Electrochemical Polymerization of Amino-, Pyrrole-, and Hydroxy-Substituted Tetraphenylporphyrins

The electrochemical polymerizations of tetrakis(o-, m-, and p-aminophenyl)porphyrin, tetrakis(p-(dimethylamino)phenyl)porphyrin, tetrakis(p-hydroxyphenyl)porphyrin, and tetrakis(p-N-pyrrolylphenyl)porphyrin and their nickel and cobalt metalated complexes are described. Oxidations of these monomers lead to thin polymeric coatings on electrodes by coupling reactions analogous to those operative in polyaniline, polypyrrole, and polyphenol electropolymerization. The films contain from two to several hundred layers of porphyrin sites and display reductive electrochemical and electronic spectroscopic properties similar to those of monomer solutions in acetonitrile or methylene chloride. The pyrrolyl- and amino-based polymers are polycationic and thus anion exchangers, whereas the hydroxy-based polymers (at pH > 8) are polyanionic. Films prepared from electropolymerization of cobalt tetrakis(o-aminophenyl)porphyrin display a split Co(III/II) wave in aqueous acid and base and are good oxygen reduction catalysts, whereas films prepared from all other cobalt porphyrin monomers display only one Co(III/II) wave and are poor catalysts.