DETERMINATION OF THE ELECTRONIC-STRUCTURE OF OLIGOFURANS AND EXTRAPOLATION TO POLYFURAN

Gas-phase ionization and attachment energy values of the first few oligomers of furan have been determined experimentally and by semiempirical calculations and extrapolated to polyfuran. A comparison with the corresponding data determined previously for thiophene analogues indicates that (ideal, gas-phase) polyfuran should behave like polythiophene toward p doping and show a lesser disposition toward n doping. Cyclic voltammetry data show that in solution the oxidation of furan derivatives occurs as easily as for the thiophene analogues, while reduction is slightly more difficult. MINDO/3 valence ionization and electron affinity values for a quinoid form derived from the trimers indicate that furan and thiophene derivatives have similar electronic structures. It appears, therefore, that the low values of electrical conductivity reported for p-doped polyfuran are likely due to solid-state disorder.