Charge and Size Dopant Effects on the Conductivity of Poly‐3 Methylthiophene: An EXAFS Study

Large variations in the doping level and in the conductivity of poly‐3 methylthiophene electrochemically doped with metallic anions are observed, which are not expected from the electrochemical characteristics. Extended x‐ray absorption fine structure (EXAFS) spectroscopy has been used to determine the origin of these modifications. From a detailed study of the Au, Pt, and Ir absorption edge, information about the chemical state of Au, Pt, and Ir has been obtained, and the local structural geometry around the atoms has been determined. These studies reveal that no modification in the oxidation state and in the local environment of Au and Pt atoms in the and doped poly‐3 is observed, compared to the corresponding salts. In contrast, the environment of the Ir and Pt atoms in the and doped is modified: low chlorine atom number (from 6 in the salt to 4.49 in and 2.84 in ) and appearance of oxygen atoms in the first shell. The total atom number (4.43) surrounding the Pt atom and the near‐edge absorption spectra indicate that the oxidation state and the structure of the ion are not preserved in the system. The EXAFS results suggest that the charge of the anion is not an important factor for the doping process (same conductivity with and ) but the size of the dopant appears to be predominant (low conductivity with the large spherical ion).