Electrochemical and Optical Characterization of Poly (3-methylthiophene): Effects of Solvent, Anion, and Applied Potential

The electrochemical and optical properties of poly(3-methylthiophene) (PMeT) coatings on electrodes exposed to different electrolytes, solvents, redox species, and applied potential were investigated. Electroanalytical (cyclic voltammetry, chronoamperometry, chronocoulometry, electrode admittance) and spectrophotometric measurements show that the nature of the charge-compensating dopant anion, the solvent (acetonitrile vs. water), and the applied potential have a profound effect on charge transport through the film. The oxidation (doping) of PMeT films, in contrast to its reduction (un-doping), depends on the size of the dopants (BF4-, CIO4-, PF6-, and CF3SO3-). The film suffers irreversible loss of electrochemical activity, to varying degrees, in aqueous solutions with ions, such as PO43-, SO42-~, CH3COO-, and phthalate. Ion trapping and slow structural relaxation in the polymeric films introduce hysteresis in the electrochemical and optical data. The doping of the film and the structural relaxation time, associated with its oxidation and reduction, depend strongly on the solvent. The electrochemical activity of PMeT films, in the electronic insulative state, is found to display an unusual dependence on the solvent and the applied potential. The nature of the polymer-dopant and polymer-solvent interactions and the mechanism of charge transport in PMeT are discussed. copyright.