Electrochemical anion doping of poly[(tetraethyldisilanylene) oligot 2,5-thienylene)] derivatives and their p-type semiconducting properties

Chemically synthesized poly[(tetraethyldisilanylene)oligo(2,5-thienylene)] derivatives (DS/mT; m = 3 to 5) have been successfully anion-doped by electrochemical oxidation. Band-gap energies of 2.52, 2.65, 2.82 and 3.27 eV were evaluated for DS5T, DS4T, DS3T and DS2T respectively. The DS5T, DS4T and DS3T films exhibited electrical conductivities of the order of 10^?3 to 10^?4 S cm^?1 when doped with BF₄^?. The work functions of the films changed from 5.1 to ca. 5.5 eV with electrochemical anion doping. In cyclic voltammograms of the polymer films for anion doping and dedoping, an anodic peak potential and a cathodic one (E_pc.) shifted to the positive direction as the number m of thienylene units decreased. E_pcs at a sweep rate of 100 mV s^?1 were about 0.8, 0.9 and 1.0V for DS5T, DS4T and DS3T respectively. Reversible electrochemical doping and dedoping of the DS5T film were feasible when the potential was cycled between 0 and 1.2 V. At potentials more positive than 1.2 V, however, both overoxidation of the oligo(thienylene) unit and Si-Si bond cleavage took place, leading to decreases in conductivity and work function of the film.