Photochromic properties of diarylethene derivatives having benzofuran and benzothiophene rings based on regioisomers

Photochromic diarylethene regioisomers having benzothiophene and benzofuran rings were synthesized and their structures were confirmed by X-ray crystallography. The photochromic properties of these diarylethenes were examined in solution as well as in the single-crystalline phase. We found that a diarylethene having 3-methylbenzofuran (FR2) ring show photochromism upon irradiation with UV light. For bis(3-methylbenzofuran) (BFR2) derivatives, the absorption band of the closed-ring isomer was longer than that of the open-ring isomer. The closed-ring isomer of the diarylethene derivatives having one 2-methylbenzofuran (FR3) ring showed a high absorption coefficient (more than 104 dm(3) mol(-1) cm(-1)). Although the distance between two reactive carbon atoms was within 0.42 nm, some diarylethene derivatives showed no photochromic reactions in the single-crystalline phase. Diarylethene derivatives having one 2-methylbenzofuran (FR3) ring efficiently showed photochromism in the single-crystalline phase.