An organized combination of X-ray diffraction, infrared spectroscopy, and computer simulation in a study of crystal structural change in thermochromic phase transition of poly(3-alkyl thiophene)s

Crystal structural models of poly(3-alkylthiophene) have been proposed on the basis of X-ray diffraction, infrared spectra, and computer simulation. Four types of energetically possible models were extracted by energy minimization, among which the one-layered and double-layered structures consisted of parallel arrangements of non-interdigitated side-chain alkyl groups have been found to give excellent agreement with the observed X-ray diffraction pattern. The diffuse X-ray pattern of the high-temperature phase was also simulated by assuming a low degree of correlation between the neighboring chains due to the disordering in the side-chain conformation and relative position of polythiophene skeletals.