This paper presents the results of a spectral (absorption and emission) and photophysical study of 6-aminocoumarin (6AC) in the solvents with which this molecule interacts only nonspecifically (n-alkanes, tetrachloromethane and 1-chloro-n-alkanes) and in nitriles. The strong effects of the solvents on the emission spectra, fluorescence quantum yield and lifetime of 6AC were observed. The results of the steady-state and time-resolved photophysical study suggest the presence of very fast nonradiative deactivation processes. It is concluded that besides fluorescence, the efficient S1-ICT → S0 internal conversion in nonpolar aprotic solvents arises from vibronic interactions between close-lying S1-ICT(π,π*) and S2(n,π*) states. Moreover, unexpectedly efficient triplet state formation occurs. In nitriles the intermolecular hydrogen-bonding interactions with solvent molecules also facilitate the nonradiative decay process involving the S1-exciplex.
