An electron paramagnetic resonance study of morphological disorder in polypyrrole through oxygen effects

Three samples of PF6 doped polypyrrole, which were measured to have dc conductivity of 400, 200, and 80 S/cm, were electrochemically obtained at temperatures of −40, 0, and 20 °C, respectively. The density of states at the Fermi level, obtained from EPR measurements, was found to be 0.86 states/eV ring for the most conducting sample, 0.31 states/eV ring for the least conducting sample, and 0.62 states/eV ring for the sample with a conductivity of 200 S/cm. EPR experiments were further performed using oxygen as a paramagnetic probe. We found that oxygen gas increased the asymmetry ratio (A/B) for the −40 °C sample, decreased A/B (after an initial increase) for the 0 °C sample, and had no effect on A/B for the 20 °C sample. The number of spins decreased on exposing the samples to oxygen, but the number returned toward the starting value on pumping the samples under vacuum. Combined with the EPR linewidth behavior, the results support inhomogeneous disorder model for these materials.