Photochromic Reaction of Diarylethenes Having Phenol Moiety as an Aryl Ring

Three types of diarylethenes having one phenol moiety as an aromatic unit were synthesized in order to control pH change upon irradiation with UV and visible light. Upon irradiation with 313 nm light, these open-ring isomers were transformed to thermally unstable colored isomers in methanol solution. During the storage of the photoirradiated diarylethene solutions in the dark for 10 min, the thermally unstable closed-ring isomers were converted to thermally stable keto isomers. The structures of these isomers were characterized by H-1-NMR and X-ray crystallography. The keto isomers were transformed to the initial phenol isomer upon irradiation with visible light. Additionally, we also found the formation of a novel photochromic diarylethene derivative having one keto group on the cyclopentane ring during UV irradiation. A pH change between the two isomers was observed in a mixture of ethanol and water.