ENHANCING EFFECT OF AMINO-ACID RESIDUE MODELS ON THE CHARGE-TRANSFER IN A NAFION(R) FILM INCORPORATING RU(BPY)(3)(2+) COMPLEX

An ITO electrode was coated by a Nafion(R) 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 com plex with a potential-step chronoamperospectrometry (PSCAS) method fro m 0 to 1.3 V (vs. SCE). The results showed that the model compound inc reased 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 r andom distribution of the complex and the model molecule in the polyme r 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. (C) 1998 Elsevier Science S.A. All rights reserved.