MECHANISMS OF FLUORESCENCE QUENCHING BY HYDROGEN-BONDING IN VARIOUS AZA AROMATICS

Two different mechanisms seem to be responsible for the fluorescence q uenching of pyridylindoles by alcohols and pyridine. In alcohols, phot oexcitation of a cyclic hydrogen-bonded complex may lead to a double p roton transfer which, in turn, stabilizes an intramolecular charge tra nsfer state. Fast non-radiative transition to the ground state may the n occur. In pyridine, which may form a hydrogen bond to the indole NH group, an electron transfer from pyridylindole to pyridine, leading to a non-fluorescent exciplex, may be the cause of the decrease in the f luorescence quantum yield.