Complexation of aliphatic amines with carbazole in the S-0, and S-1 states: Solvent effect on the deactivation of the excited complex

A study of the H-bonding interaction between carbazole, in its ground-and first excited singlet state, with aliphatic and alicyclic amines in different solvents is reported. In the ground state, the complexation equilibrium constants (K-g) correlate with the hydrogen affinity of the amines not with their gas-phase basicity or their ionization potentials, The same trend was observed for the fluorescence quenching rate constants (k(q)): this indicates that the same type of interaction is operative in both states, Concomitant to the quenching of carbazole fluorescence, a new, red-shifted emission grows up. The nature of this emission depends on the solvent: in alcohols the decay is biexponential and the new emission is that of the carbazole anion, In polar aprotic solvents, like acetonitrile, a three-exponential function describes the fluorescence decay, indicating that two radiative channels are operative for the deactivation of the excited carbazole amine couple. (C) 1997 Elsevier Science B.V.