Studies on the photochromic mechanism of 1,2-dimethyl-5-phenyl-3-pyrryl succinic anhydride

Photochromism of 1,2-dimethyl-5-phenyl-3-pyrryl fulgide (compound I) has been investigated in various solvents. The photocyclization process of I has been examined by means of nanosecond time resolved absorption spectroscopy; a new transient species was found on the nanosecond time scale. Oxygen can severely quench the new transient species. The photocyclization process is shown to be complicated. Both the excited singlet state and the excited triplet state are involved in the photochromic process.