Pulse radiolysis-induced fluorescence lifetime measurements of liquid p-dioxane and p-dioxane mixtures

Liquid rho-dioxane exhibits a fluorescence from an excited aggregated state and the wavelength maximum of the fluorescence shifts to longer wavelengths in the presence of polar solvents. The fluorescence lifetimes and yields of the rho-dioxane and perdeuterated rho-dioxane aggregates in the presence of water and of methanol were determined from fluorescence measurements in pulse radiolysis experiments. In the presence of water, the fluorescence lifetime of the rho-dioxane aggregate increases with water concentration to a near constant value at high water concentrations. In the presence of methanol, the fluorescence lifetime exhibits an initial decrease at low concentrations followed by an increase to a near constant value at high methanol concentrations. For both mixtures, the increase in the fluorescence lifetime is accompanied by an increase in the fluorescence yield. The results are interpreted in terms of the nature of the excited aggregated state of rho-dioxane in the liquid