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) w as examined by the nanosecond laser photolysis and normal time scale analys is. The results showed that the thienyl group could stabilize the colored f orms as compared with the phenyl group and both singlet and triplet states were involved in the formation of the colored forms.