Conducting polymers from anodic coupling of dithienylacetylenes. Electrochemistry and potential-driven conductive and magnetic properties

Anodic coupling of dithienylacetylene and dithienylacetylenes substituted with alkyl and alkoxy groups has been investigated in acetonitrile. The resulting polymers have been characterized by cyclic voltammetry, UV-Vis spectroscopy, electrochemical quartz crystal microbalance, in situ ESR and in situ conductivity. The degree of conjugation of the polymers is increased as the monomer oxidation potential is lowered, which occurs with alkyl-substitution and even more with alkoxy-substitution. Alkoxy-substitution in position 3 of the thiophene ring produces the dimer, whereas 4-substitution yields an extensively crosslinked polymer. A regularly coupled polymer is obtained by 3,4-disubstitution with the ethylenedioxy group. The low conductivity (1 × 10−3 S cm−1) and the high unpaired spin density in the oxidized state of this polymer are explained by localization of charge and spin operated in the dithienyl moieties by the triple bonds.