Electropolymerized Aniline Derivative Films Possessing Selective Electron-transfer Mediation Properties for the Redox Reaction of Dissolved Substrates

Abstract

The electrochemical oxidation of o-phenylenediamine and N-methylaniline on basal-plane pyrolytic graphite electrodes in an acidic solution led polymeric film-coating of the electrode surfaces. The resulting poly(o-phenylenediamine) (PPD) and poly(N-methylaniline) (PMA)films showed reversible redox responses in aqueous solutions containing supporting electrolyte only. The film thickness and the surface concentration of the redox active site in films were proportional to the amount of the charge passed to prepare the films by a controlledelectrolysis. The PMA and PPD-coated electrodes revealed the selectivity for the redox reaction of dissolved substrates: in the case of the PMA-coated electrode, the oxidation of [Fe(CN)₆]^4- and the reductions of [Fe(CN)₆]^3- and [Irl₆]^2- could be mediated by the PM A film, while the film did not mediate the oxidation of [Ru(CN)₆]^4- and the reduction of N, N'-dimethy1-4, 4'-bipyridinium (MV²⁺) and functioned as a permselective film, ; in the case of the PPD-coated electrode, the reductions of [Fe(CN)₆]^3- and [IrCl₆]^2- could be mediated by the PPD film, but the oxidations of [Fe(CN)₆]^4- and [Ru(CN)₆]^4- and the reduc tionof MV²⁺ were not mediated. It is thus demonstrated that the PPD and PMA films can fun ction as electron-transfer mediators for the oxidation and reduction of dissolved substrates only in a limited range of potential, where dissolved substrates can be thermodynamically oxidized or reduced by the oxidized or reduced form of PPD and PMA films and that the electrodes coated with these films possess the property of“redox diode”.