A SPECTROSCOPIC STUDY OF THE HYDROGEN-BONDING AND PI-PI 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 exc ited singlet states of harmane (1-methyl-9H-pyrido/3,4-b/indole) with quinoline has been carried out in cyclohexane, toluene, and buffered p H = 8.7 aqueous solutions. To analyze how the number of rings in the s ubstrate influences these interactions, pyridine and phenanthridine ha ve 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 benzopy ridines and the solvent polarity increase hydrogen-bonding interaction s weaken and pi-pi van der Waals interactions become apparent. (C) 199 8 John Wiley & Sons, Inc.