Fatigue resistant properties of photochromic dithienylethenes: by-product formation

Beside normal cyclization/ring-opening photochromic reactions, a side reaction to produce a photostable by-product took place when 1,2-bis(2-methyl-5-phenyl-3-thienyl)perfluorocyclopentene was irradiated in deaerated hexane with ultraviolet light.