Hydrogen‐Bonding Interactions between Harmane and Pyridine in the Ground and Lowest Excited Singlet States

Abstract

Abstract— A spectroscopic (UV‐visible, Fourier transform IR, steady‐state and time‐resolved fluorescence) study of hydrogen‐bonding interactions between harmane (1‐meth‐yl‐9H‐pyrido/3,4‐ b /indole) and pyridine in the ground and lowest excited singlet state is reported. In low polar and weakly or nonhydrogen‐bonding solvents, such as cy‐clohexane, chloroform, carbon tetrachloride, toluene and benzene, the analysis of the spectroscopic data indicates that harmane and pyridine form 1:1 stoichiometric hydrogen‐bonded complexes in both the ground and singlet excited states. 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 by pyridine. The stabilities of the hydrogen‐bonded complexes between harmane and pyridine diminish as the polarity and hydrogen‐bonding ability of the solvent increase.