Oxidative electropolymerization of 5-nitroindole

This report describes the electrochemical synthesis and properties of poly(5-nitroindole) films prepared on a bare platinum electrode. Cyclic voltammetry performed in acetonitrile solutions of 5-nitroindole (5 × 10−2 mol dm−3 and LiClO4 (0.15 mol dm−3) yields an oxidation wave at about 1.74 V versus SCE which corresponds to the formation of the 5-nitroindole radical cation. Potentiostatic deposition of the related polymer, poly(5-nitroindole), was carried out at a constant potential in the range 1.55–1.65 V versus SCE. The cyclic voltammogram of the resulting polymer in LiClO4 (0.15 mol dm−3)/acetonitrile is characterized by ill-defined anodic and cathodic peaks. When transferred to aqueous electrolytes, these films showed two reversible redox couples. The first reaction occurring at the less positive potential is pH independent and can be described as an electronic exchange only. The second redox transformation, at the most positive potential, is pH dependent and is related to both protonic and electronic exchanges between the polymer and the electrolytic solution. Another irreversible redox couple was observed for pH higher than 2.0 in aqueous solution containing Li cations. It can be related to n-type doping—undoping reactions of the polymer.