ELECTRONIC-STRUCTURE OF MONOMERIC AND DIMERIC CATION RADICALS IN END-CAPPED OLIGOTHIOPHENES

A temperature-dependent spectroelectrochemical investigation was carri ed out on a series of end-capped oligothiophenes (ECnT, 1, n = 3-5) an d an alkyl-substituted derivative (EC5T5Br, 2). Due to the stability o f the oligomers in the various oxidation states, the corresponding opt ical transition energies could be determined by applying controlled el ectrolysis in a thin-layer cell. Dimeric cation radical formation was observed for all oligomers at low temperature (200-235 K). An inverse correlation was found between the chain length and the transition ener gies of each species. We propose a simple energy-level diagram which c an account for the spectroscopic data.