ELECTROCHEMICAL PROPERTIES OF POLYINDOLE AND POLY(5-CYANOINDOLE) IN LICLO4-ACETONITRILE AND IN HCL AND HCLO4 SOLUTIONS

Electropolymerization of indole and 5-cyanoindole leads to the formati on of electroactive polymer films. Their analysis by FT-IR spectroscop y, as a function of the oxidation potential in aprotic medium (LiClO4- acetonitrile) shows that they exhibit the same type of redox reactions . The coupling between the monomer units occurs in both cases between the C-2 and C-3 positions. On the contrary, when polyindole and poly(5 -cyanoindole) are cycled in HCl or HClO4 solutions, differences appear in their electrochemical behaviour. Two types of redox reversible pro cesses are observed in both polymers. For polyindole, these transforma tions are pH independent. For poly(5-cyanoindole), the reaction occurr ing at the most positive potential is pH dependent and is related to b oth protonic and electronic exchanges between the polymer and the elec trolytic solution. The other redox transformation, at less positive po tential, is pH independent and can be described as an electronic excha nge only. Mechanisms describing these two redox reversible reactions o ccurring when poly(5-cyanoindole) is cycled in acid solutions are prop osed. (C) 1998 Elsevier Science S.A. All rights reserved.