U NIVERSITA DEGLI S TUDI DI P ADOVA Corso CFMA. LS-SIMat1 Chimica Fisica dei Materiali Avanzati Part...

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



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



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



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



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



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



Mechanism: increase of the conjugationMechanism: increase of the conjugation

Open ring, parallel conformation

Open ring, antiparallel conformation

Closed ring



Other photochromic switchesOther photochromic switches

Cis-trans isomerization of azobenzenes

Switching of a spiropyran derivative

(c = closed, o = open)

Photochemical transformations of fulgides



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.


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


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


Photoinduced trans cis trans isomerization cyclesPhotoinduced trans cis trans isomerization cycles

N

N

N N

N

N

N

N

Ē

rotationaldiffusionh

h

STOPtrans cis


Reversible photoinduced Reversible photoinduced orientationorientation

of azobenzene groupsof azobenzene groups

C ircu la r P o l.

L in ear P o l.


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)


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


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



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



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



Towards molecular logic gatesTowards molecular logic gates



Electronic vs. ‘chemical’ computersElectronic vs. ‘chemical’ computers



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



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



Natural Molecular Machines and Motors - Natural Molecular Machines and Motors - 22

Rotary motor proteinsATP Synthase

Bacterial flagellar motor

Linear motor proteinsMyosin

Kinesin

Dynein



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



Photocontrolled Opening-Closing of Molecular Photocontrolled Opening-Closing of Molecular CavitiesCavities

Azobenzene containing macrotricyclic receptors

Azobenzene capped β-cyclodextrin



A Photochemically Driven Molecular Rotary A Photochemically Driven Molecular Rotary MotorMotor

B.L. Feringa et al., Nature, 1999, 401, 152



Photochemically Driven Threading-Photochemically Driven Threading-Dethreading Motions in PseudorotaxanesDethreading Motions in Pseudorotaxanes



Undirectional Circumrotation of Macrocycles in Undirectional Circumrotation of Macrocycles in CatenanesCatenanes

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