Fluorescence Property of Photochromic Diarylethenes with Indole Groups

Diarylethenes having a fluorescent indole ring as the aryl group 1a and 2a were synthesized. Upon alternate irradiation with 366 nm and visible ((lambda) > 480 nm) light, 1a underwent reversible photocyclization reactions to produce closed-ring isomer 1b. The fluorescence intensity also reversibly changed along with the reactions. The fluorescence quantum yields of the open-ring isomers 1a and 2a were 4.6 and 6.3% respectively, while the yields of the closed-ring isomers 1b and 2b were almost zero. The fluorescence quantum yields decreased with the increase in the photocyclization quantum yields.