Electron Self-Exchange Rates in a Site-Dilutable Osmium Bipyridine Redox Polymer

摘要

The metal complexes (Os(vbpy)3)(2+) and (Zn(vbpy)3)(2+) have beenelectroreductively co-polymerized as 70 to 230 nm thick films in which the mole fraction of Os sites is varied from chi(sub Os) = 1.0 to 0.49. Current-potential data have been obtained from concentration-polarized, Os(2+/3+) mixed valent films sandwiched between two electrodes and bathed in liquid CH2C12, CH2C12 vapor, and dry N2. Electron transport data were also obtained for non-concentration-polarized films bathed in dry N2 and subjected to an electrical gradient. The electron self exchange rate constants (k(sub EX)) derived from the concentration gradient-based measurements are larger in liquid and vapor CH2C12 media than in dry N2 k(sub EX) values in dry N2 are the same whether obtained from concentration gradient measurements using a Fickian electron hopping theory or from electrical gradient-based measurements with analysis both by a modified Marcus relation and by a dispersive transport model due to Scher/Montrolli Pfister. All k(sub EX) values, however derived, drop much more sharply by 35 to 50-fold with decreasing fraction of Os sites chi(sub Os) than expected from simple bimolecular kinetic or static percolation models. The behavior of the copolymer kinetics is rationalized based on a dependence of activation barrier on Os site concentration and/or non-ideal aspects of the microscopic structure of the copolymer. jg.