Optical and electrochemical properties of a series of monosilanylene-oligothienylene copolymers in solution

Chemical and electrochemical oxidation of a series of copolymers consisting of a repeat unit of monosilanylene and oligothienylene (PSnT, n = 5-9, n denotes the ring number of an oligothienylene unit) is studied at room temperature. It is found that the oligothienylene unit of each copolymer is oxidized in the first oxidation step to cation radicals in equilibrium with pi-dimers, and in the subsequent step to dications. Energies of all absorption bands for these oxidized species and oxidation peak potentials for PSnT in solution scale linearly with the inverse of the size of the oligothienylene unit. The formation of pi-dimers is found to be favored by extension of the oligothienylene unit in PSnT. The equilibrium constant for the formation of pi-dimers for PS5T is evaluated as 5 x 10(4) M-1.