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 α,ω-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 end-capping substituents.