UV-vis and Raman spectroelectrochemical investigation of the redox behavior of poly(5-cyanoindole) in acidic aqueous solutions

Spectroelectrochemical properties of conducting poly(5-cyanoindole) films d eposited on indium tin oxide (ITO) and platinum electrodes are investigated using UV-vis and resonant Raman spectroscopies, The transitions from undop ed to semi-conducting state of P5CN require the partial oxidation of the po lymer to create radical-cations by insertion of charge-neutralizing anions into the polymer. In order to obtain detailed structural information from t he vibrational spectra, it is necessary to know the vibrational modes of ox idation-sensitive bands. Vibrational assignments were made on the basis of the results obtained on polyindole and P5CN in acetonitrile solution. The d rastic changes in optical absorption and Raman spectra observed at various stage of oxidation were explained by the conversions between at least three different structures. On the basis of the Raman spectra, we have identifie d the vibrational modes associated with neutral and polaronic segments. The perturbation associated with the coexistence of these polaronic segments h as been described as a quinoid structure growing on the expense of the benz oid one, The results obtained indicate that the molecular properties of the conducting polymers at various stages of an oxidation are better revealed by in-situ Raman spectra than by ex-situ studies. (C) 2000 Elsevier Science B.V. All rights reserved.