Steady-state and time-resolved spectroscopic studies of benzanilides

Steady-state and time-resolved spectroscopic studies of benzanilide (I) and N-methylbenzanilide (II) were performed at 298 and 77 K in various solvent s. The results indicate that benzanilide fluorescence in non-polar solvents at room temperature involves three independent modes of emission: F-1(LE) normal fluorescence from the initially excited state S-1(LE) with lambda(ma x)=320 nm, F-2'(PT) fluorescence from the proton transfer tautomer with lam bda(max)=468 nm, F-2"(CT) fluorescence from the species where intramolecula r charge transfer appears, with lambda(max)=510 nm. At 77 K in MCH a new fl uorescence band, F-ag, appears at lambda(max)=415 nm instead of the F-2'(PT ) and F-2"(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 r oom temperature and at 77 K, shows only two fluorescence modes, i.e., the n ormal 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, i n MCH solution.