The mechanisms of photochromic transformations of 2-indolylfulgides

Photochromic properties of 2-indolylfulgides, namely, Z-3-[1-(1,3-dimethyl- 1H-indol-2-yl)ethylidene]-4-isopropylidenetetrahydrofun-2,5-dione and E-3-i sopropylidene-4-(1-methyl-1H-indol-2-ylmethylidene)tetrahydrofuran-2,5-dion e, were studied. The quantum yields of their photochemical isomerizations i n toluene and the rate constant of the dark ring-opening in ethanol were de termined. The fluorescence spectra of the open and cyclic forms of 2-indoly lfulgides were measured. It was assumed that the excited-state Z-isomer can be transformed into a cyclic isomer without intermediacy of an E-isomer in the ground state.