Excited-state intermolecular proton transfer reaction of 6-hydroxyquinoline in protic polar medium

Steady state and time resolved characteristics of 6-hydroxyquinoline (6-HQ) in alcoholic solvents and in a mixture of solvent (methanol:water) are studied. In neat alcoholic solvents, 6-hydroxyquinoline (6-HQ) shows emission around 376 nm. The emission corresponds to normal species and shows a single exponential decay (1.45 ns). However, in methanol containing water, dual emission i.e., normal one at ∼376 nm and a large Stokes shifted emission at ∼570 nm is observed. In presence of small percentage of water the decay time shows a decreasing trend and at higher percentage of water (>10% in v) a clear departure from the single exponential is observed. The results are interpreted in terms of multiple proton transfer through methanol and water chain.