Evolution of Polaron States into Bipolarons in Polypyrrole

The kinetics of polaron recombination into bipolarons in polypyrrole has been studied by optical-absorption spectroscopy on films doped in situ in an electrochemical cell. ESR studies confirm that the metastable states possess spin, while the stable states do not. The data reveal a slow evolution, consistent with polaron-diffusion rates limited by the mobility of the accompanying counterion.