Photochromic mechanism of heterofused benzopyran derivatives

The photochromic behavior of 2-phenyl-2-(thien-2-yl)-2H-benzo[b]furano[3,2-f]benzopyran (1) and 2,2-diphenyl-2H-benzo[b] furano[3,2-f]benzopyran (2) was examined by the nanosecond laser photolysis and normal time scale analysis. The results showed that the thienyl group could stabilize the colored forms as compared with the phenyl group and both singlet and triplet states were involved in the formation of the colored forms.