X-ray diffraction and optical studies of fractionalized regioregular poly(3-hexylthiophene)

We report results of structural and photoabsorption studies of regioregular polyhexylthiophene fractions of different backbone length. Polymer of longer chains have better planarity and higher degree of crystallinity. The vibrational structure in the optical spectrum is more clearly visible. Increase of conjugation length and decrease of the optical gap with increasing polymerization degree have been observed. Moreover, the evolution of the photoabsorption spectra as a function of external pressure is presented. The spectra red shift with increasing pressure. The largest shifts have been observed for sample of the longest chains. The results are interpreted in terms of the large interchain coupling induced by pressure.