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 X 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.