Columnar mesophase from a new hybrid siloxane-triphenylene

Abstract

The design, the synthesis and the mesomorphic properties of a new disc-like mesogen based on a hexasubstituted triphenylene core terminated with pentamethyldisiloxane pendant groups are reported. The siloxane fragments were grafted to the six terminal olefinic branches of a triphenylene precursor by a Pt-catalysed hydrosilylation reaction. Both the hexaolefinic and the hexasiloxane derivatives are mesomorphic, showing a rectangular columnar (Col_R—p2gg) mesophase between 55 and 88 °C for the former, and a broad hexagonal (Col_H—p6mm) mesophase between ambient temperature and 125 °C for the latter. The liquid crystalline behaviour was investigated by means of differential scanning calorimetry, polarised-light optical microscopy, and X-ray diffractometry. The mesophase temperature range and stability were considerably extended for the hybrid compound with respect to the siloxane-free compound. This behaviour is explained on the basis of enhanced microsegregation between the chemically distinct constituent components of the molecule.