Anion effects on conductivity of isomorphous polypyrrole. Charge pinning by nucleophilic anions

Anion dependence of conductivity in well-ordered polypyrrole tosylate deposits was determined by anion exchange in aqueous medium with several inorganic (NO₃⁻, ClO₄⁻, F⁻, Cl⁻, Br⁻, BF₄⁻, HSO₄⁻, OH⁻) and organic (CF₃COO⁻, CH₃COO⁻, CH₃CH₂COO⁻, PhCOO⁻, PhO⁻, p-CH₃---C₆H₄---SO₃⁻) anions. Conductivity was found to be high (80–100 S cm⁻¹) and almost independent of anion size and (for anions of strong acids) of anion type, but it decreased with increasing anion basicity (70 S cm⁻¹ for carboxylate, 25 S cm⁻¹ for phenoxide and 3 × 10⁻² S cm⁻¹ for hydroxide anion). Quenching of conductivity by nucleophilic anions is explained by pinning of positive charges in the polypyrrole backbone with a pinning energy as high as 0.4 eV for OH⁻, as determined by E⁰ shifts in the cyclic voltammograms of the polymer.