| Abstract: | The molecular geometries of neutral and dicationic oligomers comprising 7, 10, 13 and 16 rings of thiophene, furan and pyrrole were determined using quantum mechanical calculations. The usual benzenoid structure was characterized for neutral oligomers, whereas a quinoid structural defect which extends over six rings was found for dications. Analysis of the transition region, where the quinoid structure changes to the benzenoid one, revealed structural differences between thiophene, furan and pyrrole derivatives. |
