GENERATION OF STABILIZED POLARONS AND BIPOLARONS ON EXTENDED MODEL THIOPHENE OLIGOMERS

A series of extended model thiophene oligomers (nT) have been oxidized in dilute solution by stoichiometric amounts of FeCl3. The respective radical cations nT+. (polarons) are quantitatively generated in the first step of the chemical process, as evidenced by in-situ optical absorption and ESR spectroscopies. The 6T+. radical cation salt of the hexamer precipitates as a highly stable, paramagnetic and conducting solid. In the second step of the oxidation, 6T+. is interconverted into the 6T++ dication (bipolaron). These unambiguous results, obtained on well-defined and non-interacting systems, are discussed in terms of discrete MO-levels and evidence the role of disorder and three-dimensional effects in the electronic properties of doped polythiophene.