KINETICS OF TRIPLET OXIDATION OF METALLO‐PORPHYRIN COMPOUNDS TO THEIR CORRESPONDING RADICAL CATIONS

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.