Time-resolved resonance Raman evidence for the exciplex formation of free-base porphyrin with an electron acceptor

Pump/probe time-resolved resonance Raman experiments (TR3) on free-base tetraphenylporphyrin (H2TPP) in benzene and benzene plus CCl4 mixed solvents were carried out to probe the mechanistic details and transient species involved in the photooxidation of H2TPP. We have detected spectral features due to the π-radical cation, and exciplex transient species in the singlet and triplet excited states at different timescales in the presence of CCl4 under laser irradiation. A mechanism for the photooxidation of porphyrins is discussed.