QUENCHING RATE CONSTANTS IN AQUEOUS-SOLUTION - INFLUENCE OF THE HYDROPHOBIC EFFECT

The rate of quenching of aromatic hydrocarbon fluorescence by olefins is extremely dependent upon the solvent, being particularly fast in aqueous solutions. The possibility that this solvent effect is partly due to solvophobic interactions and/or to stabilization of a charge transfer intermediate is discussed. From an analysis of results obtained in several polar solvents, as well as from the effect of temperature and the addition of solutes with ''salting-in'' and ''salting-out'' capacities, it is concluded that the data in aqueous solution are better interpreted in terms of the stabilization afforded to the intermediate stages of the process by a hydrophobic effect arising from the decrease in water-solute interfacial area along the reaction coordinate.