Enhancing effect of amino acid residue models on the charge transfer in a Nafion® film incorporating Ru(bpy)32+ complex

Abstract

An ITO electrode was coated by a Nafion® film incorporating Ru(bpy) 3 2+ complex as a redox center. An amino acid residue model compound, either 3-methylindole as a tryptophan model, 4-methylimidazole as a histidine model, or p-cresol as a tyrosine model, was dispersed in the polymer matrix to study its effect on the charge transport by the complex with a potential-step chronoamperospectrometry (PSCAS) method from 0 to 1.3 V (vs. SCE). The results showed that the model compound increased the fraction of the Ru(bpy) 3 2+ which was electroactive, and this was ascribed most probably to the mediation effect of the model molecule on the charge hopping between the redox centers. Assuming a random distribution of the complex and the model molecule in the polymer matrix, the charge transfer distance by hopping was estimated to be 1.6 nm in the absence of a mediator, but a long-range charge transport distance was 2.2 nm in the presence of 3-methylindole, 2.0 nm in the presence of 4-methylimidazole, and 2.3 nm in the presence of p-cresol.