Investigation of charge carriers in poly(3,4-butylenedioxythiophene) (PBuDOT) by means of ESR spectroelectrochemistry

In situ ESR spectroelectrochemical studies of poly(3,4-butylenedioxythiophene) (PBuDOT) have been performed, in order to investigate more closely the species responsible for the conductivity of this polymer in the doped state. In the process of electrochemical doping of the polymer, ESR spectra at progressively changed potentials were recorded. Then the subsequent dedoping process was studied accordingly. The results reveal that PBuDOT's ESR spectroscopic properties are markedly different form its close relative, poly(3,4-etylenedioxythiophene) (PEDOT). Firstly, the potential dependence of the spin concentration displays a clear peak-shaped transient with a gradual decrease at higher oxidation potentials. Similar behaviour is seen for the DeltaB(pp) widths of the ESR signal, indicating that the type of interactions between paramagnetic centres is potential sensitive. The course of the reduction process of the polymer is more or less the reverse of the oxidation one, with only a slight hysteresis of the spin concentration and a barely discernible one of DeltaB(pp) widths being observed. In PBuDOT, as in PEDOT, distinct narrow ESR lines revealing a noteworthy spin concentration in the reduced state of the polymer have also been observed. The presence of these residual spins in the dedoped polymer may indicate that the dedoping process of this polymer is indeed a slow one. The presence of trace amounts of impurities or oxygen may hinder the dedoping process, especially for thicker films.