Using microelectrochemical techniques, our laboratory has explored selfexchange-based electron transport in a variety of mixed-valent polymeric media. The transport rate is measured as the electron diffusion coefficient, D,, or the self-exchange rate constant k,, . The basic variables for electron transport in mixed-valent polymer materials include: ( a ) the physical mobility of the counterions of the polymer that migrate due to electroneutrality requirements, ( b ) the physical diffusion coefficient, Dphy\, of the monomeric or polymeric oxidized and reduced molecular sites or ions relative to the rate of electron hopping or tunnelling between donor/acceptor pairs, ( c ) the observational timescale relative to these mobilities which provides the distinction between transient and steady-state experiments, and ( d ) the chemical environment of the polymer, whether dry and solvent-free or contacted by solvent vapour or liquid. Experimental strategies and results are presented for the measurement of rates of ion diffusion, D , , in N,-dry and solvent-wetted mixed valent polymers. I n a dry, mixed-valent osmium complex polymer, the electron-transport rate measured under steady-state conditions, where no ion transport occurs concurrently, is much faster than the diffusion rate of the ion as estimated in a transient electrolysis experiment. In a solvent-wetted osmium complex polymer, the electron-transport rate measured under transient conditions is much slower than that of the ion which was measured under steady-state conditions. These circumstances allow isolation of individual processes and are interpreted as giving electrontransport rates not strongly influenced by macroscopic ion-transport rates. Cyclic voltammetry of [Co(bpy),]*+ and of Li+TCNQ-in dry poly(ethy1ene oxide) polymer electrolyte solvents exhibits differing measured diffusion coefficients, Dapp, for the oxidation us. the reduction of each compound, reflecting the coupling of physical diffusion and electron self-exchange transport. Microdisc electrode voltammetry of solutions of a synthesized ferrocene mono-tagged poly(ethy1ene oxide) in a polymer solvent of comparable molecular weight gives Dapp values smaller than those for ferrocene monomer dissolved in the same polymer solvent. The Dapp in the former case measures the self-diffusion rate of a linear chain polymer within a linear chain polymer solvent. Measurability of this rate has implications for assumptions about diffusive mobility of redox molecules attached to polymer chains.
