Photocatalytic Reactions of Porphyrin-Based Multielectron Transfer Photosensitizers.

Individual metal centers assisted by redox-active ligands can serve as active sites for photocatalytic multielectron transfer (MET) substrate transformations. In porphyrin-based mononuclear systems, the primary steps of excitation and charge separation are mediated by the tetrapyrrole ligand acting both as photosensitizer and intermediate reservoir or for electrons. Accumulation and transfer of multiple redox equivalents requires a binding site that provides at least two stable oxidation states separated by more than one unit. The reversible photoconversion between low- and high-valent main group metalloporphyrins is described as an example of MET sensitization useful for artificial photosynthetic reaction schemes.