Department of Chemistry, The University of Tokyo, Komaba
○Jun Harada Mayuko Harakawa Keiichiro Ogawa

Cis-trans photoisomerization is one of the most important types of photoreactions, and innumerable studies on the subject have been carried out. The photoisomerization in the solid state, however, has generally been considered difficult to take place, and only limited number of studies has been reported. The nonoccurrence of the reaction in the solid state is believed to be due to the fact that the isomerization involves large changes in the molecular shape, which should be hindered in the crystalline lattice. In this study we succeeded in single-crystal X-ray diffraction analyses of the cis-trans photoisomerizations of small organic molecules in crystals. The structural changes accompanying the reactions were revealed to take place not to disturb the crystalline lattices and in volume-conserving manners. A bicycle-pedal motion, which is another type of volume-conserving molecular motion in crystals, will also be discussed.