PHOTOCHEMISTRY OF IRON-PORPHYRIN COMPLEXES - BIOMIMETICS AND CATALYSIS

An intramolecular electron transfer can occur in iron porphyrin comple xes that are irradiated with light of suitable wavelength correspondin g to axial ligand-to-metal charge transfer transitions. This process l eads 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 p rocess is increased in the presence of species able of trapping the fe rrous complex and/or the radical in competition with the back electron transfer process. Photoredox reactions of iron porphyrins and heme-pr oteins (cytochrome c) are examined in the framework of the fundamental role of electron transfer processes in biological systems. The produc ts of the primary photoprocess can induce reactions leading to reducti on or oxidation of various substrates with catalytic efficiency. This biomimetic aspect of the photoredox behavior of iron porphyrins is poi nted out examining the results obtained in investigations concerning t he iron-porphyrin based photoreduction of CCl4 in homogeneous solution , and photooxygenation of alkanes in both homogeneous and heteterogene ous systems.