PHOTOPHYSICAL BEHAVIOUR OF 5-METHOXYPSORALEN IN DIOXANE-WATER MIXTURES

Abstract— Triplet-triplet absorption spectra, intersystem crossing quantum yields, fluorescence lifetimes, and fluorescence quantum yields of 5-methoxypsoralen (5MOP) in dioxane-water mixtures are reported. The fluorescence and triplet formation quantum yields depend strongly on the water content in the mixtures, increasing up to maximum values which are, respectively, twentyfold and fivefold larger than in dioxane and then decreasing. This behaviour is essentially due to the variation of the internal conversion rate constant. With these solvent mixtures it is possible to emulate the dielectric response of 5MOP photophysical parameters in other media, such as in biological model systems and in human blood lipoproteins. The biological importance of these results is discussed.