P. A. Heiney, E. Fontes, W. H. de Jeu, A. Riera, P. Carroll, and A. B. Smith, III, J. de Physique 50, 461-483 (1989).
We have used X-ray diffraction to study the discotic mesophases Dhd and Dho and the low temperature crystalline K phase of hexa(hexylthio)triphenylene. The high-temperature liquid crystalline Dhd phase is composed of a two-dimensional triangular array of columns, with short range intracolumn order. The intermediate-temperature Dho phase consists of a triangular array of columns with periodic positional and incommensurate helical intracolumn order. Furthermore, a three-column superlattice is found, which may result from the frustration imposed by molecular interdigitation in triangular symmetry. We suggest that the Dhd->Dho transition is driven by the increase in hydrocarbon tail stiffness and length with decreasing temperature. The K phase is found to be monoclinic. The K->Dho transition can be accomplished by a relatively minor displacement of the molecules.