Crystal Structural Change of Poly(3-Alkylthiophene) Induced by Iodine Doping as Revealed by X-Ray Diffraction and Infrared/Raman Spectroscopic Measurements*

Abstract
Based on the X-ray fiber diagram, polarized infrared and Raman spectra, the crystal structural model of iodine-doped poly(3-alkylthiophene) has been proposed: polythiophene chains are displaced along the chain axis to give the tunnels extending along the b axis, in which the I- 5 ions are mainly intercalated. The resultant charge transfer between thiophene rings and iodine molecules is considered to give polaron and bipolaron with intense transition dipole moments along the chain axis, as judged from the infrared dichroism.