In situ electron spin resonance and Raman spectroscopic studies of the electrochemical process of conducting polypyrrole films

The electrochemical redox properties of conducting polypyrrole (PPy) films coated on electrodes are investigated in aqueous solutions by use of the in situ techniques of electron spin resonance (ESR) and Raman spectroscopy. Comparisons between the experimental in situ ESR data and a theoretical kinetic prediction on the basis of the polaron-bipolaron model are presented. Their mutual agreement confirms, straightforwardly from electrochemical points of view, that the formation of a polaron and its transformation to a bipolaren are a function of applied potential, and the polaron can be stable species intermediate between the oxidized and the fully reduced states. It supports the suggestion that both the polaron and bipolaren are involved in charge transport of the polymer. In correlation with the ESR conclusion, the in situ Raman observations have provided an evidence about the structural change of PPy's carbon-carbon bonds associated with the formation and transformation of the neutral, polaron, and bipolaren states, which can be qualitatively compatible with related molecular orbital consideration based on an EHMO calculation.