Studies of dopant effects in poly(3,4-ethylenedioxythiophene) using Raman spectroscopy

Raman spectroscopy has been used to study the doping processes in poly(3,4-ethylenedioxythiophene) PEDOT prepared via conventional electrochemical methods. The initially doped PEDOT films resulting from the polymerization process were first dedoped before being further oxidized in different electrolyte solutions at a number of different potentials to generate polymer films doped with a variety of dopants with different doping levels. Raman spectra of these re-doped PEDOT films were recorded ex-situ in order to monitor the progress of the re-doping processes by observing the shifts in the positions of CC stretching vibrations. This has provided an understanding of the extent of conversion between PEDOT structures from the dedoped state to the highly doped state during electrochemical re-doping. It was discovered that the extent of conversion varies with the type of dopant incorporated in the polymer films, which suggests that the doping process depends also on the nature of the dopant. Factors such as the size, the structural complexity and the charge on the dopant are believed to have significant effects on the efficiency of the doping processes in PEDOT. A curve-fitting method was also applied to fit the symmetric C-alpha=C-beta stretching band and its neighboring bands, in order to calculate the ratio of the band intensities due to the neutral and the oxidized structures in PEDOT. The doping level can then be approximately estimated by substituting this ratio into a previously determined correlation equation. Copyright (C) 2006 John Wiley & Sons, Ltd.