Quenching of excited triplet state hypericin with energy acceptors and donors and acceptors of electrons

The quenching of the triplet state of hypericin by accepters of electronic energy and donors and accepters of electrons was studied by nanosecond lase r photolysis. The energy of tripler hypericin is E-T = 13 350 cm(-1), and f or accepters with E-T < 13 300 cm(-1) the observed energy transfer rate con stant declines with increasing exothermicity. Quenching of tripler hyperici n by amines in acetonitrile and electron accepters in DMSO occurs via elect ron transfer. Spectroscopic and kinetic properties and the quantum yield of hypericin radical ion formation were established. The rate constant profil es for electron transfer (in both directions) are consistent with an excite d-state reaction occurring before electron transfer. The rate constant of t he interaction of reduced hypericin with O-2 was estimated to be 3.8 x 10(8 ) M-1 s(-1) in acetonitrile.