STEADY-STATE AND TIME-RESOLVED SPECTROSCOPIC STUDIES OF ALPHA-NAPHTHANILIDES AND BETA-NAPHTHANILIDES

Using chemical substitution and polarity perturbation effects, three competitive fluorescence emissions from a common initial excited singlet state of alpha and beta-naphthanilide are observed in non-polar solvents at 298 K. The fluorescence emissions are assigned as the normal fluorescence from a locally excited state (S1(LE) --> S0), the proton-transfer tautomer emission (S'1(PT) --> S'0(PT)) and the intramolecular charge-transfer fluorescence (S"1(TICT) --> S0(FC)). The picosecond time-resolved absorption spectra confirm the presence of excited species in different electronic states, e.g. S1(LE) and S'1(PT) with comparable decay constants and S"1(TICT) and T1(LE) with larger decay constants. At 77 K, the luminescence spectra appear as normal fluorescence (for N-methyl-alpha-naphthanilide and N-methyl-beta-naphthanilide) or a fluorescence emission from microcrystals (for alpha- and beta-naphthanilide) and very strong phosphorescence emission.