Columnar and Smectic Liquid Crystals Based on Crown Ethers

Abstract

Unsymmetrical benzo[15]crown-5 ethers 5 with one lateral ortho-terphenyl unit bearing alkoxy side chains of varying chain lengths (C5-C14) were prepared from 3,4-dialkoxyphenylbromides 2. Complexation with metal salts MX (M = Na, Cs) afforded the corresponding derivatives MX5. The uncomplexed crown ethers 5 h and 5 i, with dodecyloxy and tetradecyloxy side chains, respectively, exhibit liquid crystalline properties. In the series of complexed crown ethers, liquid crystal properties appeared as early as NaI5 f with C9H19 side chains. Whereas the uncomplexed 5 h,i form smectic mesophases, the complexed NaI5 g and NaI5 h exhibit textures typical of columnar mesophases. These results were supported by X-ray diffraction measurements (WAXS, SAXS), which revealed smectic (5 h,i), rectangular columnar (NaI5 g), and hexagonal columnar (NaI5 h) mesophases. As the liquid crystalline phase might retain packing features of the solid-state structure, single-crystal X-ray analyses were also performed for some of the uncomplexed and complexed crown ether derivatives. The complex NaI(3)5 a displays a sandwich-type structure, with the crown ether cores mutually antiperiplanar and maintaining an almost perfect crown conformation. In contrast, non-mesogenic uncomplexed crown ether 5 b displays a layer-type ordering in the solid phase.

Counterion Effects on the Columnar Mesophases of Triphenylene‐Substituted [18]Crown‐6 Ethers: Is Flatter Better?

“…First, a system of VOF 3 as oxidant and BF 3 ·OEt 2 as a Lewis acid was used, which has been successfully applied to the synthesis of triphenylene-substituted [15]crown-5 ethers. [8] However, in the case of 1 b,d, this procedure led to decomposition instead of cyclization, even within a reaction time of just 5 min. Replacement of BF 3 ·OEt 2 by BA C H T U N G T R E N N U N G (OMe) 3 gave the desired products 2 b and 2 d, respectively, but due to incomplete reaction, mixtures of educt and product (1 b/2 b and 1 d/2 d) were obtained, which could not be separated by either recrystallization or column chromatography.…”

“…[8][9][10][11] Recently, we reported on dibenzo [18]crown-6 derivatives 1 with two lateral ortho-terphenyl units and their complexes MX·1 (M = K + , NH 4 + ). [12] It turned out that the anion X has a much stronger effect on their properties than the alkyl chain length.…”

Diskotische Flüssigkristalle: Von der maßgeschneiderten Synthese zur Kunststoffelektronik

“…Die Benzokrone-Struktureinheit mit nur einer oTerphenyleinheit wurde weiter untersucht. [45] Dabei war von Interesse, ob Benzo [15]krone-5-Derivate 150 (Schema 61) auch in Abwesenheit von Metallsalzen columnare Mesophasen bilden.…”

“…[45] Dagegen haben die entsprechenden NaI-Komplexe entweder rechtwinklig columnare Phasen (Kettenlänge C 10 ) oder hexagonal columnare Phasen (> C 10 ). Übereinstimmend mit den Ergebnissen von Percec et al [239] stellten wir für die Benzo [15]Krone-5-Komplexe 150·NaI fest, dass die Na + -Komplexierung die Mesophasenstabilität verbessert.…”

Columnar liquid crystals derived from crown ethers with two lateral ester-substitutedortho-terphenyl units: unexpected destabilisation of the mesophase by potassium iodide

“…Cation complexation not only induced novel mesophases or stabilised existing mesophases as observed for azacrowns with lateral ester groups [12], for oligophenylene vinylene benzocrown ether conjugates [15], or for taper-shaped crown ethers with gallic esters forming supramolecular channels [16][17][18][19][20][21], but even tuned the helicity of fibres made from chiral crown ether-substituted phthalocyanines as was published by Nolte and co-workers [22,23]. NaI complexes of unsymmetrical benzo [15]crown-5 ethers with one peripheral propeller-shaped ortho-terphenyl unit and four alkoxy side chains yielded columnar mesophases with a higher stability as compared to the corresponding salt-free systems [24]. On the other hand, a mesophase destabilisation by cation complexation was reported by He et al for calamitic liquid crystals bearing terminal crown ethers [25].…”