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Resonance Raman and electronic absorption studies of iron protoporphyrin IX chloride (hemin) in non-ionic Triton X-100 micelle in the absence and presence of hindered imidazole (2-methylimidazole and 1,2-dimethylimidazole) and unhindered imidazole under various experimental conditions are reported. Hemin undergoes photoreduction at the metal center, both in the absence and presence of hindered imidazole, in anaerobic, alkaline and neutral pH conditions on photoexcitation by laser radiation at 441.6 and 457.9 nm. It is inferred from this study that only the monomer hemin encapsulated within the micelle under the alkaline pH conditions is photoreducible. The photoreduction of hemin in this micelle occurs from an electron transfer as a result of dissociation of coordinated hydroxyl ion to the iron atom in the photoexcited state, which may also involve the OH ! Fe charge transfer transition around 360 nm.

We report a resonance Raman study on free-base tetraphenylporphine (H 2 TPP) and its chemically prepared diacid dispersed in polymethylcyanoacrylate (PMCA). Photoexcitation of the neutral porphine by laser light leads irreversibly to the formation of the diacid, with the p-cation radical as intermediate species.Resonance Raman (RR) spectra of the diacid dispersed in the polymer obtained with 441.6 nm in the wavenumber region of 100-1650 cm −1 are recorded. Wavenumbers with other excitation lines are also reported for the diacid species. Some bands assigned to out-of-plane vibrational modes and forbidden under ideal D 2h symmetry are also observed in the resonance Raman spectra of the diacid. These bands arise from the out-of-plane distortions, which reduce the symmetry of the molecule. These findings are supported by the electronic absorption studies of the diacid in the polymer.

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