Metallic state of polypryrrole: Effects of disorder

Recently synthesized polypyrrole (PPy) with greater crystallinity shows improved metallic properties. PPy doped with hexafluorophosphate (PF6) demonstrates a density of states at the Fermi level [N(EF)] comparible to doped polyaniline (PAN) and polyacetylene [(CH)x], as well as a plasma frequency in the dielectric responce (ϵ1) due to free Drude electrons in the far infrared. However, structural disorder strongly affects the metallic state. ϵ1 for PPy (PF6) also shows a second plasma frequency in the near IR due to localized conduction electrons, which provide a high conductivity at finite frequencies. Optical and magnetic measurements for more highly disordered PPy doped with p-toluenesulfonate (TsO) confirm the importance of structural order. Comparison of the optical response of PPy and PAN suggests that other interactions such as the steric interaction between rings also strongly affect the metallic state in doped polymers.