Excited-state triple proton transfer of 7-hydroxyquinoline along a hydrogen-bonded alcohol chain: vibrationally assisted proton tunneling

Proton relay in cyclic 7-hydroxyquinoline-(alcohol)2 complexes (see picture) has been explored in nonpolar solvents. The asymmetric triple proton transfer has an unusually large, temperature-independent, and viscosity-dependent kinetic isotope effect. Heavy-atom motions (wavy arrow) of solvent and bridging molecules allow proton tunneling by assisting the complex to reach the optimal precursor configuration. (Chemical Equation Presented)close454