Viologen(2+/1+) and Viologen(1+/0) Electron-Self-Exchange Reactions in a Redox Polymer

Article abstract of DOI:10.1021/j100169a056

A analysis is given of the electron-self-exchange reactions responsible for the steady-state redox conductivity of thin films of the electropolymerized monomer N,N'-bis(3-pyrrol-1-yl-propyl)-4,4'-bipyridinium tetrafluoroborate, sandwiched between two electrodes.Concentration-gradient-driven electron self-exchange in the liquid-acetonitrile-bathed viologen(2+/1+) mixed-valent state of this polymer, k_ex = 8 x 10³ M^-1 s^-1, is much slower than that for the viologen (1+/0) mixed valent-state, k_ex = 1.6 x 10⁵ M^-1 s^-1, which has a smaller activation barrier.Neither self-exchange reaction responds to use of alternative counterions except that both rates decrease in polymer containing tosylate counterions.The rate constant found for the electrical-gradient-driven viologen (1+/0) electron self-exchange, k_ex = 1.1 x 10⁵ M^-1 s^-1, observed in dry, N2-bathed polymer where ClO4(1-) counterion mobility is quenched, is nearly the same as the acetonitrile-bathed value.The rate constants appear to be dominated by characteristics of the polymer phase rather than the bathing environment of the polymer.Estimates are made of the counteranion diffusivity in acetonitrile-bathed films and of how it affects transient electron transport measurements.