Photochemistry of Iron-Porphyrin Complexes. Biomimetics and Catalysis

Abstract An intramolecular electron transfer can occur in iron porphyrin complexes that are irradiated with light of suitable wavelength corresponding to axial ligand-to-metal charge transfer transitions. This process leads to the reduction of Fe(III) to Fe(II) and to the oxidation of the axial ligand to a radical species. The efficiency of the photoredox process is increased in the presence of species able of trapping the ferrous complex and/or the radical in competition with the back electron transfer process. Photoredox reactions of iron porphyrins and heme-proteins (cytochrome c) are examined in the framework of the fundamental role of electron transfer processes in biological systems. The products of the primary photoprocess can induce reactions leading to reduction or oxidation of various substrates with catalytic efficiency. This biomimetic aspect of the photoredox behavior of iron porphyrins is pointed out examining the results obtained in investigations concerning the iron-porphyrin based photoreduction of CCl4 in homogeneous solution, and photooxygenation of alkanes in both homogeneous and heteterogeneous systems.