Crystal structural change in poly(3-alkyl thiophene)s induced by iodine doping as studied by an organized combination of X-ray diffraction, infrared/Raman spectroscopy and computer simulation techniques

Preliminary results of the structural analysis of pristine and iodine-eloped poly(3-alkylthiophene)s [poly(3-hexylthiophene) and poly(3-dodecylthiophene)] have been recorded by utilizing an organized combination of X-ray imaging plate and computer simulation techniques. The crystal structure of the pristine polymers was found to be composed of stacked layers constructed by a side-by-side arrangement of alkyl groups, where both the single and double layer structures were possible. The iodine-doped poly(3-alkylthiophene)s have been found to possess a tunnel structure produced by a cooperative translation of the polymer chains along the chain axis by half the repeating period, into which polyiodide ions such as I-3(-) and I-5(-) were trapped to form a charge-transfer complex with polythiophene skeletal chains. These structural changes were simulated by constructing energetically minimized crystal structural models, which gave X-ray fibre diagrams close to those of the observed ones. The infrared and Raman spectra were found to change in two stages during iodine doping, and the possibility of polaron and bipolaron species constructed by a combination of polythiophene and iodine ions was proposed. (C) 1997 Elsevier Science Ltd.