K. W. Willman

Viologen homopolymer, polymer mixture and polymer bilayer films on electrodes: Electropolymerization, electrolysis, spectroelectrochemistry, trace analysis and photoreduction

Two new viologen polymers are described and formed in films on Pt. Au. C and SnO2 electrodes. One polymer is based upon condensation of the organosilane monomer. N-methyl-N′-4-(2-trimethoxysilyl)-ethyl)-benzyl-4,4′ -bipyridinium (BVSi2+); the other upon the electropolymerization of the monomer 4-vinyl-4′-methyl-N,N′-ethylene-2,2′-bipyridinium (VDQ2+). Electrochemical properties of thin films of these polymers on electrodes are superior to films prepared from the monomer, N,N′-bis-4-(2-(trimethoxysilyl) -ethyl)-benzyl)-4,4′-bipyridinium. Spectroelectrochemical studies of films on SnO2 are used to illustrate optical and color changes accompanying electrode reactions, to demonstrate the extent of reactivity and to estimate the rate of charge transport in the film. Polymer mixtures of VDQ2+ with [Ru(vbpy)23+] can be prepared by simultaneous electropolymerization; sequential polymerization provides spatially segregated bilayers of these polymers, with consequent charge-trapping properties. The charge-trapping properties of the bilayers electrodes are applied to the analysis of trace dioxygen and to the accumulation of photoreduced viologen. Films of Poly-VDQ2+ and poly-BVSi2+ can be used to catalyze the reduction of dibromodiphenylethane.

Charge trapping reactions in bilayer electrodes

Abstract The cyclic voltammetric peaks for charging trapping and untrapping reactions between the inner and outer redox polymer films of five bilayer electrodes are compared to a theory for control of the rate of charge trapping by electron diffusion rates in the inner polymer film. The five bilayer electrodes use various different redox polymer films (electropolymerized poly-pyridine complexes of Fe, Ru, and Os, and polyvinylferrocene) arranged in different orders. The currents on the rising edge of the bilayer trapping and untrapping peaks follow the electron diffusion theory up to ca. 80% of the peak current; currents thereafter are controlled by another process(es). The analysis yields values for the electron diffusion constants in the inner bilayer polymer films, which agree with one another for different bilayers having the same inner film polymer films and which also agree with independent determinations by other methods. Two of the bilayers are made from the same two polymers, arranged in different inner-outer order. These bilayers also illustrate the occurrence of a “leak reaction”, in which charge trapped in the outer film is discharged via a thermodynamically unfavorable electron transfer reaction with the inner polymer film.