Light-Driven Molecular MotorsSymposium ‘Transport on the Edge’

Friday, June 18, 2004

Eek Huisman

Supervisor: Dr. R. A. van Delden

?

What is a (molecular)

motor?

Oxford English Dictionary:‘A machine or mechanical agency which

imparts motion’

A molecular motor should1:• overcome Brownian motion• be unidirectional• perform the same cycle of movements a large number of times• convert energy into work

1 B. L. Feringa, N. Koumura, R. A. van Delden and M. K. J. ter Wiel, Appl. Phys. A. 75, 301 (2002)

Are there any fundamental differences between

macroscopic and molecular motors?

Thermal Motion

Thermal energy ~ Thermal energy at roomtemperature ~kbT = 4 . 10-21 J

M=4 . 10-25 kg

v=1 .102 m/s M=400 kg

v=3 .10-12 m/s

vsol=3 .102 m/s

Msol=4 . 10-26 kg

HOW TO CONTROL

MOLECULAR MOTION?

How to control molecular motion?

I) Energy input:• Light• Chemicals• Electro chemicals

II) Proper molecular geometry

III) Mechanism that ensures unidirectional motion

Energy input: light

Energy input: light

Charge transfer

+ +A B

hv

A*

B +A+

B-

hv

Cis-trans isomerization

Molecular Geometries

Rotaxanes

Catenanes

Others

3 EXAMPLES

Example 1: A linear motor 2

• [2]-rotaxane: thread and ring

• Two stations: change of affinity upon charge transfer (triplet excited state!)

• Hydrogen bonds

2 A. M. Brouwer, C. Frochot, F. G. Gatti, D. A. Leigh, L. Mottier, F. Paolucci, S. Roffia and G. W. H. Wurpel, Science 291, 2124 (2001)

Example 2: A rotary catenane motor 3

• [3]-catenane: 1 static ring, 2 gliding rings

• Static ring: 4 stations

– 2 stations susceptible to cis-trans isomerization: A and B (A’, B’)

– 2 other stations C and D

– affinity with the gliding rings: A>B>C>D>A’>B’

• Hydrogen bonds

3 D. A. Leigh, J. K. Y. Wong, F. Dehez and F. Zerdetto, Nature 424, 174 (2003)

affinity with the gliding

rings A>B>C>D>A

’>B’

Example 3: A rotary motor with a rigid axis4

• Sterically overcrowded alkene• Cis-trans isomerization causes rotation• Isomerization is followed by a an irreversible

thermal step• Steric hindrance of methyl group is crucial

4 N. Koumura, R. W. J. Zijlstra, R. A. van Delden, N. Harada and B. L. Feringa, nature 401, 152 (1999)

Studium Generale Lezing 30-10-2002

(P,P)-trans (M,M)-cis

MeeqMeeqMeax

Meax

Meax MeaxMeeq

Meeq

(P,P)-cis(M,M)-trans

> 280 nm

> 380 nm

> 280 nm

> 380 nm

20oC 60oC

1

2

3

4

1

2

3

4

Overview

Brouwer et al. Leigh et al. Feringa et al.

Kind of motion

linear rotary rotary

Molecular geometry

[2]-rotaxane [3]-catenane Overcrowded alkene

Mechanism Electron transfer (H-bonds)

Cis-trans

(H-bonds)

Cis-trans

Stimuli per cycle

1 6 4 (2)

Overall rate 104 Hz ~10-5 Hz ~10-4 Hz

WHAT CAN WE DO WITH

MOLECULAR MOTORS?

Applications

Molecular muscle

Modification of surfaces

Color change of LCD

Logic gates and switches

 

                  

                     

                  

                     

                  

                     

                            

2 meter

0.000000002 meter

‘I have no doubt that it is possible to give a new direction to technological development, a direction that shall

lead it back to the real needs of man, and that also means: to the actual size of man. Man is small, and, therefore,

small is beautiful.’

Ernst Friedrich Schumacher (1911–1977), economist