Photooxidation of cobalt(II)meso-tetraphenylporphyrin by p-benzoquinone and its mechanism studied by optical absorption and resonance Raman spectroscopies

Abstract

Laser excitation of Co II TPP within the Soret absorption band in the presence of pbenzoquinone (p-BQ) results in oxidation of the complex. Oxidation occurs both at the metal center and the porphyrin ring depending upon the experimental conditions. Under anaerobic conditions, oxidation takes place at the metal center to produce the cobaltic species Co III (TPP) + , while in the presence of molecular oxygen oxidation also occurs at the porphyrin ring giving Co III (TPP) 2+• cation radical as oxidation product. From the inhibiting effect of peroxy radical trapping agent on the photooxidation of Co II TPP under aerobic conditions, the two-electron oxidation is suggested to involve solvent radicals and we discuss the mechanistic details of the process in this work.