QUENCHING OF SINGLET OXYGEN (1-DELTA-G) BY CAROTENOID DERIVATIVES - KINETIC-ANALYSIS BY NEAR-INFRARED LUMINESCENCE

We have evaluated the efficiency of singlet oxygen (O2 (1DELTA(g)) que nching by a series of carotenoid derivatives. The rate constants of si nglet oxygen quenching (k(q)) have been determined by monitoring the n ear-infrared (1 270 nm) luminescence of singlet oxygen, produced by ph otosensitization upon continuous excitation of the sensitizer. The kin etic analysis of the results shows that, with values of k(q) higher th an 10(10) L mol-1 s-1. rhodoxanthin, zeaxanthin and lutein in benzene quench singlet oxygen almost as efficiently as beta, beta-carotene and canthaxanthin. Substituents on the ring systems of the carotenoids (h ydroxyl, phenylseleno, oxime or sulfate groups) seem to have little in fluence on the quenching rate constants. In fact, the potential increa se of k(q) resulting from favorable electronic factors may be compensa ted by aggregation effects due to a decrease of solubility of the caro tenoid.