Liquid crystal character controlled by complementary discotic molecules mixtures: Columnar stacking type and mesophase temperature range

In this work, the mesophase properties were tuned via mixing two discotic molecules with structural complementarity. Compared with the liquid crystalline hexakis(n-hexyloxy)triphenylene (H6TP) materials (columnar hexagonal phase from 53 °C to 91 °C), mesophase types as well as phase transition temperatures varied with the introduction of crystalline hexaazatriphenylene derivative (PBH) molecules. The introduction of less than 33% amount of PBH disrupted the columnar hexagonal phase formed by H6TP remarkably, followed by the decreased clearing temperatures of liquid crystals. As the PBH amount was further increased, the destroyed columnar hexagonal phase was turned into the columnar rectangular phase, in which H6TP and PBH molecules together formed the columnar mesophase. The formation of new mesophase contributed to the enlarged mesophase temperature (from 44 °C to 144 °C). We speculated that the alkyl chains interaction induced by the PBH component competed with the strong π–π stacking between H6TP molecules, thus altering the liquid crystalline properties including mesophase types and phase transition temperatures.

By blending H6TP with PBH molecules, the stacking structures altered from the Colh phase to the Colr phase as the molar ratio of PBH raises, leading to the novel trend that the clearing temperatures firstly declined from 91 °C to 59 °C and then rose up to 144 °C with the increase of PBH content.Figure optionsDownload as PowerPoint slide