Overall redox switching characteristics of osmium-containing poly(4-vinylpyridine) films immersed in aqueous p-toluenesulphonic acid

Abstract

The electrochemical quartz crystal microbalance (EQCM) has been used to study overall ion and solvent transfers in surface-immobilized [Os(bipy) 2(PVP) 10Cl] + films exposed to aqueous p-toluenesulphonic acid solutions. Crystal impedance measurements were used to identify situations where the observed frequency response was dominated by changes in the viscoelastic characteristics of the films. Unfunctionalized pyridine moieties can be protonated (p K a app = 2.9 ± 0.1), leading to pH-dependent film properties. The characteristics of films at open circuit and accompanying Os(II)/Os(III) redox switching were studied. In both cases, viscoelastic effects are observed at low and high electrolyte concentrations; at very low and intermediate concentrations the Sauerbrey equation can be used to interpret the frequency response. Even when the layer is non-rigid, isotopic substitution experiments show that solvent transfer accompanies redox switching. The film thickness dependence of the frequency response to redox switching is greater when the films are exposed to aqueous p-toluenesulphonic acid than to perchloric acid.