Photoinduced Shape Changes of Diarylethene Single Crystals:
Correlation between Shape Changes and Molecular Packing

　　Correlation between photoinduced shape changes of diarylethene single crystals and their molecular packing in the crystals was studied. The single crystal of 1,2-bis(5-ethyl-2-phenyl-4-thiazolyl)perfluorocyclopentene (1a) showed photoinduced deformation from square to lozenge similar as that of 1,2-bis-(2-ethyl-5-phenyl-3-thienyl) perfluorocyclopentene (2a). Although the two diarylethenes have different electronic structures and exhibit different colors upon UV irradiation, the crystallographic structures and molecular packing of the crystals are very similar each other. The result indicates that the deformation of bulk crystals is determined by the packing mode of component molecules in the crystal.