CHARGE-TRANSPORT THROUGH OSMIUM-CONTAINING REDOX POLYMERS IN NITROPHENYL-BASED SOLVENTS - EFFECT OF SOLVENT SIZE

Most studies on osmium-containing redox polymers have been carried out in aqueous media. The rate of charge transport through the osmium-con taining redox polymer as a function of solvent properties has not been investigated. This paper reports studies of osmium-containing redox p olymers in five nitrophenyl-based solvents: nitrobenzene, 2-nitrotolue ne, 3-nitro-o-xylene, 2-nitrophenyl pentyl ether, and 2-nitrophenyl oc tyl ether. These solvents differ from solvents conventionally used for studying osmium-containing redox polymers, such as water and methanol , in that they have both high dipolarities and larger molecular sizes. Both chronoamperometry and cyclic voltammetry studies on those solven ts indicate that it is the solvent size rather than the solvent polari ty that determines the rate of charge transport through the osmium-con taining redox polymer. The larger the solvent size, the slower the cha rge transport. We also found that the type of counterion has a strong effect on the cyclic voltammetry of the osmium-containing redox polyme rs in nitrophenyl-based solvents. No cyclic voltammetry waves were obs erved when using tetraphenylborate-based supporting electrolyte. Charg e transport activation enthalpy-entropy compensation was observed for the redox reactions of the osmium-containing polymer in methanol, nitr obenzene, and 2-nitrotoluene. This suggests that the effect of solvent on the rate of charge transport is likely to involve ion pairing and the associated solvation and polymer rearrangements accompanying the m aking and breaking of the ion pairs.