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 -V 2+ ) 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 -V 2+ on interdigitated array electrodes contacted by tetrahydrofuran/acetonitrile/tetrabutylammonium 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 -V 2+ 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 °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.