Design, Synthesis, Structure, and Spectroscopic and Electrochemical Properties of Phthalocyanines

The synthesis and spectroscopic and electrochemical properties of crown-ether substituted metallophthalocyanines (MCRPcs), optically active phthalocyanines (Pcs), subphthalocyanines (SubPcs), low symmetrical Pcs, ring-expanded Pcs, and novel oligomers of Pcs studied mainly by the author over the last 20 years have been reviewed, together with the electrocatalytic reduction of dioxygen using water soluble Pcs. MCRPcs form, on addition of certain kinds of cation, cofacial dimers through a two-step three-stage process. SubPcs react with isoindolediimines to produce mono-substituted Pc and Pc analogues. Optically active Pcs have been prepared to show the beauty and usefulness of circular dichroism spectroscopy. Ring-expanded or -shrunk and low symmetrical Pc analogues have helped in exploiting the relationship between size, symmetry, and spectroscopic and electrochemical properties of large aromatic molecules. Molecular orbital calculations on these compounds have succeeded in reproducing many of the experimental properties. New types of cofacial and planar dimers have been prepared, occasionally with a new concept. Water-soluble iron and cobalt Pcs electrocatalyze the reduction of dioxygen. When a four-electron reduction was attained, the reduction proceeded via hydrogen peroxide, and could be explained by a mechanism of electrochemical catalyst regeneration. The results for these compounds are occasionally compared with those of porphyrin systems.