Photoreduction of ferric-tetraphenylporphyrin in oxygen-containing solvents revealed by resonance Raman and absorption spectroscopy

Photoreduction is observed for FeIII(TPP)Cl (TPP is tetraphenylporphyrin) in some oxygen (O)-containing solvents under anaerobic conditions using resonance Raman (RR) and absorption spectroscopy. This process is found to be initiated by visible light in the 390–450 nm region. The coincidence of RR and absorption spectra of photoinduced species and of chemically reduced ones reveals that the final product of photoreduction is the high-spin FeII(TPP)L complex, where L = THF (tetrahydrofuran), DMF (dimethyl formamide) or 1,4-dioxane. Such a photoreduction is not observed under anaerobic conditions for the FeIII(TPP)Cl complex in benzene, pyridine or CH2Cl2, nor in the abovementioned solvents under aerobic conditions. No photoreduction is observed for FeIII(OEP)Cl (OEP = octaethylporphyrin). A mechanism for the photoinduced phenomenon observed for FeIII(TPP)Cl in O-containing solvents under anaerobic conditions is proposed.