Journal
CHEMISTRY-A EUROPEAN JOURNAL
Volume 22, Issue 23, Pages 7950-7958Publisher
WILEY-V C H VERLAG GMBH
DOI: 10.1002/chem.201505149
Keywords
azobenzenes; photoisomerization; photomechanical motion; twisting; UV/Vis spectroscopy
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Funding
- High-Tech Research Center (TWIns)
- Leading Graduate Program in Science and Engineering, Waseda University
- Grants-in-Aid for Scientific Research [16K12918] Funding Source: KAKEN
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The photomechanical motion of chiral crystals of trans-azobenzene derivatives with an (S)- and (R)-phenylethylamide group was investigated and compared with a racemic crystal. Changes in the UV/Vis absorption spectra of the powdered crystals before and after UV irradiation were measured by using an optical waveguide spectrometer, showing that the lifetime of the cis-to-trans thermal backisomerization of the chiral crystals was faster than that of the racemic crystals. Upon UV irradiation, a long plate-like chiral microcrystal bent away from the light source with a twisting motion. A square-like chiral microcrystal curled toward the light with some twisting. Reversible bending of a rod-like chiral microcrystal was repeatable over twenty-five cycles. In contrast, bending of a plate-like racemic microcrystal was small. A possible mechanism for the bending and twisting motion was discussed based on the optimized cis conformer determined by using calculations, showing that the bending motion with twisting is caused by elongation along the b axis and shrinkage along the a axis.
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