Triphenylene-Based Room-Temperature Discotic Liquid Crystals: A New Class of Blue-Light-Emitting Materials with Long-Range Columnar Self-Assembly

Abstract

A straightforward synthesis of multialkynylbenzene-bridged triphenylene-based dyad systems (via flexible alkyl spacers) that self-organize into room-temperature columnar structures over a long range is reported. The compounds with spacer lengths (n) of 8 and 10 exhibit a columnar rectangular mesophase whereas a compound with n = 6 shows a columnar rectangular plastic phase. Interestingly, the later compound (n = 6) shows the formation of well-nucleated spherulites of about several hundred micrometers that suggest the existence of a long-range uniform self-assembly of columns. All of these compounds show blue luminescence in solution and in the thin-film state under long-wavelength (365 nm) UV light. These compounds fulfill the described demands such as long-range columnar self-assembly at room temperature, a good yield with high purity, and blue-light emitters under the neat condition for possible potential applications in semiconductor devices. They also match the criteria of facile processing from the isotropic state because of their low isotropization temperature. This new class of materials is promising, considering the emissive nature and stabilization of the columnar mesophase at ambient temperature.

Highly Resolved Morphology of Room‐Temperature Columnar Liquid Crystals Derived from Triphenylene and Multialkynylbenzene Using Reconstructed Electron Density Maps

“…Tetraalkynylbenzene‐bridged triphenylene derivatives (triads) consist of two triphenylene units (T) connected via tetraalkynylbenzene (M) unit by using flexible alkyl spacers. Three compounds of the T‐M‐T series were prepared with alkyl chain of lengths ( n ) 6, 8 and 10 . These compounds are named as compound C6, C8 and C10, respectively.…”

“…On the other‐hand, multialkynylbenzenes (M) are the most investigated system among the various discotic nematogens where the rotational freedom of ethynyl linkers avoid the stacking of the disks needed for the column formation and hence induce a N D phase . In order to have the desired LC structure and to work with hierarchical structure, dyads and triads of T and T/M/PE have been also explored . But the detailed structure of their self‐assembly is missing.…”

“…We have also reported that multialkynylbenzene‐bridged triphenylene‐based triad (T‐M‐T) system show columnar rectangular phase which was derived from manual indexing of the peaks obtained in the WAXS diffractogram. Because the obtained diffraction pattern was not well resolved, therefore, the analysis of the pattern doesn't give accurate symmetries and cell parameters and hence, the detailed structure of these systems was not reported . In this paper, we present the quantitative and complete self‐assembled structure of these T‐M and T‐M‐T systems.…”

Self‐Assembly of Azobenzene Derivatives into Organogels and Photoresponsive Liquid Crystals

“…Upon heating, there is ab road endothermic peak at about 75 8Ca nd 55 8Cf or Azo-2 and Azo-3 xerogels, respectively,i ndicatingt heir supramolecular polymer characteristics. [44][45][46][47] In contrast, Azo-3 displayed ad endritic texture at 176 8Cd uring the cooling procedure from the isotropic melting state. Both molecules exhibitedt hermotropicl iquid crystalline behaviors.…”

“…These spherulites can be demonstrated as Maltese crosses where the isogyres followed the extinction of the polarizer/analyze. [44][45][46][47] In contrast, Azo-3 displayed ad endritic texture at 176 8Cd uring the cooling procedure from the isotropic melting state.…”