Geminate processes in the reaction of nitric oxide with 1-methylimidazole-iron(II) porphyrin complexes. Steric, solvent polarity, and viscosity effects

The quantum yields for photolysis of imidazole-iron(II) porphyrin-NO complexes have been determined in the following solvents: toluene, aqueous 1-methylimidazole, Nujol, and glycerol. The corresponding yields are 0.2, 0.077 (30% 1-methylimidazole in water), 0.064, and 0.007. Steric effects on NO photolysis were also investigated. The increasingly hindered porphyrins (mesoheme, anthracene-7,7-cyclophane heme, adamantane-6,6-cyclophane heme, and pyridine-5,5-cyclophane heme) had, in toluene, quantum yields of 0.21, 0.21, 0.29, and 0.49, respectively. Several conclusions are drawn from these results. (1) Polar solvents decrease NO quantum yields