KINETICS OF TRIPLET OXIDATION OF METALLO-PORPHYRIN COMPOUNDS TO THEIR CORRESPONDING RADICAL CATIONS |
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| Authors: | W Potter G Levin |
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| Institution: | Department of Chemistry, State University of New York, College of Environmental Science and Forestry, Syracuse, NY 13210, U.S.A. |
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| Abstract: | Abstract— The kinetics of photooxidation of triplets of metalloporphyrin compounds to their corresponding radical cations was investigated. Zn-tetraphenyl porphyrin (ZnTPP) and Mg-tetraphenylpor-phyrin (MgTPP) triplets were oxidized by europium salt with rate constants of 4.8 × 105M-1s-1 and 2.1 × 106M-1s-1, respectively. The high rate constant of oxidation of MgTPP triplet might be related to the ground state oxidation potential, being 0.54 V (SCE) for the Mg complex and 0.71 (SCE) for the Zn complex.
The rate constant of oxidation of ZnTPP excited singlet is in the order of diffusion control, i.e. ˜ 1010M -1 s-1. Excitation of ferric, cupric, cobaltic, and vanadyl tetraphenylporphyrin did not result in a long-lived triplet state that would allow oxidation studies using flash photolysis. |
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