POLYTHIOPHENE PUZZLE - A PLAUSIBLE SOLUTION

Previous in situ spectroelectrochemical studies on the redox transform ation of poly(3-methylthiophene) have been completed by further electr ochemical, EQCM and in situ conductance measurements. In the case of t hicker films, the generally observed single, wide anodic voltammetric wave could be separated into two oxidation steps, which are not consec utive, but complementary processes. The mass vs. potential curve from the EQCM measurements also reflects the double pattern of the electron ic process. The virtual stoichiometric factor per electron of the anio n during the first oxidation is lower than 0.5, and it is close to 1 i n the second oxidation region. The experimentally obtained smaller val ues are explained by the parallel removal of solvent. The conductance vs. logarithm of charge curves at small sweep rate show no hysteresis. However, during the first oxidation step the film is nonconducting; i ts transformation to conducting film is coupled with the second oxidat ion step. On the basis of the experimental observations, a detailed me chanism of the redox transformation is suggested in which the roles of the solvated and nonsolvated parts of the neutral film are distinguis hed. The achievement of the quasi-metallic state is connected to a cap acitive process in which an intermediate of uncompensated charge is in volved. (C) 1998 Elsevier Science S.A.