AN OXIDIZED OLIGOTHIOPHENE THAT FORMS PI-STACKS

A dimethoxyterthiophene, substituted in the terminal alpha-positions with thioacetate groups, was synthesized and characterized. It was studied using cyclic voltammetry, ESR and optical spectroscopy in water solvent. A stable cation radical was formed using anodic or potassium ferrocyanide oxidation. In water the cation radical was aggregated into pi-stacks, as signified by an optical conduction band in the NIR, shifts in the Vis pi-pi* bands and an anisotropic ESR signal. This is the first example of such oligothiophene pi-stacks. Evaporation of the water from an oxidized sample gave a black solid which had a four-point-probe conductivity as a pressed pellet of 10(-3) S cm(-1). Thus, oligothiophenes have been shown to provide molecular conductors and the possible importance of pi-stacks in polythiophenes has been reinforced.