Crystal Structure of Poly(3-alkylthiophene) and Its Doping Effect

Crystal structure of poly(3-alkylthiophene) having various length of side chain ranging from 4 to 18 has been studied by X-ray diffraction measurement. The lattice parameters of rhombic structure of poly(3-alkylthiophene) were varied with alkyl chain length. Distance between main chains along the side alkyl chains increases with increasing alkyl chain length, while that between the neighboring π-conjugation planes on the main chains increases slightly with increasing alkyl chain length longer than dodecyl group. The lattice parameter was also varied upon electrochemical doping, indicating incorporation of dopant anion into the crystal region of poly(3-alkylthiophene).