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

Abstract

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.

Strategies for promoting discotic nematic phases

“…Indeed, triphenylene-based discotic dimers linked by conformationally constrained bridging groups have been observed to form nematic phases. 24–27…”

“…Subsequent DSC heating scans exhibit only the Col r -isotropic transition at 200 °C; on cooling, peaks associated with the isotropic-nematic and nematic-Col r transitions are reproducibly observed at 198 °C and 192 °C, respectively. This isotropic-nematic-columnar phase sequence is potentially beneficial for processing well-aligned films; 27 slow cooling of highly ordered smectic liquid crystals from overlying nematic phases has been shown to significantly enhance semiconductor device performance. 35,36…”

“…Indeed, triphenylene-based discotic dimers linked by conformationally constrained bridging groups have been observed to form nematic phases. [24][25][26][27] Dimers dDBP (6,6), dDBP (10,10), dDBP (10,6), and dDBP(6,10) were prepared via Steglich esterification (Scheme 1), coupling previously reported carboxylic acids DBP-A(6) and DBP-A(10) 28 with the corresponding alcohols DBP-OH(6) and DBP-OH (10). DBP-OH (10) was synthesized in 85% yield using the conditions reported for DBP-OH(6), 29 from the condensation of the phenanthrene quinone (Q10) with 3,4-diaminophenol.…”

Benzopyrano‐Fused Phenanthridine‐Based Columnar Mesogens: Synthesis, Self‐organization and Charge‐Transport Properties

“…When we look back to the literature, compared to other classes of discotic mesogens, there are meager reports available on dimers consisting of disc‐shaped molecules. Usually, these dimers are composed of two identical cores tethered through a supple or rigid spacer, and the nature of spacer has a profound effect on the structure of mesophase [16–21] . The rigid spacer connecting two disc‐shaped molecules results in the formation of an elliptical mesogen, which can be considered an intermediate between a calamitic and a discotic mesogen.…”

“…Usually, these dimers are composed of two identical cores tethered through a supple or rigid spacer, and the nature of spacer has a profound effect on the structure of mesophase. [16][17][18][19][20][21] The rigid spacer connecting two disc-shaped molecules results in the formation of an elliptical mesogen, which can be considered an intermediate between a calamitic and a discotic mesogen. Such systems are found to self-assemble into various columnar as well as nematic mesophases.…”