Photochromic Reactions of Diarylethenes in Single Crystals with Intermolecular OH⋅⋅⋅N Hydrogen‐Bonding Networks

The crystal structures and photochromic performance of a single crystal of a diarylethene derivative possessing carboxyl groups, 1,2‐bis(5‐carboxyl‐2‐methyl‐3‐thienyl)perfluorocyclopentene ( 1 a ), and cocrystals of 1 a with 4,4′‐, 2,4′‐, and 2,2′‐bipyridines were examined. In crystal 1 a , a discrete cyclic structure was observed, in which four 1 a molecules are linked through hydrogen bonds between the carboxyl groups. In the homocrystal, photoreactive and photoinactive conformers of 1 a exist in the ratio of 1:1. In the cocrystals of 1 a with bipyridines, OH⋅⋅⋅N‐type hydrogen bonds between 1 a and pyridyl groups were formed, and all 1 a molecules are fixed in a photoreactive conformation. Both the homocrystal 1 a and the cocrystals showed photochromic performances, and color variation from bluish‐violet to cyan was observed, depending on the conformation of the packed diarylethene molecules.