Helix inversion in the chiral nematic phase of a ferroelectric liquid crystal containing a single chiral centre

Loubser, Christa; Wessels, Philippus L.; Styring, Peter; Goodby, John W.

doi:10.1039/jm9940400071

Cited by 28 publications

(24 citation statements)

References 7 publications

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“…Upon cooling down to the N* phase from isotropic melt, (+)-S-1 exhibited a strong negative Cotton effect in the absorption region of p ‐terphenyl, implying the formation of a left‐handed helix 44. The intensity of the Cotton effect decreased with reducing temperature and finally inverses from negative to positive at the N* to TGBC* transition, implying that the handedness of (+)-S-1 inversed from left in the N* state to right in the TGBC* state through a non‐helical chiral LC phase 16–24. Although (+)-S-2 was similar to (+)-S-1 in structure, it displayed a positive Cotton effect in the N* phase, an implication of right‐handed helix formation.…”

Section: Resultsmentioning

confidence: 97%

“…Later, Goodby et al13–15 found that the rule was also applicable to other liquid crystalline mesophases, like helicoidal smectics. More recent investigations have shown that, for certain types of chiral LCs, the twist sense also depends on temperature, which induces the change in the population of conformational isomers 16–24. For example, a thermotropic LC compound, 4″‐propoxymethylene‐2′‐fluoro‐4‐[(2 S , 3 S )‐3‐propyloxiran‐2‐ylmethoxy]‐[1,1′:4′,1″]terphenyl, exhibits a temperature‐dependent helix inversion in both the cholesteric (N*) and chiral smectic phases 22.…”

Section: Introductionmentioning

confidence: 99%

“…Other interactions can also induce a helix inversion. For example, the interaction between the fluoro substituents in the aromatic core and the chiral center of ( S )‐4‐ n ‐octyloxy‐2,3‐difluorobiphenyl‐4′‐yl‐3‐fluoro‐4‐(2‐fluorooctanoyloxy)benzoate induces a twist inversion in the N* phase 23, 26…”

Section: Introductionmentioning

confidence: 99%

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Tuning mesomorphic properties and handedness of chiral calamitic liquid crystals by minimal modification of the effective core

et al. 2011

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Two pairs of calamitic liquid crystalline molecules, (+)-2-[4'-(S)-sec-butoxyphenyl]-5-(4'-hexoxyphenyl)toluene ((+)-S-1) and (+)-2-(4'-hexoxyphenyl)-5-[4'-(S)-sec-butoxyphenyl]toluene ((+)-S-2), (-)-2-[4'-(R)-sec-butoxyphenyl]-5-(4'-hexoxyphenyl)toluene ((-)-R-1) and (-)-2-(4'-hexoxyphenyl)-5-[4'-(R)-sec-butoxyphenyl]toluene ((-)-R-2), have been designed and synthesized. Each of the molecules consists of a p-terphenyl core substituted with a methyl group on the middle ring, a chiral sec-butoxy tail, and an achiral n-hexoxy tail. The geometrical difference between (+)-S-1 ((-)-R-1) and (+)-S-2 ((-)-R-2) lies only in the location of the methyl group on the effective mesogenic core. Yet, such a small change in the structure gives rise to remarkable differences in mesogenic properties and handedness. Both (+)-S-1 and (-)-R-1 have an enantiotropic cholesteric phase (N*) and a monotropic twist grain boundary C* phase (TGBC*), whereas (+)-S-2 and (-)-R-2 exhibit only a monotropic N* phase. Moreover, (+)-S-1 ((-)-R-1) and (+)-S-2 ((-)-R-2) have opposite handedness in the N* phase, and (+)-S-1 and (-)-R-1 even have a helical inversion from N* to TGBC* phase through a non-helical chiral mesophase.

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Section: Resultsmentioning

confidence: 97%

Section: Introductionmentioning

confidence: 99%

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Tuning mesomorphic properties and handedness of chiral calamitic liquid crystals by minimal modification of the effective core

et al. 2011

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“…Die Molekülstrukturen einiger nematischer LCs zur Erzeugung von CLCs sind in Schema dargestellt. Es ist auch bekannt, dass CLCs eine Helixinversion in Abhängigkeit von der Temperatur eingehen können, allerdings sind diese Systeme nicht Thema dieses Aufsatzes. Es ist zu beachten, dass die temperaturinduzierte Chiralitätsumkehr von CLCs zwar von grundlegender wissenschaftlicher Bedeutung ist, potenzielle Anwendungen aber durch die erforderlichen hohen Temperaturen eingeschränkt sind.…”

Section: Lichtgesteuerte Chiralitätsumkehr In Helikalen Clc‐überstruunclassified

Lichtgesteuerte dynamische Chiralitätsumkehr in funktionalen selbstorganisierten helikalen Überstrukturen

Bisoyi

2016

Angewandte Chemie

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Helikale Überstrukturen sind weit verbreitet in der Natur, in synthetischen Polymeren und in supramolekularen Anordnungen. Die Steuerung der Chiralität (der Händigkeit) dynamischer helikaler Überstrukturen molekularer und makromolekularer Systeme durch externe Stimuli ist eine anspruchsvolle Aufgabe, die jedoch große Beachtung findet aufgrund des attraktiven Anwendungspotenzials von Materialien mit morphologieabhängigen, einstellbaren Eigenschaften. Die lichtgesteuerte Chiralitätsumkehr in selbstorganisierten helikalen Überstrukturen (d. h. cholesterischen, chiral‐nematischen Flüssigkristallen) steht derzeit im Mittelpunkt des Interesses, da durch die Umkehr der Händigkeit die Drehrichtung von selektiv reflektiertem, zirkular polarisiertem Licht verändert wird, woraus sich ein breites Anwendungspotenzial ergibt. Hier erörtern wir die aktuellen Entwicklungen bei der Chiralitätsumkehr cholesterischer Flüssigkristalle, die durch photoisomerisierbare chirale molekulare Motoren oder Schalter ermöglicht wird. Es werden verschiedene Klassen chiraler photoresponsiver Dotanden (Gastmoleküle) behandelt, die eine reversible lichtgesteuerte Chiralitätsumkehr helikaler Überstrukturen auf der Basis nematischer Wirtkomponenten bewirken können. Wege zum rationalen Design chiraler molekularer Schalter, welche die Chiralitätsumkehr helikaler Überstrukturen auf der Basis cholesterischer Flüssigkristalle bewirken, werden aufgezeigt. Wir hoffen, mit diesem Aufsatz eine Orientierungshilfe für den gezielten Entwurf weicher Materialien mit Potenzial zur stimuligesteuerten Chiralitätsumkehr und multifunktionaler Wirt‐Gast‐Systeme geben zu können.

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“…An interesting phenomena which is not too often observed is the so called cholesteric twist inversion [32][33][34][35][36]. While this is easily explained for mixtures of different components through a different temperature dependence of the pitch [37,38], it is much more surprising in a single component system.…”

Section: Propertiesmentioning

confidence: 99%

Chiral Liquid Crystals: Structures, Phases, Effects

2014

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The introduction of chirality, i.e., the lack of mirror symmetry, has a profound effect on liquid crystals, not only on the molecular scale but also on the supermolecular scale and phase. I review these effects, which are related to the formation of supermolecular helicity, the occurrence of novel thermodynamic phases, as well as electro-optic effects which can only be observed in chiral liquid crystalline materials. In particular, I will discuss the formation of helical superstructures in cholesteric, Twist Grain Boundary and ferroelectric phases. As examples for the occurrence of novel phases the Blue Phases and Twist Grain Boundary phases are introduced. Chirality related effects are demonstrated through the occurrence of ferroelectricity in both thermotropic as well as lyotropic liquid crystals. Lack of mirror symmetry is also discussed briefly for some biopolymers such as cellulose and DNA, together with its influence on liquid crystalline behavior.

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Helix inversion in the chiral nematic phase of a ferroelectric liquid crystal containing a single chiral centre

Cited by 28 publications

References 7 publications

Tuning mesomorphic properties and handedness of chiral calamitic liquid crystals by minimal modification of the effective core

Tuning mesomorphic properties and handedness of chiral calamitic liquid crystals by minimal modification of the effective core

Lichtgesteuerte dynamische Chiralitätsumkehr in funktionalen selbstorganisierten helikalen Überstrukturen

Chiral Liquid Crystals: Structures, Phases, Effects

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