u niversita degli s tudi di p adova corso cfma. ls-simat1 chimica fisica dei materiali avanzati part...
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UUNIVERSITA’ DEGLI NIVERSITA’ DEGLI SSTUDI DI TUDI DI PPADOVAADOVAUUNIVERSITA’ DEGLI NIVERSITA’ DEGLI SSTUDI DI TUDI DI PPADOVAADOVA
Corso CFMA. LS-SIMat 1
Chimica Fisica dei Materiali AvanzatiChimica Fisica dei Materiali Avanzati
Part 8 – Molecular switches and molecular Part 8 – Molecular switches and molecular machinesmachines
Laurea specialistica in Scienza e Ingegneria dei MaterialiCurriculum Scienza dei Materiali
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Corso CFMA. LS-SIMat 2
Molecular-level devicesMolecular-level devicesMolecular-level electronic components Molecular-level systems that play the same functions played by
macroscopic components in electronic devices
Molecular-level mechanical machines Molecular-level systems that perform mechanical movements
analogous to those observed in macroscopic machines
Molecular-level electronic components
Molecular wires Molecular switches Molecular antennas Charge-separation devices Molecular memories Molecular sensors Molecular logic gates
Molecular-levelmechanical machines
Molecular tweezers, doors and boxes
Rotary motors Piston/cylinder systems Molecular shuttles and muscles Sliding molecular rings
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Corso CFMA. LS-SIMat 3
Switching of electron or energy transfer processesSwitching of electron or energy transfer processes
Switching requires an external stimulus which, at the molecular level, causes electronic and nuclear rearrangements. Usually one of the two types of rearrangements prevails or is more relevant to the performed function.
The three main types of stimuli that can be used to switch a chemical compound are:
Light energyLight energy (photons)Electrical energyElectrical energy (electrons or holes)Chemical energyChemical energy (in the form of reactants)
A C
A C
e- or E e- or E
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Corso CFMA. LS-SIMat 4
Molecular switchesMolecular switches
A molecular switch is a system on the molecular scale which can be reversibly brought from one state into another by means of an external stimulus.
Important properties for practical applications: thermal irreversibility quick response high efficiency fatigue resistance nondestructive readout
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Corso CFMA. LS-SIMat 5
Example: diarylethene switchesExample: diarylethene switches
First described by Irie in 1988. M. Irie, M. Mohri, J. Org. Chem. 53 (1988), 803-808
Reaction is thermally irreversible, response is quick, efficiency
and fatigue resistance are high.
Many studies have been performed on diarylethenes, with as main goals improving the switching properties and achieving non-destructive read-out. For an extensive review, see: M. Irie, Chem. Rev. 100 (2000),
1685-1716
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Corso CFMA. LS-SIMat 6
Photochromic response of diarylethenePhotochromic response of diarylethene
A very broad absorption extending over most of the visible range appears upon UV irradiation and ring closure
The process can be reversed by irradiation with > 500 nm
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Corso CFMA. LS-SIMat 7
Mechanism: increase of the conjugationMechanism: increase of the conjugation
Open ring, parallel conformation
Open ring, antiparallel conformation
Closed ring
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Corso CFMA. LS-SIMat 8
Other photochromic switchesOther photochromic switches
Cis-trans isomerization of azobenzenes
Switching of a spiropyran derivative
(c = closed, o = open)
Photochemical transformations of fulgides
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Corso CFMA. LS-SIMat 9
Optical memories by holographic Optical memories by holographic recordingrecording
Holographic optical storage is a unique method for achieving high-density data storage in three dimensions.
Photopolymer systems are quite attractive because of their high sensitivity, ease of preparation, and self-development capability.
Rewritable holographic recording materials based on photochromic conversion have attracted strong interest for three-dimensional optical recording
Photochromic cyclability
Holographic writing set-upA phase hologram with n = 1.15x10-3 and period dependent on the angle 2 is written.
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n
*N
N RN
O
CH3
CH2 C
CO
Methacrylic backbone
Optically active cyclic group
Conjugated trans-azoaromatic chromophore
R = CN, NO2
poly[(S)-MAP-C] R = CN Mn=43,900Mw /Mn=1.4 Tg=192°C Td= 311°C
poly[(S)-MAP-N] R = NO2 Mn=18,300Mw /Mn=1.4 Tg=208°C Td= 315°C
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200 300 400 500 600 7000.000
0.002
0.004
0.006
0.008
0.010
poly[(S)-MAP-C], film 120 nm poly[(S)-MAP-N], film 140 nm
632.8 nm488.0 nm
Abs
orpt
ion
coef
fici
ent/n
m-1
Wavelength/nm
Absorption in the visible:
azo-dyes n *, * and CT el. trans.
Pump @ 488 nmProbe @ 633 nm
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Photoinduced trans cis trans isomerization cyclesPhotoinduced trans cis trans isomerization cycles
N
N
N N
N
N
N
N
Ē
rotationaldiffusionh
h
STOPtrans cis
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Reversible photoinduced Reversible photoinduced orientationorientation
of azobenzene groupsof azobenzene groups
C ircu la r P o l.
L in ear P o l.
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30 60 90 120 150 180 210 240 2700.005
0.006
0.007
0.008
//K
K
Linear Dichroism
Irra
diat
ion
with
LP
light
Irra
diat
ion
with
CP
light
Abs
. coe
ff. K
(nm
-1)
Time (s)
30 60 90 120 150 180 210 240 270 300 3300.00
0.02
0.04
0.06
0.08
0.10
0.12
0.14
Birefringence
Irra
diat
ion
with
CP
light
Irra
diat
ion
with
LP
light
n2
n1
n
Time (s)
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250 300 350 400 450 500 550 600 650-0.25
-0.20
-0.15
-0.10
-0.05
0.00
0.05
0.10
0.15 Native irr. LP light irr. CP-L light irr. CP-R light
Elli
ptic
ity [
mde
g/nm
]
Wavelength [nm]
300 350 400 450 500 550 600 650-0.20
-0.15
-0.10
-0.05
0.00
0.05
0.10
0.15 Native Irr. CP-L light Irr. CP-R light
Elli
ptic
ity [
mde
g/nm
]
Wavelength [nm]
poly[(S)-MAP-N] Tg = 208 Cthin films 100 300 nmI 160 mW/cm2 x 60 s
Reversible inversionof the CD signal byirradiation with CP-L light
L. Angiolini et al., Chem. Eur. J., 8 (2002) 4241
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Photomodulation of linear
birefringence and dichroism
PHOTORESPONSIVE PROPERTIES
CONVENTIONAL MATERIALS
CHIROPTICAL SWITCHES
OPTICAL STORAGE
AND
CHIROPTICAL SWITCHES
CHIRALPHOTOCHROMIC
POLYMERS
Photomodulation of chiroptical properties
OPTICAL STORAGE
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Corso CFMA. LS-SIMat 17
Switching of electron transfer by a photon Switching of electron transfer by a photon inputinput
Light switching of electron transfer in multicomponent molecular systems based on the 1,2-bis-(3-thienyl)-ethene photochromic bridge
In the closed form energy is transferred to the conjugated diarylethene unit instead of electron transferred to the pyridinium ion
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Corso CFMA. LS-SIMat 18
Multistate-multifunctional supramolecular Multistate-multifunctional supramolecular systemssystems
Multistate systems : compounds that can be reversibly interconverted between more than two stable states
Multifunctional systems : compounds that can be reversibly interconverted between stable states by means of different stimuli Two photochromic units can be coupled in the same
supramolecular species, giving biphotochromic multistate systems The photochemical inputs used to stimulate photochromic
compounds can be couped with several other types of stimuli, leading to a variety of interesting multistate-multifunctional systems
On application of n independent stimuli, each related to 2 states, 2n different states of the system become available in principle
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Corso CFMA. LS-SIMat 19
Towards molecular logic gatesTowards molecular logic gates
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Corso CFMA. LS-SIMat 20
Electronic vs. ‘chemical’ computersElectronic vs. ‘chemical’ computers
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Corso CFMA. LS-SIMat 21
Molecular-level machinesMolecular-level machines
A molecular machine is a particular type of a molecular device whose outcome is a mechanical motion, i.e., in which the component parts can be set in motion as a result of some external stimulus
What are the possibilities of small but movable machines? [...]
Lubrication might not be necessary. Bearings could run dry; they wouldn’t run hot because heat escapes from such a small device very, very rapidly. [...]
An internal combustion engine of that size is impossible. Other chemical reactions, liberating energy when cold, can be used instead. [...]
What would be the utility of such machines? Who knows? [...]
I cannot see exactly what would happen, but I can hardly doubt that when we have some control of things on a molecular scale we will get an enormously greater range of possible properties that substances can have, and of the different things we can do.
R. P. Feynman, Address to the American Physical Society, December 1959
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Corso CFMA. LS-SIMat 22
Natural Molecular Machines and MotorsNatural Molecular Machines and Motors
Cells have hundreds of different types of molecular motors, each specialized for a particular function. Many biological motor-like proteins have been discovered and characterized in recent years.
(Natural) molecular motors come in a wide variety of designs. Some motors operate in a cyclic fashion, undergoing a number of steps that correspond to changes in conformation and/or in chemical state, and eventually resetting themselves to their initial configuration.
Copernicus, Springer - Verlag, New York, 1996
C. Bustamante, D. Keller, G. Oster, Acc. Chem. Res., 2001, 34, 412-420
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Corso CFMA. LS-SIMat 23
Natural Molecular Machines and Motors - Natural Molecular Machines and Motors - 22
Rotary motor proteinsATP Synthase
Bacterial flagellar motor
Linear motor proteinsMyosin
Kinesin
Dynein
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Corso CFMA. LS-SIMat 24
Artificial molecular machines: molecular Artificial molecular machines: molecular tweezerstweezers
Macroscopic tweezers
Molecular tweezers (photochemically controlled)
S. Shinkai et al., J. Am. Chem. Soc., 1981, 103, 111
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Corso CFMA. LS-SIMat 25
Photocontrolled Opening-Closing of Molecular Photocontrolled Opening-Closing of Molecular CavitiesCavities
Azobenzene containing macrotricyclic receptors
Azobenzene capped β-cyclodextrin
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Corso CFMA. LS-SIMat 26
A Photochemically Driven Molecular Rotary A Photochemically Driven Molecular Rotary MotorMotor
B.L. Feringa et al., Nature, 1999, 401, 152
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Corso CFMA. LS-SIMat 27
Photochemically Driven Threading-Photochemically Driven Threading-Dethreading Motions in PseudorotaxanesDethreading Motions in Pseudorotaxanes
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Corso CFMA. LS-SIMat 28
Undirectional Circumrotation of Macrocycles in Undirectional Circumrotation of Macrocycles in CatenanesCatenanes