Polymer solvent dynamic effects on an electron-transfer cross-reaction rate at a redox polymer/polymer solution interface

Abstract

Electron-transfer cross-reaction rate constants (k[sub 12]) for the oxidation of polyether solutions of [Fe(4,7-dimethyl-phenanthroline)[sub 3]][sup 2+] at a poly[Os(bpy)[sub 2]/(vpy)[sub 2]][sup 3+] redox polymer surface have been measured as a function of the polyether solvent employed. Previous measurements in monomer solvents produced values of k[sub 12] adherent to a theoretical model incorporating the monomer solvent longitudinal relaxation time ([tau][sub L]), dielectric constant, and the cross-reaction free energy. Values of k[sub 12] are smaller in polyether solvents, consistent with reaction rate control by solvent dipole relaxation times ([tau][sub L][prime]) that are longer in polymeric relative to monomeric solvents. Further, k[sub 12] decreases under conditions where polyether chain segment fluctuations are expected to be slowed, e.g., longer polyether chain length and increased LiClO[sub 4] and Zn(CF[sub 3]SO[sub 3])[sub 2] electrolyte concentrations. The diffusion coefficient of the iron complex in the polymer solution, for analogous reasons of slowed chain segmental mobility, also decreases in longer polyether chain solvents and at higher electrolyte concentrations. 30 refs., 6 figs., 3 tabs.