Electrical and Electrochemical Properties of Reduced, Oxidized, and Overoxidized Poly[2,5-di(-2-thienyl)-pyrrole] Films in Water/Acetonitrile Mixture

Poly[2,5-di(-2-thienyl)-pyrrole] [poly(SNS)] films up to 1.29 μm thick were anodically synthesized from a 5 mM monomer and 0.1 M solution at 0.50 mA cm −2 . These deposits with a large proportion of electroactive polarons compensated with dissolve upon reduction in this medium. Insoluble reduced films were synthesized in a (3:2 v/v) mixture with 0.1 M at −200 mV, having a small proportion of electroinactive charges trapped in polymer. Their cyclic voltammograms display an initial redox pair related to the reversible doping/undoping process with electroactive polarons, which can be continuously cycled from −200 to 340 mV. A further oxidation peak involves generation of bipolarons, while two subsequent overoxidation processes lead to polymer reticulation, without charge accumulation. Reduced films are then progressively oxidized from ca. 150 to ca. 600 mV and overoxidized between 660 and 1400 mV. The electrical conductivity rises upon oxidation, remaining almost constant during overoxidation. The impedance of reduced and oxidized forms decays with increasing film thickness and potential, although upon overoxidation, it increases as potential is shifted in the positive direction. All impedance measurements can be adequately simulated by a simple equivalent circuit. The calculated film capacitance for reduced and overoxidized forms is very low, and increasing values are found only as the polymer is gradually oxidized from ca. 150 to 500 mV. The high capacitances found for oxidized poly(SNS) indicate that it is adequate for charge-storage devices, although its use should be limited to potentials only involving its reversible doping/undoping cycling.