Solid state electron-hopping transport and frozen concentration gradients in a mixed valent viologen-tetraethylene oxide copolymer

This paper describes electrochemistry and electron-hopping dynamics for a novel viologen-based redox polymer (poly-V2+) formed from the copolymerization of tetraethylene glycol di-p-tosylate and 4,4'-bipyridine. Current-potential responses and electron-hopping (i.e., self-exchange) rates have been measured for mixed valent films of poly-V2+ on interdigitated array electrodes contacted by tetrahydrofuran/acetonitrile/tetrabutylam-monium perchlorate electrolyte solution and as dry mixed valent films in vacuum or dry nitrogen. Electron transfer rates vary with the mixed valency composition of poly-V-2+/+ films (judging film composition from the electrolysis potential with the Nernst equation) according to bimolecular reaction theory for solvent-wetted but less well for dry films. Current-potential characteristics are also reported for mixed valent films that contain concentration gradients of the poly-V2+ and poly-V+ redox states, which we attempt to freeze into place by drying the film under a gradient-generating potential bias so as to immobilize the film's counterions. Current transients at room and reduced (-30 degrees C) temperature show that the room-temperature responses of films containing concentration gradients are sensitive to small changes in poly-V-2+/+ oxidation state at the electrode/polymer interfaces.