Electrochemical, magnetic, and electrical properties of α,ω-capped sexithiophene films.: 1.: Neutral-polaron and polaron-bipolaron conductivities

Thin solid films of 14 sexithiophenes variously substituted at the terminal alpha,omega-positions were electrochemically deposited on electrodes by anodic coupling of the corresponding half-capped terthiophenes. Sexithiophene films were investigated by cyclic voltammetry, EQCM, in situ ESR, and in situ conductivity. Reversible oxidation is composed by two separate one-electron steps, the first of which is split into two 0.5-electron steps for most 3,4-ethylenedioxy-substituted terthiophenes. ESR indicates strong magnetic dimerization for the one-electron oxidized species. Conductivity (in the range 10(-4)-10(-1) S cm(-1)) is redox type and develops at the neutral-cation (neutral - polaron) and cation-dication (polaron-bipolaron) levels with values 5-10 times higher for the latter. The influence of steric, electron donor-acceptor, and conjugative effects on conductivity was evaluated by a suitable choice of endcapping substituents.