Trigonal 1,3,4-Oxadiazole-Based Blue Emitting Liquid Crystals and Gels

Abstract

Star-shaped molecules consisting of a 1,3,4-oxadiazole core derivatized with alkoxy-substituted phenyl ethynylenes, FD12 (dodecyl) and FD16 (hexadecyl) were synthesized. These molecules exhibited enantiotropic columnar mesophases over a wide temperature range, with the liquid crystalline phases exhibiting strong blue fluorescence. On cooling, FD12 transformed into a transparent glass at room temperature wherein the liquid crystalline texture was retained. The glassy film remained stable over a period of one year and exhibited blue luminescence with an absolute quantum yield of 26%. The oxadiazole derivatives formed stable luminescent gels in decane and study of their morphology by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) indicated formation of interlocked network of self-assembled fibers. X-ray diffraction (XRD) analysis of the xerogel of these derivatives indicated oblique columnar ordering of the molecules within the fibers. The length of the alkyl substituent was observed to have a significant effect on the absorption and fluorescence properties of the gels, which was attributable to the role of the alkyl substituents in controlling the nature of the molecular packing within the self -assembled fibers of the gels.

Recent progress in luminescent liquid crystal materials: design, properties and application for linearly polarised emission

“…Highly polarised PL was observed in all LC phases, with the order parameters (S) of 0.46, 0.44, and 0.78 in the S X , S A , and N phases, respectively. 68 These star-shaped materials showed columnar mesophases and gelating properties. The homogeneously aligned film of 9 was obtained on a CuPc film prepared by epitaxial growth.…”

Synthetic Approaches to Star‐Shaped Molecules with 1,3,5‐Trisubstituted Aromatic Cores

“…Das and co‐workers reported the synthesis of star‐shaped molecules 336 a , b , which contained 1,3,5‐(1,3,4‐oxadiazolyl)‐substituted 1,3,5‐benzene moieties as core units and dialkoxyphenyl groups at their peripheries (Scheme ) . These compounds were found to exhibit strong blue fluorescence in their liquid crystalline phases and the alkyl chain length was responsible for the absorption and fluorescence properties of the gels, owing to the adoption of different molecular packing configurations.…”

“…Kim et al reportedt he synthesis of star-shaped molecule 95, which exhibited ad iscotic nematic phase, with 1,3,5-triethynyl-benzene as ac entral core and 2,5-diphenyloxadiazole side arms (Scheme29). [24] The parent C 3 -symmetrical molecule (93) was derived from 1,3,5-tribromobenzene (75). Treatment of 1,3,5-tribromobenzene (75)w ith trimethylsilylacetylene (92) and K 2 CO 3 produced 1,3,5-triethynylbenzene (93).…”

Some Features of Liquid Crystalline Oxadiazoles

“…24. Recently [25], star-shaped molecules consisting of a 1,3,4-oxadiazole core were synthesized. These molecules have columnar mesophases over a wide temperature range, where the mesophases exhibiting strong blue fluorescence.…”