In situ EPR spectroelectrochemical studies of paramagnetic centres in poly(3,4-ethylenedioxythiophene) (PEDOT) and poly(3,4-butylenedioxythiophene) (PBuDOT) films

In situ EPR spectroelectrochemical studies of two members of poly(3,4-alkylenedioxythiophene) family of polymers, namely poly(3,4-ethylenedioxythiophene)-PEDOT and poly(3,4-butylenedioxythiophene)-PBuDOT have been performed with an aim to investigate the effect of doping and subsequent dedoping on charge carriers in these polymers. The objectives of investigations were to characterise the type of paramagnetic centres appearing in the polymer and to observe the influence of doping on their concentration and other spectroscopic properties. It was found that the evolution of spins in both polymers upon doping follows a trend similar to that observed for other thiophene-based polymers. The characteristic points of these curves are different however for each polymer. The maximum spin concentration in PEDOT takes place at 0.2 V and for PBuDOT it is at 0.35 V. While generally similar in behaviour during doping. the behaviour of these two polymers upon dedoping is markedly different. For PBuDOT the concentration of spills follows a more or less reverse path of the doping curve whereas in PEDOT a hysteresis of concentration of spins appears. Similar trends are observed for the signals' DeltaB(pp) widths. Both polymers display distinct narrow EPR lines at the end of the reduction half-cycle suggesting that a noteworthy concentration of spins exist in them even in the fully reduced (dedoped) state. Analysis of the EPR spectra of the polymers in their doped states revealed their complex character. It was found that these complex spectra could be decomposed into two separate components-one Gaussian and one Lorentzian. Based on EPR microwave saturation studies the Gaussian component was attributed to highly mobile polarons which are confined in isolated spin packets and the Lorentzian one to delocalised less mobile polarons, homogeneously distributed within the material, which thus could be associated with the electrons of conductivity. (C) 2003 Elsevier Science B.V. All rights reserved.