A spectroscopic study of the hydrogen bonding and π–π stacking interactions of harmane with quinoline

A spectroscopic (UV–vis, Fourier transform IR, steady state, and time-resolved fluorescence) study of the interactions of the ground and excited singlet states of harmane (1-methyl-9H-pyrido/3,4-b/indole) with quinoline has been carried out in cyclohexane, toluene, and buffered pH = 8.7 aqueous solutions. To analyze how the number of rings in the substrate influences these interactions, pyridine and phenanthridine have also been included in this study. In cyclohexane and toluene 1 : 1 stoichiometric hydrogen-bonded complexes are formed in both the ground and the excited singlet states. As the number of rings of the benzopyridines and the solvent polarity increase hydrogen-bonding interactions weaken and π–π van der Waals interactions become apparent. © 1998 John Wiley & Sons, Inc. Biospectroscopy 4: 185–195, 1998