SINGLET OXYGEN PRODUCTION BY HYPERICIN IN VARIOUS SOLVENTS

The quantum yield of singlet oxygen production by hypericin was measur ed by means of an IR laser fluorimeter : Phi(Delta) = 0.37. 0.36, 0.26 , 0.17, 0.23, 0.23 and < 0.02 in methanol, ethanol, acetonitrile, acet one, dimethylformamide, tetrahydrofuran and D2O or H2O, respectively. The Phi(Delta) value decreases with the decrease of alpha the Taft's p arameter describing the ability of solvent to form hydrogen bonds with a solute. it was explained by the formation of the weak intramolecula r hydrogen bonds between CO groups and the nearest OH groups in hyperi cin, that should lead to the efficient radiationless deactivation of t he T-1 state by the mechanism of an intramolecular proton-transfer. I n water hypericin exists in the form of aggregates and the low Value o f Phi(Delta) can be explained by the low value of the triplet quantum yield for hypericin aggregates. The superoxide anion formation was not observed by pulsed conductivity method upon laser excitation of hyper icin aggregates in D2O and H2O and hypericin monomers in other solvent s investigated. Quantum yields of fluorescence are given.