PHOTOINDUCED ELECTRON-TRANSFER BETWEEN CAROTENOIDS AND SOLVENT MOLECULES

EPR evidence for photoinduced electron transfer from beta-carotene and canthaxanthin to solvent molecules under 308-578 nm photolysis of fro zen carotenoid solutions in CCl4, CHCl3, CH2Cl2, and CS2 has been obta ined. The paramagnetic species are stable at 77 K and are attributed t o carotenoid radical cations (Car(.+)) and solvent derived radicals, F or a CS2 solution, solvent radicals are identified as CS2.- radical an ions, and for chlorinated solvents, they can be assigned to either a p redissociation species (R ... CI)(.-) or radical products R-.. The pro posed reaction mechanism includes energy and electron transfer from th e S-1 and S-2 excited singlet states of carotenoid molecules to the so lvent to form an intermediate donor-acceptor complex (1)[Car ... Sol] which decays yielding solvent-separated radical-ion pairs (Car(.+)... Sol ... Sol(.-)).