Charge transport and spin dynamics of chemically synthesized polypyrrole soluble in organic solvents

The results of the temperature dependence of dc conductivity, microwave dielectric constant, X-ray diffraction, EPR, and NMR experiments are reported for chemically synthesized polypyrrole films soluble in organic solvents. The temperature dependence of dc conductivity of these systems follows the three-dimensional variable range hopping model. The slope of the temperature dependence of dc conductivity varies with dopants and solvents used. Room temperature dc conductivities are in the range of ∼0.2-0.01 S/cm, and the localization lengths are estimated as ≤10 Å, which indicates a relatively strong localization of charge. The results of microwave dielectric constant experiments support the strong localization behavior. The X-ray diffraction studies show that soluble polypyrroles are amorphous. From electron paramagnetic resonance experiments, the density of states of polypyrrole doped with naphtha lenesulfonic acid in m-cresol solvent is estimated as ∼0.107 states/(eV ring). We obtain the result that the system achieves a more highly conducting state as the polarity of the solvent used increases.