VIOLOGEN(2+/1+) AND VIOLOGEN(1+/0) ELECTRON-SELF-EXCHANGE REACTIONS IN A REDOX POLYMER

An 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 10(3) M-1 s-1, is much slower than that for the viologen(1+/0) mixed-valent state, k(ex) = 1.6 x 10(5) M-1 s-1, which has a smaller activation barrier. Neither self-exchange reaction responds to use of alternative counteranions 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 10(5) M-1 s-1, observed in dry, N2-bathed polymer where ClO4- 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.