1. Light-Driven Molecular Motors Symposium ‘Transport on the Edge’ Friday, June 18, 2004 Eek Huisman Supervisor: Dr. R. A. van Delden

2. ?

3. What is a (molecular) motor?

4. Oxford English Dictionary: ‘A machine or mechanical agency which imparts motion’

5. A molecular motor should 1 : 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)

6. Are there any fundamental differences between macroscopic and molecular motors?

7. Thermal Motion Thermal energy ~ Thermal energy at roomtemperature ~k b T = 4. 10 -21 J M=4. 10 -25 kg v=1. 10 2 m/s M=400 kg v=3. 10 -12 m/s v sol =3. 10 2 m/s M sol =4. 10 -26 kg

9. HOW TO CONTROL MOLECULAR MOTION?

10. How to control molecular motion? I) Energy input: Light Chemicals Electro chemicals II) Proper molecular geometry III) Mechanism that ensures unidirectional motion

11. Energy input: light

12. Charge transfer + + AB hv A*A* B + A+A+ B-B- Cis-trans isomerization

13. Molecular Geometries Rotaxanes Catenanes Others

14. 3 EXAMPLES

15. 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)

17. 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)

18. affinity with the gliding rings A>B>C>D>A’>B’

19. Example 3: A rotary motor with a rigid axis 4 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)

20. Studium Generale Lezing 30-10-2002 1 2 3 4  1 2 3 4

22. Overview Brouwer et al.Leigh et al.Feringa et al. Kind of motion linearrotary Molecular geometry [2]-rotaxane[3]-catenaneOvercrowded alkene Mechanism Electron transfer (H-bonds) Cis-trans (H-bonds) Cis-trans Stimuli per cycle 164 (2) Overall rate 10 4 Hz~10 -5 Hz~10 -4 Hz

23. WHAT CAN WE DO WITH MOLECULAR MOTORS?

24. Applications Molecular muscle Modification of surfaces Color change of LCD Logic gates and switches

26. 2 meter 0.000000002 meter

27. ‘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