitation wavelength of 626 nm.
208
208
0
10000
20000
30000
40000
50000
60000
70000
80000
90000
300 350 400 450 500 550 600 650
Ex
tin
cti
on
Co
eff
icie
nt
(L-1
mo
l-1c
m-1
)
Wavelength (nm)
Figure S10-10: UV-VIS absorbance spectrum of compound F5-BsubPc in THF.
209
209
12.9 DFT Calculated Molecular Orbitals
N
N
N
NN N
B
O
O
OO
O
O O
O
OO
O
O
O
HOMO LUMO
Figure S10-11: Geometry optimized DFT structures for compound 10-3a showing HOMO and
LUMO distributions.
210
210
HOMO LUMO
Figure S10-12: Geometry optimized DFT structures for compound 10-3b showing HOMO and
LUMO distributions.
211
211
HOMO LUMO
Figure S10-13: Geometry optimized DFT structures for one isomer of compound 10-4a with
HOMO and LUMO distributions.
212
212
HOMO LUMO
Figure S10-14: Geometry optimized DFT structures for one isomer of compound 10-4b with
HOMO and LUMO distributions.
213
213
HOMO LUMO
Figure S10-15: Geometry optimized DFT structures for one isomer of compound 10-4c with
HOMO and LUMO distributions.
214
214
12.10 Cyclic Voltammetry
-2 -1.5 -1 -0.5 0 0.5 1 1.5
Voltage (V)
E1/2ox
E1/2red1
E1/2reference
Figure S10-16: Cyclic voltammogram of compound 10-3a in DCM with 0.1M
tetrabutylammonium perchlorate and decamethylferrocene as an internal standard.
-1.5 -1 -0.5 0 0.5 1 1.5
Voltage (V)
E1/2ox
E1/2red1
E1/2reference
Figure S10-17: Cyclic voltammogram of compound 10-3b in DCM with 0.1M
tetrabutylammonium perchlorate and decamethylferrocene as an internal standard.
215
215
-1.5 -1 -0.5 0 0.5 1 1.5
Voltage (V)
E1/2ox
E1/2red
E1/2reference
Figure S10-18: Cyclic voltammogram of compound 10-4a in DCM with 0.1M
tetrabutylammonium perchlorate and decamethylferrocene as an internal standard.
-2 -1.5 -1 -0.5 0 0.5 1 1.5 2
Voltage (V)
E1/2ox
E1/2red1
E1/2red2
E1/2reference
Figure S10-19: Cyclic voltammogram of compound 10-4b in DCM with 0.1M
tetrabutylammonium perchlorate and decamethylferrocene as an internal standard.
216
216
-2 -1.5 -1 -0.5 0 0.5 1 1.5 2
Voltage (V)
E1/2ox
E1/2red1
E1/2red2
E1/2reference
Figure S10-20: Cyclic voltammogram of compound 10-4c in DCM with 0.1M
tetrabutylammonium perchlorate and decamethylferrocene as an internal standard.