期刊
JOURNAL OF PHOTOCHEMISTRY AND PHOTOBIOLOGY B-BIOLOGY
卷 64, 期 2-3, 页码 117-122出版社
ELSEVIER SCIENCE SA
DOI: 10.1016/S1011-1344(01)00226-3
关键词
sunscreens; BM-DBM; dibenzoylmethane; triplet states; triplet quenching; photodegradation
Kinetic UV-VIS absorption data following 355 and 266 nm nanosecond laser flash photolysis of 4-tert-butyl-4'-methoxydibenzoylmethane (BM-DBM) solutions is presented. The kinetics of the decay of the non-chelated enol (NCE) produced following 355 nm excitation of BM-DBM solutions are analysed in terms of mixed 1st- and 2nd-order kinetics. The temperature dependences of the component rate constants are unusual and both 1st- and 2nd-order components display negative activation energies, which are explained by invoking pre-equilibria. In addition, it is shown for the first time that 266 nm laser photolysis of BM-DBM solutions leads to formation of the triplet state of the keto (K) form with a lifetime of similar to 500 ns. Under these conditions the triplet state of the K form is quenched by oxygen. (C) 2001 Elsevier Science B.V. All rights reserved.
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