Ion Modulated Electroactivity in Thin-Film Polymers Derived from Bipyridyl and Phenanthroline Complexes of Iron
NORTHWESTERN UNIV EVANSTON IL DEPT OF CHEMISTRY
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Profound changes in the metal-centered electroactivity of thin-film redox polymerelectrolyte systems accompany the replacement of a conventional electrolyte solution aqueous tetraethylammonium perchlorate by any of several aq. CH3CH2SO3-Na solutions. For example for a poly-Fe4-methyl-4-vinyl-2, 2-bipyridine3m film in contact with an aq. sodium decanesulfonate solution a the overall redox capacity decreases by roughly half an order of magnitude, b the rate of hopping-based electron transport during charging decreases by 20-fold, and c the thermodynamic potential for metallopolymer oxidation moves to a significantly less positive value, in comparison to films equilibrated with conventional solutions. Further experiments show that the modulation behavior is associated with the uptake and release of charge-compensating anions during film oxidation and reduction i.e. cations are excluded, that the degree of modulation increases with increasing counter anion size, and that the modulation phenomenon is chemically reversible. These unusual effects are tentatively attributed to polymer-based steric constraints on large alkanesulfonate ion incorporation, together with hydrophobic partitioning effects. These factors apparently conspire to couple film-based electron motion strongly to counter- anion motion. Finally, spectroelectrochemical measurements show that CH3CH2 9SO3-containing-films are reversibly confined to a predominantly mixed-valent form FeIIFeIII, even at electrochemical potentials for removed from the formal potential for redox processes in the film.
- Physical Chemistry
- Polymer Chemistry
- Electricity and Magnetism