Photo-induced diacid products of octaethylporphyrin probed by resonance Raman and absorption techniques

Abstract

The photochemical formation of di- and monoacid derivatives of octaethylporphyrin in CH₂Cl₂ or CCl₄-N alcohol mixtures in the presence of p-benzoquinone (p-BQ) has been studied by resonance Raman and optical absorption techniques. The results clearly indicate that the solvent or co-solvent acts as the proton source in the reaction. Simultaneous presence of p-BQ and methanol is found to be essential for diacid formation in CCl₄, while methanol greatly inhibits the process in CH₂Cl₂ solvent. However, in the presence of excess methanol in CH₂Cl₂ and p-BQ, porphyrin monoacid is formed. A chain mechanism is proposed for the photon-induced formation of octaethylporphyrin diacid products.