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 laser photolysis. The energy of tripler hypericin is E-T = 13 350 cm(-1), and for accepters with E-T < 13 300 cm(-1) the observed energy transfer rate constant declines with increasing exothermicity. Quenching of tripler hypericin by amines in acetonitrile and electron accepters in DMSO occurs via electron transfer. Spectroscopic and kinetic properties and the quantum yield of hypericin radical ion formation were established. The rate constant profiles for electron transfer (in both directions) are consistent with an excited-state reaction occurring before electron transfer. The rate constant of the interaction of reduced hypericin with O-2 was estimated to be 3.8 x 10(8) M-1 s(-1) in acetonitrile.