The influence of the nature of the coordinated metal atom on the photoelectrochemical activity of thin films of tetrapyrrole compounds

摘要

The photopotentials and photocurrents of thin films of various metal derivatives of tetrapyrrole compounds (TPCs) were compared to determine the photoelectrochemical activity of organic TPC semiconductors. The high reliability and reproducibility of the results were provided by a small spread of the parameters of the pigmented electrodes studied, a large statistical sampling, and thorough selection of determining measurement conditions. The results obtained for the photoelectrochemical reduction of oxygen show that TPC complexes with transition metals are effective in dark catalysis, because the special structure of their d shells provides strong overlapping with acceptor orbitals and dark electron transfer with a change in the valence of metals. Covalent bonds with ligands and a high electron density on the central atom contribute to this effect. In complexes of constant-valence metals with ionic bonds, acceptor coordination and reduction likely occur on pyrrole rings. The effectiveness of photoreduction increases as the ionization potential of TPCs decreases and electron density on the periphery of molecules grows.