Electrochemical properties of oligothienylene-oligosilanylene block copolymers: Influences of block sizes

The fundamental electrochemical properties of oligothienylene-oligosilanyle ne block copolymers, especially the influences of the block sizes, were stu died in acetonitrile. In electrochemical oxidation, films of the polymers c ontaining Si-Si bonds suffer more or less from decomposition and dissolutio n due to partial cleavage of the Si-Si bonds in the oligosilanylene units. Decomposition decreases as the oligosilanylene block size decreases, and is not observed with copolymers containing no Si-Si bond, that is, oligothien ylene-monosilanylene copolymers. The copolymer films can also be electroche mically anion doped. Cyclic voltammograms obtained at high scan rates gener ally exhibit a two-step oxidative doping process, though the second-step ox idation is hardly seen for polymers with smaller oligothienylene blocks. Th e potentials of the oxidative doping peaks show a cathodic shift as the oli gosilanylene block size increases because of the sigma-pi -interaction in t he polymer chains and the action of the oligosilanylene block as a spacer, both of which are favourable to the stabilization of the cations and dicati ons generated in the polymer chain.