Photophysical properties of betaxanthins: Vulgaxanthin I in aqueous and alcoholic solutions

Betaxanthins are yellow pigments present in Caryophyllales plants and some higher fungi. We characterize photophysical properties of vulgaxanthin I and extracts of Amanita muscaria L. Vulgaxanthin I photoexcitation at λexc=476 nm leads to the S1 excited state with the S1→Sn absorption bands at ca. 390 and 920 nm in both aqueous and alcoholic solutions. The S1 state lifetimes (2.9 and 37 ps in water) imply that vulgaxanthin I exists in two stereoisomeric forms. An increase in the solvent viscosity extends the S1 lifetimes and fluorescence quantum yields, probably due to hindered internal rotations in the dye. Internal conversion is the major S1 state deactivation path, with fluorescence being a minor channel, and S1→T1 intersystem crossing not observed. Betaxanthins extracted from A. muscaria L. have similar properties. Efficient dissipation of the absorbed light energy as heat supports the postulate of photoprotective role of betaxanthins in vivo.