Tetrakis(oxadiazolylphenyl)pyrazines: New St. Andrew′s Cross‐Shaped Liquid Crystals

Abstract

Dedicated to Prof. Gerhard Wenz on the occasion of his retirementπ-Conjugated molecules with the shape of St. Andrew's cross have been synthesized via fourfold Huisgen reaction. Four 2,5diaryl-1,3,4-oxadiazol arms are attached to a central pyrazine nucleus. These fluorescent stars, when decorated with a rim of eight alkoxy side chains are discotic liquid crystals. Depending on the substitution pattern, the width of the liquid phase varies within a broad range of 25°C to 250°C. In their liquid crystalline phase, the molecules assemble in a typical hexagonal columnar supramolecular arrangement.

Tris(5‐aryl‐1,3,4‐oxadiazolyl)benzotrithiophenes – Discotic Liquid Crystals with Enormous Mesophase Ranges

“…Alkoxyaryltetrazoles, the counterparts for the Huisgen reaction, are successfully prepared by two different synthetic strategies [9d,14c,18] . The 3,4‐substituted derivatives were obtained by alkylation of 3,4‐dihydroxybenzonitrile and subsequent 1,3‐dipolar cycloaddition of azide to yield tetrazoles 7 (R 3 =H, R 1 =R 2 =O‐alkyl).…”

“…The 3,4,5‐substituted derivatives were synthesized via alkylation of gallic acid ester, saponification, chlorination and ammonolysis of the acid chlorides to amides followed by dehydration/azide addition with a reagent formed in‐situ from silicon tetrachloride and sodium azide. [SI] Some of the so formed tetrazoles have recently been reported [9d,14] . Table 1 collects the BTT stars prepared by this procedure.…”

“…Furthermore, liquid crystalline oxadiazoles often show medium to high fluorescence quantum yields and are therefore also of interest for (non‐linear) optical applications [13] . In continuation of a project on star‐shaped materials, [9d,14] we report here luminescent discotic π‐systems composed of a central BTT disc with alkoxyaryl‐1,3,4‐oxadiazole arms. All, except 8 , are discotic liquid crystals with broad mesophases.…”

Mesogens with aggregation‐induced emission properties: Materials with a bright future

“…Detert and coworkers reported a series tetrakis(oxadiazolyl-phenyl)pyrazine-based emissive mesogens, which showed temperature ranges of columnar mesophases of up to 250 • C depending on the substitution [31,32] pattern (Figure 18). [45,46] Interestingly, the emissive behavior of the tetraphenylpyrazine derivatives (OXA-3) remained nearly unaffected by the substitution pattern as proven UVvis and fluorescence spectroscopy in solution using different solvents (λ em 440-455 nm). This observation also applied for OXA-3 derivatives (R 1 = H, R 2 = R 3 = C 14 H 29 or R 1 = C 12 H 25 , R 2 = H, R 3 = C 12 H 25 ) spin-coated thin films in the liquid crystalline phase.…”

2,5-Bis[(E)-2-phenylethenyl]-3,6-bis(pyridin-2-yl)pyrazine

“…The title compound 2,5-(E,E)-distyryl-3,6-di-(2-pyridyl)pyrazine, C 30 H 22 N 4 , was prepared as a reference chromophore in a project on pyrazine-centered materials, solvatochromic dyes (Schmitt et al, 2008, Wink & Detert, 2013 and liquid crystals (Rö der et al, 2019;Schmitt et al, 2011).…”