Photochromic and fluorescent properties of bisfurylethene derivatives

Photochromic diarylethenes having furan units (1 and 3) were synthesized and their photochromic performances were compared with those having thiophene units. The cyclization quantum yields of both derivatives in hexane are similar. In contrast, the cycloreversion quantum yield of the derivative having furan units (1) is much larger than that having thiophene units (2) in hexane. The difference is attributed to the conformation of the closed-ring isomers. Although 2a and 4a do not show any fluorescence, 1a and 3a exhibit fluorescence. Photochromism in the single crystalline phase was also observed for 1 and 3. Upon irradiation with 313 nm light, the colorless crystals 1 and 3 changed to violet and yellow, respectively.