1. Paper Introduction 5th Aug 2010
Rotary Molecular Motors: A Large Increase in Speed through a Small Change in Design
Tatiana Fernandez Landaluce1, Gabor London, Michael M. Pollard,2 Petra Rudolf,3 and Ben L. Feringa3
1. Centre for Systems Chemistry, Stratingh Institute for Chemistry, University of Groningen, Nijenborgh 4, 9747 AG . Groningen, The Netherlands.
2. Department of Chemistry, York University, Toronto, ON, Canada
3. Zernike Institute for Advanced Materials, University of Groningen, The Netherlands
The journal of organic chemistry
July 2, 2010

2. Asymmetric catalysis
Chirality
Biomimetic and catalytic oxidation
Organogels and smart materials
Molecular switches and motors

3. Switchable molecular motor

4. Unidirectional rotation of light driven molecular motor
Rotational cycle
UV irradiation
Thermal helix inversion (equatorial)
Repeat 1 & 2

5. Present work……….. Synthesis of 3
Effect of the steric interactions in the fjord region on the speed of the rotation at 25 oC.
Synthesis of 3

6. Unidirectional rotation of motor 3
Step-1, photochemical
Step-2, thermal
Unstable-3

7. Photochemical behavior
UV-vis spectrum of 3 in methylcyclo-hexane/ methylcylopentane at -153 oC (black) and after irradiation at 365 nm for 30 min (dotted).
Shifted band indicates formation of unstable-3
At room temperature identical spectra of stable-3 regenerated indicating thermal isomerization

8. Thermal behavior (1H NMR)
500 MHz 1H NMR spectra of stable-3 in THF at –98oC

9. After 365 nm irradiation (containing unstable-3 and stable-3) PSS 2:1

10. Eyring plot for thermal isomerization
By UV-Vis spectroscopy
Temp –93 to –53 oC
First order rate constants
Gibbs free energy 66 KJ/mol
From data half life of unstable isomer were calculated at room temp
70 ms

11. Conclusion…. 2 3
Changing the size of the aromatic upperhalf from a naphthalene moiety (as in 2) to a benzothiophene moiety (as in 3) leads to a dramatic acceleration in the thermal helix inversion.
The origin of this acceleration could be the reduction of the steric interactions between the upper- and lower-halves of the molecule in the fjord region
Thanking you