Electrochromic Polymers Covalently Anchored to Electrode Surfaces. Optical and Electrochemical Properties of a Viologen‐Based Polymer

Abstract

Smooth Pt and optically transparent electrodes can be functionalized with redox active polymeric material derived from the hydrolytically unstable {N,N'‐bis[‐3‐(trimethoxysilyl)propyl]‐4,4'‐bipyridinium}dibromide, I. The redox polymer on the surface is reversibly reducible to in either , and in the reduction of to is reversible. The vs. SCE, and vs. SCE in and , respectively. The vs. SCE in . The optical properties of (colorless), . (purple, , ), and (yellow, , ) depend somewhat on solvent/electrolyte. The optical spectral features associated with the three redox states of the surface polymer are easily distinguishable with the naked eye for coverages corresponding to >10−8mol/cm2 of redox active centers. Electrodes bearing are very rugged and do not deteriorate upon repeated cycling between and . Potential step/chronoamperometry experiments establish that the current for oxidation/reduction of the polymer is nearly proportional to , indicating that the rate of oxidation or reduction is controlled by a diffusion process with a diffusion constant, , of 10−9 to 10−10 cm2/sec depending on electrolyte and its concentration. In practical terms a potential step from 0.0 to −0.80V vs. SCE results in ∼50% reduction of to in a time as short as at a coverage of .