A combined experimental and theoretical study on the photochromism of aromatic anils Original Research Article

Dynamics of photochromism have been studied in anil compounds using femtosecond transient absorption and picosecond fluorescence spectroscopies. The experimental observations were compared with the theoretical results obtained from AM1–SCF calculations. Excited-state intramolecular proton transfer (ESIPT) and photochromic reaction were found to occur from the S1 state, whereas normal fluorescence appears from the second excited singlet state. The photochromic processes are seen to be very fast, occurring within a few hundred femtoseconds. The lifetime of the S2 state was observed to be relatively long. This slower decay from higher excited singlet state was explained on the basis of the mixed nature of electronic transition comprising this state and relatively weak S2→S1 internal conversion. Theoretical results predict the ESIPT state to be zwitterionic in character; however, the final product may be a mixture of zwitterionic and nonionic in nature.