Complexation of aliphatic amines with carbazole in the So and S1 states: Solvent effect on the deactivation of the excited complex Original Research Article

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 (Kg) 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 (kq): 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.