Steady-state and Time-resolved Spectroscopic Studies of Benzanilides

Steady-state and time-resolved spectroscopic studies of benzanilide (I) and jV-methylbenzanilide (II) were performed at 298 and 77 K in various solvents. The results indicate that benzanilide fluorescence in non-polar solvents at room temperature involves three independent modes of emission: F1 (LE) normal fluorescence from the initially excited state S1 (LE) with λmax = 320 nm, F2´(PT) fluorescence from the proton transfer tautomer with λmax = 468 nm, F2″CT) fluorescence from the species where intramolecular charge transfer appears, with λmax = 510 nm. At 77 K in MCH a new fluorescence band, Fag, appears at λmax=415 nm instead of the F2(PT) and F2″CT) fluorescence. This new emission originates from benzanilide dipolar aggregates or cis-imidol dimers. The decay times of these emission modes are different. N-methylbenzanilide, dissolved in nonpopular and weakly polar solvents at room temperature and at 77 K, shows only two fluorescence modes, i.e., the normal and the charge-transfer emissions at 320 nm and 520 nm, respectively. The fluorescence is deactivated with two decay times, 30 ps and 2.05 ns, in MCH solution.