university of groningen control of translational and

University of Groningen

Control of translational and rotational movement at nanoscaleStacko, Peter

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Molecular dragsters: Towards controlled translational motion on surfaces

| 41

Chapter II:

Molecular dragsters: Towards controlled

translational motion on surfaces

Molecular dragsters bearing two appending molecular motor units as the

propelling wheels have been synthesized. The two dragsters feature different

sizes of the rotor units. The motors preserve their rotary function in solution and

preliminary experiments regarding movement on a surface under ambient

conditions have been performed.


42 |

Introduction

Directional motion of molecules offers prospects for development of unique and

unprecedented nanotechnology devices rivaling machinery developed by

Nature1,2 such as motor proteins moving along microtubules3, the ATPase rotary

motion4,5 or myosin V walking on actin filaments6,7. Examples of directional

motion in the literature include DNA walkers8,9, photochemically10,11 and redox-

driven12 motors and catenane, and rotaxane translational systems, although the

systems are predominantly studied in solution.13–17

Regarding surface confined motors, directional movement can be divided to

rotary or translational motion. Achieving rotary motion is the more

straightforward option as the two major conditions to be fulfilled are anchoring

the molecules on the surface18–22 and the surface should not interfere with

process of controlling the motion; such as quenching of the excited state for

photochemically driven molecules, or redox reaction between the molecules and

surface for electrochemically driven processes.

On the other hand, there are many obstacles associated with autonomous

directional translational movement on surfaces. For example, the attractive

forces between the molecules and the surface have to be strong enough to

facilitate physisorption of molecules on the surface, while at the same time, the

forces have to be weak enough to allow for propulsion along the surface upon

application of stimuli. Perhaps due to the delicate balance necessary to achieve

this goal, autonomous directional movement of molecules on surface constitutes

a major challenge in contemporary chemistry.

Though, several examples of directional translational movement of molecules;

such as fullerenes23, porphyrins24, cyclodextrins25 or molecular landers26, on

surfaces can be found in the literature, however, the majority of them is induced

by “pushing” or “pulling” of the molecules with an STM tip (e.g. non-

autonomous).27,28 In addition, most of the observed motion is attributed to

sliding or slipping motion, rather than rolling motion and the exceptions to

these observations will be discussed here.

In a simple example, Grill et. al. have demonstrated that a molecule consisting of

two triptycene units connected with an axle (Figure 1a) can exhibit translational

movement when adsorbed on a Cu (110) surface at 25 K.28 Placing the STM tip


| 43

on top of the molecule and moving it perpendicular to the axle of the molecules,

4 nm translational movement was observed (Figure 1b-d).

Figure 1. (a) Two triptycene units connected with an axle. (b) Scheme of manipulation with the STM tip. (c) STM image of the molecule on Cu (110) prior to manipulation. d) STM image of the molecule after the manipulation. (reproduced from ref. 24)

The group of Tour was able to demonstrate the wheel-assisted rolling motion on

gold surface at single molecular level using STM.29–31 For this purpose, the

nanocar 2.1 with four wheels as well as the three-wheel analogue 2.1 has been

synthesized (Figure 2). The comparison of movement for the two molecules

provided the evidence for wheel-assisted rolling motion. Upon heating the Au

surface to 200 °C only the four-wheel nanocar 2.1 showed translational motion

perpendicular to the axes, whereas the analogue 2.1 displayed pivoting motion

(Figure 3). This behavior demonstrates the expected fullerene-facilitated rolling

which is contrast to most examples in the literature where simple pushing is

almost universally accepted as the mechanism for large molecules.32–34


44 |

Figure 2. The structure of nanocar 2.1 (left) and the three-wheel analogue 2.2 (right); (Figure reproduced from ref. 25) In addition, both pushing and pulling movement induced by the STM tip was examined on these molecules. Slightly curved, however preferentially linear movement was clearly observed (Figure 3). This movement could not be reproduced when the tip was positioned on the side of the molecule instead of behind the molecules.

Figure 3. (left) Nanocar 2.1 rolling on Au surface. (a-e). A small section of a sequence of images taken during annealing at ~200 °C (Vb = -0.95 V, It = 200 pA; image size is 51 × 23 nm2). The orientation of 2.1 is determined easily by the fullerene wheel separation, with motion occurring perpendicular to the axles. The acquisition time for each image is

2.1 2.2


| 45

approximately 1 min, with a-e selected from a series spanning 10 min, which shows 80° pivot (a) followed by translation interrupted by small-angle pivot perturbations (b-e). (right) Structure and pivot motion of the trimers. (a) Structure of trimers. A sequence of STM images (b-e) acquired approximately 1 min apart during annealing at ~225 °C show the pivoting motion of 2.2 (both circled molecules) and lack of translation in b-e of any molecules. (Vb = -0.7 V, It ) 200 pA; image size is 34 × 27 nm2). Monatomic step edges in these images are lined with clustered molecules. (f) A summary of the two methods of motion for the different structures showing that nanocar 2.1 consecutively pivots and then translates perpendicular to its axles, whereas trimer 2.2 pivots but does not translate on the surface. For clarity, both structures are drawn devoid of the alkoxy units (reproduced from ref. 27).

Another attempt from group of Tour and co-workers to construct a “motorized

nanocar”, rather than a car being pushed or pulled by STM tip contained

p-carborane as a wheel and a light-driven molecular motor as the engine of the

nanocar 2.3.35,36 The molecule was thought to be propelled by the molecular

motor along the substrate surface as it can perform repetitive unidirectional

rotary motion induced by light (Figure 4). The molecule has only been studied

by 1H NMR and UV-vis spectroscopy in the solution and unfortunately, no

reports of movement on surface studied by STM have been made. The function

of the molecular motor was preserved in the presence of p-carborane units

unlike in the case of fullerene-C60 wheels.29

Figure 4. (left) The structure of the nanocar 2.3 with p-carborane units as wheels and molecular motor in the middle. (right) Irradiation (a) of the motor unit leads to rotation of the motor (b) inducing the forward translational motion (c-d). (Reproduced from ref. 25)

Perhaps the most successful demonstration of unidirectional movement on a

surface has been reported by the group of Feringa.37 The molecular nanocar 2.4

features a chassis connected to four molecular motors designated to propel the

molecule along the surface when performing the rotational movement (Figure

2.3


46 |

5). Upon electronic excitation using an STM tip double bond isomerization

occurs followed by a helix inversion resulting in rotary motion pushing the

molecule forward. A correct configuration of the stereogenic centers was

required as only in the meso isomer both of the motor units rotate in the forward

direction from the external point of view. Ultimately, the molecule was shown to

undergo a preferentially linear movement showing that the intrinsic motor

function is capable of converting external energy input into mechanical action

(Figure 6).

Figure 5. (a) The structure of nanocar 2.4 with embedded four molecular motors as wheels. (b) Schematic representation of the concept (Figure reproduced from ref. 33)

Figure 6. (a) STM image (imaging parameters: area 10.2 nm × 39.3 nm, current I = 74 pA, U = 47 mV) of the initial position. The black area was scanned only after the molecule moved into it. (b) Trajectory depicting the individual steps taken. (c) Final position after ten consecutive voltage pulses. (d) The action spectrum for movement shows a voltage threshold at 500 mV. Each data point represents 8 to 40 manipulations performed on various molecules (I = 30–50 pA). Error bars represent the standard deviation from the probability for successful events. (e) STM frames corresponding to individual steps of the trajectory in (b) excluding starting and final position (reproduced from ref. 33).

2.4


| 47

Design of the dragsters

Some of the initial difficulties in the molecular nanocar project included poor

volatility of the molecule for surface deposition as well as rather high voltage

required for movement of the molecule. Motivated by the success of the

electrically-driven molecular nanocar, we sought to address these issues by

simplifying the design along with enabling modification of the molecule for

future applications such as cargo transport. One could imagine a cargo unit

being attached to the motorized part and once at the desired destination, the

cargo could be released. For this purpose, we envisioned that molecular

dragsters bearing only two rotating motor units (instead of four) could be

sufficient (Figure 7). To first prove that the unidirectionality of the molecular

dragsters on surface is preserved, only a dummy cargo unit, sharing the same

carbazole building block as the other half of the molecule, was attached at this

point. In order to assess the influence of wheel “size” on the unidirectional

movement, we decided to construct two dragsters with different wheel sizes –

one based on simple fluorene units and the second one, larger, based on phenyl

substituted fluorene units.

Figure 7. The design of the molecular dragsters consisting of a motorized part with two motor units and a dummy cargo unit.


48 |

Synthesis of the dragsters and intermediates

Due to similarities in the design, the synthesis of the molecular dragsters is

based on that of the molecular nanocar 2.4, although with several crucial

modifications in both synthetic and purification procedures.37

The synthesis started with the preparation of 2,7-dibromo-9H-carbazole as it is a

common building block for both parts of the molecule (2.11 and 2.18a-b, vide

infra). For this purpose, 4,4’-dibromobiphenyl was nitrated using fuming nitric

acid in glacial acetic acid (Scheme 1).38,39 The resulting mono-nitrated product

2.7 was then subjected to reductive cyclization using PPh3 in o-DCB at high

temperature to facilitate the formation of 2.8 in a good overall yield.40

Scheme 1. Synthesis of 2.8 as the common intermediate for further synthesis.

From this intermediate, both parts of the dragster have been synthesized. The

carbazole 2.8 was reacted with a large excess (4 eq.) of 1,4-diiodobenzene in

Ullmann coupling catalyzed by CuI and 1,10-phenanthroline as a ligand to

provide the N-substituted carbazole 2.9 (Scheme 2).41 The excess of 1,4-

iodobenzene prevented the formation of the di-substituted product as well as

Ullmann coupling between two molecules of the starting material.


| 49

Scheme 2. Synthesis of the unpropelled part 2.11 of the dragsters from the carbazole 2.8.

Following a procedure for Sonogashira coupling with TMSA using Pd(PPh3)Cl2

and CuI as the catalysts, a TMS-protected acetylene was installed onto the

molecule to give compound 2.10. The acetylene would then, upon deprotection,

serve as a connection point with the other half of the molecule. It should be

stressed that excess of TMSA was avoided as it led to coupling at the bromo-

substituted positions even at room temperature. Besides that, a complete

selectivity for the iodo-substituted reaction site was observed. Metal-halogen

exchange at -78 °C using n-BuLi, followed by a substitution of the di-lithiated

carbazole with TMSCl and deprotection of the acetylene in situ with KOH

afforded the final building block 2.11 in 84 % yield over the three steps (Scheme

3).

In the next stage, the motorized part 2.18a-b of the dragster was to be

synthesized. Unlike in the case of the nanocar 2.4 where the solubilizing hexyl

chains were introduced via Sonogashira coupling followed by hydrogenation37,

in this synthesis the alkyl moieties were installed in one step using Pd(dppf)Cl2

catalyzed variation of Kumada coupling in 82% yield (Scheme 3, 2.12).42


50 |

Scheme 3. Synthesis of the diketone 2.14 for double Barton-Kellogg coupling.

Employing the same strategy as for the nanocar, the diketone 2.13 was formed

from the carbazole 2.12 by a Friedel-Crafts-Nazarov cyclization sequence with

methacrylic acid in PPA (Scheme 4).37 Despite the solubilizing chains, the

compound 2.13 is poorly soluble in most organic solvents. Due to this, the

original eluent for flash column chromatography was substituted for

dichloromethane, improving the yield to 39% across multiple steps. Compound

2.13 was isolated as a mixture of the two possible diastereomers (1:1, based on 1H NMR spectroscopy) and used as such throughout the rest of the synthetic

sequence. Both the Kumada coupling and the condensation could be

conveniently carried out on a multigram scale. Reproduction of the procedure

reported for the nanocar 2.4 involving a protection of the carbazole 2.13 with a t-

Boc group followed by a thionation using Lawesson’s reagent was unfortunately

not met with a success due to constant deprotection of the t-Boc group under

various conditions and formation of complex mixtures, presumably due to free

NH present in the molecule. It was therefore decided to circumvent the use of a

protecting group and shorten the synthetic sequence by performing an Ullmann

coupling on the carbazole 2.13 prior to double Barton-Kellogg coupling.

Initially, the Ullmann coupling was planned to be carried out with 1-bromo-4-

iodobenzene to avoid di-substitution on the benzene ring. Various conditions

and catalysts such as Cu43 or CuI44–46 with L-proline47–49, 1,10-phenanthroline50 as

ligands in both toluene and DMF were screened, however, none of the described

methods displayed appreciable selectivity towards the iodine substituent and

either no conversion or a mixture of products (1:2 to 1:4, bromo:iodo-substituted


| 51

product) was always observed. We have therefore opted for the same approach

as in the case of carbazole 2.8 and used a large excess (6 equivalents) of 1,4-

idodobenzene (Scheme X). Conveniently, the unreacted 1,4-iodobenzene can be

recycled after the reaction by flash column chromatography due to its low

polarity. Finally, this procedure gave the N-substituted carbazole 2.14 in an

excellent yield of 91%.

Scheme 4. Double Barton-Kellogg coupling used to install the two molecular motor units.

At this point, the two motor units needed to be introduced in the molecule via

double Barton-Kellogg coupling (Scheme 5). The sequence started with a

thionation of the ketone 2.14 using Lawesson’s reagent in toluene at 95 °C. The

temperature had to be closely monitored as increase above 100 °C led to a quick

decomposition of the formed thioketone 2.15 presumably due to enolization,

followed by dimerization, trimerization and oligomerization of the thioenol.51,52

This side process could be distinguished by a formation of a yellow spot situated

at the start of the TLC plate. Isolation of the dithioketone by a short column,

followed by a reaction with 9-diazofluorenone 2.16a or 2.16b at 80 °C in toluene

and subsequent desulphurization of the resulting episulfides 2.17a-b with

HMPT afforded the building block 2.18a-b in 49% and 44% yield, respectively,

over three steps.


52 |

Scheme 5. Connection of the two halves 2.11 and 2.18a-b via Sonogashira coupling

Finally, the unpropelled part 2.11 and the motorized part 2.18a-b were

connected in a classical Sonogashira coupling, using a slight excess of the

alkyne. The final compounds 2.5a-b were isolated as a mixture of two

diastereomers since they were found to be inseparable by flash column

chromatography in all steps of the synthesis. It should be realized that only the

meso diastereomer can be effective for directional movement on a surface. In

case of the (R,R)- and (S,S)-isomers, the motor units rotate in a disrotatory

fashion with respect to each other, thus preventing the molecule from moving in

a linear manner. For this purpose, the diastereomers can be separated using

preparative HPLC or supercritical fluid chromatography (SFC) when required.

Photochemical and thermal isomerization studies in a solution

The photochemical and thermal isomerization behavior of 2.5a-b was examined

in solution using both low temperature UV-vis absorption and 1H NMR

spectroscopy to demonstrate that the rotary function of the two appending

motor units remained uncompromised.

The UV-vis absorption spectra of the dragsters 2.5a and 2.5b in heptane at 293 K

show absorption bands centered at 392 and 434 nm, respectively (Figure 8, black

solid).


| 53

Figure 8. UV-vis absorption spectra (heptane, 293 K) of stable 2.5a (a) and stable 2.5b (b)

(black solid); irradiation to PSS (365 nm) at 273 K (blue solid); and after heating the samples to 333 K (dashed red).

Irradiation of the sample with UV light (365 nm) at 273 K led to a red-shift of the

absorption bands to 401 and 436 nm, respectively, consistent with a formation of

a higher energy isomer, and hence species containing a more strained central

double bond.53 Throughout the irradiation, a single isosbestic point was

observed in each case, indicating that only a single motor unit undergoes

photochemical EZ isomerization at a time and that the irradiation does not

produce a double unstable form of 2.5a or 2.5b (based on 1H NMR spectroscopy

and presence of a single isosbestic point in UV-vis experiments). Samples were

irradiated until no further changes were observed and the photostationary state

(PSS) was reached (Figure 8, blue solid).

After heating the samples to 333 K, a complete recovery of the original UV-vis

absorption spectra were observed, consistent with the unstable form of 2.5a-b

undergoing thermal helix inversion back to the stable isomers (Figure 8, red

dashed).

The rate constants for the thermal helix inversion were measured at five

different temperatures (heptane) by following the UV-vis absorption spectra

over time. Multivariate analysis was performed on the array of the spectra,

providing the rate constant for each temperature. The Eyring plot was then

constructed and the activation parameters for the thermal process were derived

from the linear fit (Figure 9 and 10).


54 |

∆‡G°THI 88.4 ± 0.0

kJ.mol-1

∆‡H°THI 65.4 ± 0.2

kJ.mol-1

∆‡S°THI -79.5 ± 0.5

J.K-1.mol-1

k (293 K) (1.10 ± 0.05) × 10-3

s-1

t1/2 (293 K) 10.7 ± 0.0 min

Figure 9. (left) Thermodynamic data for the thermal helix inversion of the unstable 2.5a

to the stable 2.5a (heptane). (right) Eyring plot for the thermal process.

The Gibbs free energy of activation ∆‡G°THI for isomerization of the unstable 2.5a

was determined to be 88.4±0.0 kJ.mol-1 (∆‡H°THI 65.4±0.2 kJ.mol−1, ∆‡S°THI -

79.5±0.5 J.K−1.mol−1), corresponding to a half-life of 10.7±0.0 min at room

temperature (Figure 9, left). These values compare well to those reported for the

nanocar 2.4 which were found to be 88.0 kJ.mol-1 and a half-life of 9.1 min.37

∆‡G°THI 92.6 ± 0.1

kJ.mol-1

∆‡H°THI 67.2 ± 2.3

kJ.mol-1

∆‡S°THI -86.4 ± 7.5

J.K-1.mol-1

k (293 K) (1.95 ± 0.08) × 10-3

s-1

t1/2 (293 K) 59.2 ± 2.5 min

Figure 10. (left) Thermodynamic data for the thermal helix inversion of the unstable 2.5b

to the stable 2.5b (heptane). (right) Eyring plot for the thermal process.

Using the same procedure, the activation Gibbs energy ∆‡G°THI for the thermal

isomerization of the unstable 2.5b to the stable 2.5b was found to be 92.6±0.1

kJ.mol-1 (∆‡H°THI 67.2±2.3 kJ.mol−1, ∆‡S°THI -86.4±7.5 J.K−1.mol−1), corresponding

to a half-life 59.2±2.5 min at room temperature (Figure 10a). The increase of

∆‡G°THI is in accordance with introduction of phenyl substituents in the 2,7-

position of the fluorenyl rotors, resulting in increased steric hindrance in the

fjord region during the thermal helix inversion. One should realize that these

∆‡G°THI values are only relevant for measurements on surfaces at ambient

conditions, as in other instances, such as ultra-high vacuum STM at 7 K, the

barriers are thermally insurmountable and electron tunneling excitation by STM

tip must be used for induction of the thermal step regardless of the activation

barrier.


| 55

The switching behavior was further probed using 1H NMR spectroscopy. A

sample of 2.5a-b (2 mg) in chloroform-d3 was prepared. 1H NMR spectra were

recorded at 243 K before and after irradiation (at 233 K) with a hand-held UV-

lamp or LED using optical fiber inside the NMR spectrometer (both 365 nm) (3-

16 h). Unfortunately, in neither case a formation of a new set of NMR

absorptions was observed as a consequence of the irradiation, unlike in the case

of nanocar 2.4.37 Lowering the temperature further (223 K) did not improve the

situation. It remains unclear why no change was observed using 1H NMR

spectroscopy. Possible a much higher concentration than in the UV-vis

spectroscopy experiments, low quantum yield or a combination of thereof is

responsible for this.

Examining the photochemical and thermal behavior of 2.5a-b in solution using

UV-vis absorption, it can be concluded that the motor function of the

overcrowded alkenes is preserved in both molecules. The dragsters described

herein are therefore suitable candidate for investigation of a directional

movement on surfaces.

Single molecule STM experiments at ambient conditions

With the knowledge that the molecules 2.5a-b retained their molecular motor

function, we opted to perform preliminary scanning tunneling miscroscopy

(STM) experiments and study their behavior on surfaces under ambient

conditions. For this purpose, HOPG and gold were chosen as the surfaces for

modification with n-pentacontane. N-pentacontane is known to self-assemble on

surfaces and serve as a “ruler” and may exhibit attractive interactions with the

hexyl chains of the dragsters 2.5a-b, facilitating their absorption on the surface.

Upon preparation of the n-pentacontane modified HOPG, the sample was

examined by STM at the liquid-solid interface to ensure that the n-pentacontane

domains are large enough. Subsequently, a drop of the ~7.9× 10-5 M solution of

the dragster 2.5a in n-tetradecane was added. The pentacontane adlayer could

still be resolved after the addition of the dragster, however no dragsters were

observed in these experiments (Figure 13). Measurements on bare HOPG did

not lead to adsorption of the dragsters either.

For the experiments were performed on gold on mica substrates, a 400 nm-thick

layer of gold was deposited (in a home-built thermal deposition system) on a

freshly cleaved mica substrate at a temperature of 375°C and a pressure of 1.8 ×


56 |

10-6M. After flame annealing the substrate, a ~9.6 × 10-4M solution of n-

pentacontane in n-tetradecane was drop-casted on the gold/mica substrate. One

hour later, a ~7.9× 10-5M solution of the dragster 2.5a in n-tetradecane was drop-

casted on top of the pentacontane solution. In this system, the STM

measurements did not reveal adsorped dragster molecules, neither the

pentacontane adlayer. However, it is necessary to carry out more experiments in

order to conclude whether the dragsters are suitable for use on surfaces under

ambient conditions.

Figure 13. STM images of the n-pentacontane adlayer after deposition of the

dragster 2.5a.

Conclusions

Two molecular dragsters with different wheel size have been synthesized.

As anticipated, the motors units in the dragsters have been proven to undergo

photochemically driven rotation in a solution using UV-vis spectroscopy.

Kinetic experiments were performed and thermodynamic data for the thermal

helix inversion step of the rotary cycle have been determined by Eyring analysis.

The barriers of THI were found to be 88.4±0.0 kJ.mol-1 and 92.6±0.1 kJ.mol-1 for

2.5a and 2.5b respectively, which corresponds to a half-life of 10.7±0.1 and

59.2±2.5 min, respectively, at room temperature.

No movement of the molecules on the pentacontane modified surface has been

observed under UV irradiation (365 nm) in the preliminary STM measurements

5.0nm 10nm


| 57

so far, presumably due to strong attractive forces between the dragsters and the

surface.

Acknowledgment

The single molecule STM experiments on the surfaces described herein have

been performed by G. H. Heideman, who is gratefully acknowledged for this

contribution.

Experimental section

General remarks

Reagents were purchased from Aldrich, Merck or Fluka and were used as

provided unless otherwise stated. The solvents were distilled and dried, if

necessary, by standard methods. Column chromatography was performed on

silica gel (Merck type 9385 230-400 mesh) unless stated otherwise using positive

pressure, TLC: silica gel 60, Merck, 0.25 mm. High Resolution Mass spectra

(HRMS) were recorded on an LTQ Orbitrap XL. NMR spectra were obtained

using a a Varian Mercury Plus (1H: 400 MHz, 13C: 100 MHz), a Varian Unity Plus

(1H: 500 MHz, 13C: 125 MHz) or a Varian Innova (1H: 600 MHz,) in CDCl3, d8-

toluene or CD2Cl2. Chemical shifts are reported in δ units (ppm) relative to the

residual deuterated solvent signal of CDCl3 (1H NMR, δ 7.26 ppm; 13C NMR, δ

77.23 ppm), d8-toluene (1H NMR, δ 2.09 ppm), or CD2Cl2 (1H NMR, δ 5.32 ppm; 13C NMR, δ 54.0 ppm). The splitting patterns are designated as follows: s

(singlet), d (doublet), t (triplet), q (quartet), dd (doublet of doublets), td (triplet

of doublets), qt (quartet of triplets), m (multiplet) and br (broad). SFC was

performed on a Thar SFC system consisting of a fluid delivery module (FDM10-

1), an autosampler (a modified Alias 840), a semi-prep column oven, PDA

detector, a back-pressure regulator (ABPR20), heat-exchanger, and a fraction

collector (modified Thar SFC-FC). UV-vis absorption spectra were measured on

a Jasco V-630 or a Hewlett-Packard 8453 spectrometer. CD spectra were

measured on a Jasco J-815 CD spectrometer. Solvents used for spectroscopic

studies was of spectroscopic grade (UVASOL Merck). Irradiations were

performed using a spectroline ENB-280C/FE lamp (λmax = 365 nm), or an LED

(5 W, 365 nm, 10 nm width at half-height), mounted in a modified Nalorac Z-

Spec probe in the Varian Innova-600 NMR. Samples irradiated for 1H NMR

spectroscopy were placed 3-5 cm from the lamp. Irradiations at low


58 |

temperatures were performed in standard EtOH/N2 bath. Photostationary states

were determined by monitoring changes in UV-vis spectra or 1H NMR spectra

until no further changes were observed. Kinetic analysis of the thermal

isomerization steps was performed by UV-vis spectroscopy. Changes in UV-vis

absorptions were monitored at different temperatures. The array of the UV-vis

spectra was processed using multivariate analysis (from 200 to 800 nm) to obtain

the corresponding rate constants from which an Eyring plot was constructed.

∆‡G°, ∆‡H°, ∆‡S° and t1/2 (20 °C) were extracted from this plot.

STM visualization of 2.5a on HOPG

Prior to imaging, the n-pentacontane (TCI Europe) molecules were dissolved in

n-tetradecane (Sigma-Aldrich) by heating (40°C) and sonication for at least 2

hours. The non-volatile solvent n-tetradecane allows us to perform STM

measurements at the solid-liquid interface. A ~9.6 × 10-4 M solution of n-

pentacontane in n-tetradecane was drop-casted on a freshly cleaved highly

oriented pyrolytic graphite (HOPG) crystal (SPI supplies, SPI-3 grade). The STM

tips were prepared by mechanical cutting from Pt/Ir wire (90:10, diameter 0.25

mm, Goodfellow). All experiments were performed at room temperature using a

PicoSPM instrument (Molecular Imaging, Scientec) and PicoScan imaging

software.

Synthesis of the dragsters and intermediates

4,4'-Dibromo-2-nitro-1,1'-biphenyl (2.7).

Fuming nitric acid (92.5 %, 120 mL, 2.5 mol) was added into a

solution of 4,4'-dibromo-1,1'-biphenyl (29.0 g, 93 mmol) in

acetic acid (300 mL) over 10 min. The resulting suspension

was heated to 100 °C for 30 min. The solution was cooled down to 0 °C, and the

pale yellow solid was filtered through a glass filter. The solid was dried on air

and then triturated with ethanol (350 mL) to give the pure product 2.7. Yield:

27.53 g (83%). Pale yellow solid. Mp 124.3127.5 °C. 1H NMR (400 MHz, CDCl3):

δ (ppm) 8.03 (dd, 1H, J1 = 1.7 Hz, J2 = 1.7 Hz), 7.76 (ddd, 1H, J1 = 8.2 Hz, J2 = 1.8

Hz, J3 = 1.8 Hz), 7.57 (dd, 2H, J1 = 8.5 Hz, J2 = 1.6 Hz), 7.29 (dd, 1H, J1 = 8.2 Hz, J2

= 1.5 Hz), 7.16 (dd, 2H, J1 = 8.5 Hz, J2 = 1.6 Hz). 13C NMR (100 MHz, CDCl3): δ

(ppm) 136.8, 135.8, 135.5, 134.3, 133.2, 132.2, 129.6, 127.5, 123.3, 122.0.


| 59

2,7-Dibromo-9H-carbazole (2.8).

A mixture of the biphenyl 2.7 (28.5 g, 80 mmol) and

triphenylphosphine (52.3 g, 200 mmol) in 1,2-dichlorobenzene

(160 mL) was heated at 190 °C for 6 h. The solvent was then

distilled out at reduced pressure and the residue was purified by column

chromatography on silica gel (pentane : dichloromethane – 5 : 1 to 3 : 1) give the

pure carbazole 2.8. Yield: 20.3 g (78%). Tan solid. Mp 230.1231.8 °C. 1H NMR

(400 MHz, CDCl3): δ (ppm) 8.07 (s, 1H), 7.88 (d, 2H, J = 8.5 Hz), 7.58 (d, 2H, J =

1.6 Hz), 7.36 (dd, 2H, J1 = 8.5 Hz, J2 = 1.6 Hz). 13C NMR (100 MHz, CDCl3): δ

(ppm) 138.5, 129.4, 124.2, 123.3, 112.7, 112.2.

2,7-Dibromo-9-(4-iodophenyl)-9H-carbazole (2.9).

A mixture of the carbazole 2.8 (1.95 g, 6.0 mmol),

1,4-diiodobenzene (7.92 g, 24.0 mmol), 1,10-phenanthroline

(216 mg, 1.2 mmol), Cs2CO3 (3.91 g, 12.0 mmol) and CuI

(229 mg, 1.2 mmol) in toluene (30 mL) was heated at 110 °C.

When the starting material was completely consumed

(67 h, TLC), the solvents were evaporated at reduced pressure and the residue

was purified by column chromatography on silica gel (pentane to pentane :

dichloromethane – 5 : 1) to give the pure product 2.9. Yield: 2.43 g (77%). White

solid. Mp 188.1189.3 °C. 1H NMR (400 MHz, CDCl3): δ (ppm) 7.97 (d, 2H, J = 8.1

Hz), 7.93 (d, 2H, J = 8.3 Hz), 7.47 (s, 2H), 7.41 (d, 2H, J = 8.3 Hz), 7.25 (d, 2H, J =

8.1 Hz). 13C NMR (100 MHz, CDCl3): δ (ppm) 141.6, 139.7, 136.3, 129.0, 124.1,

121.9, 121.7, 120.3, 113.0, 93.5.

2,7-Dibromo-9-(4-iodophenyl)-9H-carbazole (2.10).

A mixture of the carbazole 2.9 (2.30 g, 4.36 mmol),

ethynyltrimethylsilane (620 l, 4.36 mmol), Pd(PPh3)2Cl2

(153 mg, 0.22 mmol) and CuI (42 mg, 0.22 mmol) in dry THF

(50 mL) and Et3N (25 mL) was degassed by four freeze-

pump-thaw cycles. The resulting solution was stirred at

room temperature under N2 atmosphere overnight. The volatiles were

evaporated at reduced pressure and the residue was purified by column

chromatography on silica gel (pentane to pentane : dichloromethane – 5 : 1) to

give the pure product 2.10. Yield: 1.78 g (82%). White solid. Mp 239.1240.3 °C. 1H NMR (400 MHz, CDCl3): δ (ppm) 7.93 (d, 2H, J = 8.3 Hz), 7.74 (d, 2H, J = 8.5

Hz), 7.49 (d, 2H, J = 1.2 Hz), 7.46 (d, 2H, J = 8.5 Hz), 7.41 (dd, 2H, J1 = 8.3 Hz, J2 =


60 |

1.5 Hz), 0.32 (s, 9H). 13C NMR (100 MHz, CDCl3): δ (ppm) 141.7, 136.4, 134.0,

126.9, 124.0, 123.4, 122.0, 121.7, 120.2, 113.2, 103.9, 96.3, 0.1.

9-(4-Ethynylphenyl)-2,7-bis(trimethylsilyl)-9H-carbazole (2.11).

The solution of carbazole 2.10 (710 mg, 1.4 mmol) in dry

THF (30 mL) was cooled down to -78 °C under nitrogen

atmosphere. Solution of n-BuLi (3.1 mL, 5.0 mmol) was

added dropwise over 10 minutes. After stirring for 30 min,

TMSCl (730 l, 5.7 mmol) was added at once and the

reaction was left to warm to room temperature. Aq. KOH (3 ml, 2 M) was added

and the mixture was stirred for 6 h. The reaction mixture was partitioned

between water (60 mL) and ethyl acetate (50 mL). The water layer was washed

with ethyl acetate (2 × 50 mL) and the combined organic extracts were dried

with MgSO4. The volatiles were evaporated at reduced pressure and the residue

was purified by column chromatography on silica gel (pentane : ethyl acetate –

50 : 1) to give the pure product 2.11. Yield: 505 mg (86%). White solid. Mp 221.6-

222.3 °C. 1H NMR (400 MHz, CDCl3): δ (ppm) 8.17 (d, 2H, J = 7.7 Hz), 7.81 (d,

2H, J = 8.3 Hz), 7.617.63 (m, 4H), 7.49 (d, 2H, J = 7.7 Hz), 3.24 (s, 1H), 0.36 (s,

18H). 13C NMR (100 MHz, CDCl3): δ (ppm) 140.4, 138.7, 138.4, 133.9, 127.1, 125.1,

124.2, 121.1, 120.0, 114.4, 83.2, 78.3, -0.5. HRMS (ESI+): calcd for C26H30NSi2+ (M +

H+) 412.1911 found 412.1909.

2,7-Dihexyl-9H-carbazole (2.12).

A solution of hexylmagnesium bromide (38.5 mL, 2.0 M in

Et2O) was added slowly to a degassed solution of 2.8 (5.0 g,

15.4 mmol) and Pd(dppf)Cl2 (450 mg, 0.62 mmol) in dry

THF (100 mL) at room temperature under N2 atmosphere. The resulting mixture

was then heated at reflux for 4 h. After no more starting material could be

observed by TLC, the reaction mixture was cooled down and the reaction was

quenched by slow addition of methanol (5 mL). The solvents were evaporated at

reduced pressure and the residue purified by column chromatography on silica

gel (pentane : dichloromethane – 5 : 1) to give the pure product 2.12. Yield: 4.21

g (81%). White flaky solid. 1H NMR (400 MHz, CDCl3): δ (ppm) 7.93 (d, 2H, J =

7.9 Hz), 7.76 (brs, 1H), 7.17 (s, 2H), 7.07 (dd, 2H, J1 = 8.0 Hz, J2 = 1.2 Hz), 2.78 (t,

4H, J = 7.7 Hz), 1.72 (m, 4H), 1.331.39 (m, 12H), 0.92 (t, 6H, J = 7.0 Hz). 13C NMR

(100 MHz, CDCl3): δ (ppm) 140.8, 140.1, 121.5, 120.4, 119.8, 110.2, 36.7, 32.1, 32.0,

29.3, 22.8, 14.3.


| 61

4,8-Dihexyl-2,10-dimethyl-10,11-dihydro-1H-dicyclopenta[c,g]carbazole-

3,9(2H,6H)-dione (2.13).

Methacrylic acid (10.4 mL, 122 mmol) was added to a

mechanically stirred mixture of the carbazole 2.12 (4.10 g,

12.2 mmoL) and in PPA (115 %, 100 mL) and heated at

100 °C overnight. The reaction was quenched by addition

of ice (300 mL) and the resulting mixture was extracted

with dichloromethane (3 x 100 mL). The combined organic extracts were washed

with sat. aq. K2CO3 (100 mL) and dried with MgSO4. The solvents were

evaporated at reduced pressure and the residue purified by column

chromatography on silica gel (dichloromethane) to give the pure product 2.13.

Yield: 1.94 g (34%). Pale yellow solid. Mp 197.5198.3 °C. 1H NMR (400 MHz,

CDCl3): δ (ppm) 8.91 (brs, 1H), 7.22 (s, 2H), 4.06 (dd, 2H, J1 = 17.0 Hz, J2 = 7.9

Hz), 3.143.36 (m, 6H), 2.802.91 (m, 2H), 1.641.72 (m, 4H), 1.401.46 (m, 10H),

1.281.38 (m, 8H) 0.88 (t, 6H, J = 7.0 Hz). 13C NMR (100 MHz, CDCl3): δ (ppm)

209.0, 208.9, 150.07, 150.04, 143.8, 143.0, 127.58, 127.55, 118.65, 118.63, 111.5, 42.3,

42.2, 36.9, 36.8, 32.5, 32.0, 31.2, 29.6, 22.9, 17.2, 17.0, 14.3.

4,8-Dihexyl-6-(4-iodophenyl)-2,10-dimethyl-10,11-dihydro-1H-

dicyclopenta[c,g]carbazole-3,9(2H,6H)-dione (2.14).

A mixture of the carbazole 2.13 (250 mg, 0.53 mmol),

1,4-diiodobenzene (1.05 g, 3.2 mmol), 1,10-phenanthroline

(38.2 mg, 0.21 mmol), Cs2CO3 (345 mg, 1.1 mmol) and CuI

(40.4 mg, 0.21 mmol) in toluene (2 mL) was heated to

110 °C. When the starting material was completely

consumed (67 h, TLC), the solvents were evaporated at

reduced pressure and the residue purified by column chromatography on silica

gel (dichloromethane to dichloromethane : ethyl acetate – 40 : 1) to give the pure

product 2.13. Yield: 321 mg (90 %). Pale yellow solid. Mp 79.781.6 °C. 1H NMR

(400 MHz, CDCl3): δ (ppm) 8.02 (d, 2H, J = 8.5 Hz), 7.23 (d, 2H, J = 8.4 Hz), 6.96

(s, 2H), 4.09 (dd, 2H, J1 = 16.8 Hz, J2 = 7.9 Hz), 3.303.37 (m, 2H), 3.043.23 (m,

4H), 2.792.89 (m, 2H), 1.58 (m, 4H), 1.261.44 (m, 18H), 0.87 (t, 6H, J = 7.0 Hz). 13C NMR (100 MHz, CDCl3): δ (ppm) 208.7, 208.6, 149.89, 149.85, 145.2, 143.3,

139.8, 136.3, 130.0, 128.1, 128.0, 118.69, 118.67, 110.6, 94.6, 42.33, 42.30, 37.1, 37.0,

32.7, 31.9, 31.5, 29.6, 22.9, 17.2, 17.0, 14.3. HRMS (ESI+): calcd for C38H45INO2+ (M

+ H+) 674.2489 found 674.2484.


62 |

General procedure for Barton-Kellogg coupling (2.18a-b).

A mixture of the diketone 2.14 (200 mg, 0.30 mmol)

and Lawesson’s reagent (480 mg, 1.2 mmol) in dry

toluene (20 mL) was heated at 90 °C for 3 h. The

mixture was left to cool down to room temperature

and passed through a short column of silica gel. The

dithioketone was eluted (pentane : ethyl acetate –

10 : 1) as the first red band. The solvents were

evaporated at reduced pressure and the residue was

redissolved in dry toluene (20 mL). The solution was heated to 80 °C and

diazofluorenone54 or 2,7-biphenyldiazofluorenone (1.05 mmol) was added at

once. The resulting solution was heated at 80°C overnight. HMPT (160 l, 0.89

mmol) was added and the mixture was heated for additional 3 h. The solvents

were evaporated at reduced pressure and the residue was purified by column

chromatography.

3,9-Di(9H-fluoren-9-ylidene)-4,8-dihexyl-6-(4-iodophenyl)-2,10-dimethyl-

2,3,6,9,10,11-hexahydro-1H-dicyclopenta[c,g]carbazole (2.18a).

Prepared according to the general procedure from the ketone 2.14 (200 mg, 0.30

mmol) and diazafluorenone (228 mg, 1.2 mmol). The product was purified by

column chromatography on silica gel (pentane : dichloromethane - 7:1 to 5:1) to

give 2.18a as a mixture of diastereomers (~ 1:1). Yield: 132 mg (46 %). Orange

solid. Mp >250 °C (decomp.). 1H NMR (400 MHz, CDCl3): δ (ppm) 8.04 (dd, 2H,

J1 = 8.3 Hz, J2 = 2.4 Hz), 7.93 (dd, 2H, J1 = 7.2 Hz, J2 = 7.2 Hz), 7.81 (dd, 2H, J1 =

7.6 Hz, J2 = 7.6 Hz), 7.75 (d, 1H, J = 7.6 Hz), 7.71 (d, 1H, J = 7.5 Hz), 7.61 (d, 1H, J

= 7.9 Hz), 7.49 (dd, 2H, J1 = 8.2 Hz, J2 = 8.2 Hz), 7.45 (d, 1H, J = 8.3 Hz), 7.307.40

(m, 4H), 7.26 (dd, 2H, J1 = 7.7 Hz, J2 = 7.4 Hz), 7.20 (d, 1H, J = 7.9 Hz), 7.14 (s,

1H), 7.12 (s, 1H), 7.08 (dd, 1H, J1 = 7.5 Hz, J2 = 7.5 Hz), 7.02 (dd, 1H, J1 = 7.6 Hz, J2

= 7.6 Hz), 4.30 (m, 2H), 3.87 (dd, 1H, J1 = 14.9 Hz, J2 = 5.6 Hz), 3.75 (dd, 1H, J1 =

15.2 Hz, J2 = 5.6 Hz), 3.41 (d, 1H, J = 15.0 Hz), 3.20 (d, 1H, J = 15.0 Hz), 3.07 (m,

2H), 2.64 (m, 2H), 1.50 (d, 3H, J = 6.5 Hz), 1.331.43 (m, 7H), 0.881.11 (m, 12H),

0.68 (t, 3H, J = 7.4 Hz), 0.64 (t, 3H, J = 7.4 Hz). 13C NMR (100 MHz, CDCl3): δ

(ppm) 153.0, 152.9, 143.4, 143.2, 141.5, 141.4, 140.5, 140.2, 139.99, 139.95, 139.8,

139.6, 139.5, 139.15, 139.11, 138.3, 138.1, 137.5, 137.4, 133.6, 133.5, 130.0, 129.7,

128.6, 128.5, 127.05, 127.01, 126.99, 126.95, 126.6, 126.59, 126.54, 123.8, 122.8,

119.82, 119.80, 119.4, 119.33, 119.30, 119.2, 108.9, 108.8, 93.4, 93.1, 44.9, 44.3, 43.3,

43.1, 35.1, 35.0, 32.8, 32.5, 31.8, 31.7, 28.76, 28.75, 22.66, 22.61, 20.0, 19.6, 14.19,

14.15. HRMS (ESI+): calcd for C64H61IN+ (M + H+) 970.3843 found 970.3823.


| 63

3,9-Bis(2,7-diphenyl-9H-fluoren-9-ylidene)-4,8-dihexyl-6-(4-iodophenyl)-2,10-

dimethyl-2,3,6,9,10,11-hexahydro-1H-dicyclopenta[c,g]carbazole (2.18b).

Prepared according to the general procedure from the ketone 2.14 (200 mg, 0.30

mmol) and 2,7-diphenyldiazafluorenone (360 mg, 1.08 mmol). The product was

purified by column chromatography on silica gel (pentane : dichloromethane -

5:1 to 3:1) to give 2.18b a mixture of diastereomers (~1:1). Yield: 195 mg (52 %).

Orange solid. Mp >250 °C (decomp.). 1H NMR (400 MHz, CDCl3): δ (ppm) 8.19

(d, 2H, J = 8.4 Hz), 8.10 (d, 2H, J = 8.2 Hz), 7.96 (s, 1H), 7.88 (dd, 2H, J1 = 7.2 Hz,

J2 = 7.2 Hz), 7.82 (m, 3H), 7.73 (dd, 4H, J1 = 7.8 Hz, J2 = 7.8 Hz ), 7.607.64 (m, 4

H), 7.287.52 (m, 18H), 7.22 (s, 1H), 7.17 (s, 1H), 4.40 (m, 2H), 3.89 (dd, 1H, J1 =

15.0 Hz, J2 = 5.7 Hz), 3.80 (dd, 1H, J1 = 15.1 Hz, J2 = 5.7 Hz), 3.45 (d, 1H, J = 15.2

Hz), 3.22 (m, 3H), 2.712.76 (m, 2H), ), 1.59 (d, 3H, J = 6.5 Hz), 1.381.45 (m, 7H),

0.891.12 (m, 12H), 0.69 (t, 3H, J = 6.9 Hz), 0.63 (t, 3H, J = 6.8 Hz). 13C NMR (100

MHz, CDCl3): δ (ppm) 153.56, 153.42, 143.66, 143.37, 142.37, 142.23, 141.87,

141.76, 141.74, 141.68, 140.92, 140.87, 140.53, 140.42, 140.11, 140.06, 139.69, 139.62,

139.36, 139.31, 139.24, 139.09, 138.71, 138.00, 137.95, 137.62, 133.65, 133.50, 129.89,

129.48, 129.10, 128.75, 128.71, 128.52, 128.46, 127.42, 127.36, 127.29, 127.27, 127.12,

127.02, 126.97, 126.1, 125.95, 125.92, 122.82, 122.78, 121.50, 121.47, 120.3, 120.2,

119.86, 119.76, 119.52, 119.3, 108.94, 108.89, 93.6, 93.1, 44.7, 44.3, 43.3, 43.2, 35.4,

35.3, 33.0, 32.8, 31.84, 31.77, 28.82, 28.81, 22.67, 22.60, 20.12, 19.7, 14.19, 14.14.

HRMS (APCI+): calcd for C88H76IN+ (M+) 1273.5011 found 1273.5017.


64 |

General procedure for Sonogashira coupling of 2.18a-b and 2.11.

A mixture of aryl iodide 2.18a-b (1 eq.), ethyne 2.11 (1.6-1.8 eq), Pd(PPh3)2Cl2 (5

% mmol) and CuI (5 % mmol) in dry THF (5 mL) and Et3N (5 mL) was degassed

by four freeze-pump-thaw cycles. The resulting solution was stirred at room

temperature under N2 atmosphere overnight. The volatiles were evaporated at

reduced pressure and the residue was purified by column chromatography.

6-(4-((4-(2,7-Bis(trimethylsilyl)-9H-carbazol-9-yl)phenyl)ethynyl)phenyl)-3,9-

di(9H-fluoren-9-ylidene)-4,8-dihexyl-2,10-dimethyl-2,3,6,9,10,11-hexahydro-

1H-dicyclopenta[c,g]carbazole (2.5a).

Prepared according to the general procedure from 2.18a (194 mg, 0.20 mmol)

and 2.11 (154 mg, 0.37 mmol). The product was purified by column

chromatography on silica gel (pentane : dichloromethane - 7:1 to 5:1) to give

2.18a as a mixture of diastereomers (~ 1:1). Yield: 236 mg (94 %). Orange wax. 1H

NMR (400 MHz, CDCl3): δ (ppm) 8.11 (d, 2H , J = 7.6 Hz), 7.687.95 (m, 12H),

7.597.65 (m, 3H), 7.407.51 (m, 3H), 7.167.39 (m,10H), 7.08 (dd, 1H, J1 = 7.6 Hz,

J2 = 7.6 Hz), 7.02 (dd, 1H, J1 = 7.7 Hz, J2 = 7.7 Hz), 4.30 (m, 2H), 3.87 (dd, 1H, J1 =

15.3 Hz, J2 = 5.5 Hz), 3.77 (dd, 1H, J1 = 15.1 Hz, J2 = 5.6 Hz), 3.42 (d, 1H, J = 14.9

Hz), 3.20 (d, 1H, J = 15.0 Hz), 3.06 (m, 2H), 2.63 (m, 2H), 1.50 (d, 3H, J = 6.5 Hz),

1.331.43 (m, 8H), 0.881.11 (m, 12H), 0.67 (t, 3H, J = 7.4 Hz), 0.63 (t, 3H, J = 7.4

Hz), 0.30 (s, 18H). 13C NMR (100 MHz, CDCl3): δ (ppm) 153.12, 152.97, 143.50,

143.31, 141.52, 141.51, 140.61, 140.50, 140.29, 140.02, 139.98, 139.85, 139.17, 139.12,

138.79, 138.35, 138.29, 138.27, 138.20, 137.80, 137.74, 134.89, 133.73, 133.66, 133.61,


| 65

133.53, 129.29, 128.62, 128.56, 128.15, 127.84, 127.24, 127.06, 127.01, 126.96, 126.68,

126.61, 126.55, 125.19, 124.54, 124.31, 123.90, 123.21, 122.92, 122.87, 121.96, 121.94,

120.51, 120.10, 119.83, 119.56, 119.40, 119.37, 119.33, 114.48, 109.11, 109.06, 90.36,

90.27, 89.76, 89.70, 44.97, 44.37, 43.38, 43.22, 35.13, 35.04, 32.82, 32.56, 31.83, 31.75,

29.92, 28.79, 28.77, 27.14, 22.67, 22.62, 20.08, 19.64, 14.20, 14.15, -0.57. HRMS

(ESI+): calcd for C90H88N2Si2+ (M+) 1253.6481 found 1252.6472.

6-(4-((4-(2,7-Bis(trimethylsilyl)-9H-carbazol-9-yl)phenyl)ethynyl)phenyl)-3,9-

bis(2,7-diphenyl-9H-fluoren-9-ylidene)-4,8-dihexyl-2,10-dimethyl-2,3,6,9,10,11-

hexahydro-1H-dicyclopenta[c,g]carbazole (2.5b).

Prepared according to the general procedure from 2.18b (190 mg, 0.15 mmol)

and 2.11 (98 mg, 0.24 mmol). The product was purified by column

chromatography on silica gel (pentane : dichloromethane - 5:1 to 3:1) to give

2.18b as a mixture of diastereomers (~ 1:1). Yield: 195 mg (84 %). Orange wax. 1H NMR (400 MHz, CDCl3): δ (ppm) 8.19 (d, 2H, J = 9.9 Hz), 8.14 (d, 2H, J = 7.7

Hz), 7.978.01 (m, 3H), 7.777.93 (m, 6 H), 7.217.75 (m, 35H), 4.41 (m, 2H), 3.92

(dd, 1H, J1 = 15.0 Hz, J2 = 5.6 Hz), 3.83 (dd, 1H, J1 = 15.0 Hz, J2 = 5.5 Hz), 3.48 (d,

1H, J = 15.2 Hz), 3.22 (m, 3H), 2.74 (m, 2H), ), 1.59 (d, 3H, J = 6.6 Hz), 1.361.47

(m, 7H), 0.821.12 (m, 12H), 0.69 (t, 3H, J = 6.9 Hz), 0.63 (t, 3H, J = 6.8 Hz), 0.33

(s, 18H). 13C NMR (100 MHz, CDCl3): δ (ppm) 153.63, 153.49, 143.73, 143.43,

142.44, 142.39, 142.26, 141.89, 141.77, 141.73, 141.68, 140.94, 140.89, 140.53, 140.50,

140.42, 140.14, 140.08, 139.35, 139.30, 139.27, 139.11, 138.80, 138.72, 138.35, 138.32,

138.01, 137.95, 137.84, 137.80, 133.71, 133.68, 133.53, 129.16, 129.11, 128.95, 128.79,

128.74, 128.49, 128.45, 128.14, 128.03, 127.57, 127.44, 127.39, 127.31, 127.27, 127.16,

127.05, 126.99, 126.04, 125.95, 125.21, 124.32, 123.26, 122.98, 122.84, 122.80, 121.94,

121.52, 120.97, 120.25, 120.19, 120.11, 119.86, 119.76, 119.59, 119.38, 114.49, 109.15,

109.07, 90.54, 90.45, 89.70, 89.67, 44.63, 44.27, 43.37, 43.23, 35.39, 35.28, 33.02,

32.82, 31.87, 31.79, 29.92, 28.85, 27.14, 22.69, 22.61, 20.15, 19.73, 14.15, -0.56.

HRMS (ESI+): calcd for C114H105N2Si2+ (M + H+) 1557.7811 found 1557.7751.


66 |

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