HYDROGEN-BONDING INTERACTIONS BETWEEN HARMANE AND PYRIDINE IN THE GROUND AND LOWEST EXCITED SINGLET-STATES

A spectroscopic (UV-visible, Fourier transform IR, steady-state and ti me-resolved fluorescence) study of hydrogen-bonding interactions betwe en harmane (1-methyl-9H-pyrido/3,4-b/indole) and pyridine in the groun d and lowest excited singlet state is reported, In low polar and weakl y or nonhydrogen-bonding solvents, such as cyclohexane, chloroform, ca rbon tetrachloride, toluene and benzene, the analysis of the spectrosc opic data indicates that harmane and pyridine form 1:1 stoichiometric hydrogen-bonded complexes in both the ground and singlet excited state s. The formation constants of the complexes are greater in the excited than in the ground state. Hydrogen-bonding interaction in the excited state is essential for the quenching of the fluorescence of harmane b y pyridine. The stabilities of the hydrogen-bonded complexes between h armane and pyridine diminish as the polarity and hydrogen-bonding abil ity of the solvent increase.