CONFIRMATION OF EXCITED-STATE PROTON-TRANSFER AND GROUND-STATE HETEROGENEITY IN HYPERICIN BY FLUORESCENCE UP-CONVERSION

Fluorescence upconversion measurements of hypericin and its methylated analog, O-hexamethoxyhypericin, which possesses no labile protons, co nfirm excited-state proton (or hydrogen atom) transfer as the primary photophysical event in hypericin. The presence of a rising component i n the time-resolved fluorescence of hypericin and the absence of such a component for the hexamethoxy analog are consistent with our assignm ent of excited-state proton or atom transfer as the primary photophysi cal process in the light-activated antiviral compound, hypericin. The results using the fluorescence upconversion technique, which detects o nly emission from the excited state, are in good agreement with our pr evious transient absorbance measurements. The results are also consist ent with a heterogeneous ground state of hypericin.