Synthesis and Mesophase Properties of Triphenylene Dimers Linked through Linear and Bent Alkyne-Aryl-Alkyne Bridges

Nematic mesophase formation in disc-like systems remains relatively rare compared to higher-order columnar organisation, but it is observed in some rigid dimeric systems. Mesophase formation in rigid discotic dimers has been sequentially probed and is shown to be predictably controlled through structural choice of the bridge. Moderately bent bridges shorten the discogen separation and reduce conformational freedom. Severely bent dimers (1,2-phenylene bridge) show no mesophases but, as the angle is widened, columnar and nematic organisation becomes possible and progressively more favoured. The linear arrangement gives the most stable columnar mesophase and a narrow-range nematic mesophase.