Excited State Interactions of Protoporphyrin IX and Related Porphyrins with Molecular Oxygen in Solutions and in Organized Assemblies
We have studied the photooxidation of protoporphyrin IX and the related intermediates and products of its oxidation in homogeneous solution (mostly organic solvents) and in aqueous surfactant media, in particular, various micellar and vesicular media. Our contribution first discusses the reaction of protoporphyrin IX, the mono- and diformyl oxidation products, and the “green” hydroxyaldehydes formed from protoporphyrin IX. In solution, all of these compounds are good sensitizers for singlet oxygen; a small amount of the interaction of porphyrin excited states with molecular oxygen may result in electron transfer to give oxidized porphyrin (cation radicals) and superoxide anion. However, in most cases the singlet oxygen path is predominant. We have also measured the reactivity of the various porphyrin ground states with singlet oxygen. Our studies in organized assemblies show that reactivity may be quite different; studies still in progress are attempting to elucidate whether singlet oxygen remains the primary reactant in these processes. Preliminary results of quenching and sensitization studies in the organized media are discussed.
KeywordsMethylene Blue Molecular Oxygen Singlet Oxygen Organize Medium Methyl Viologen
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