The Origin of the Helical Twist Inversion in Single Component Cholesteric Liquid Crystals

Dierking, Ingo; Gießelmann, Frank; Zugenmaier, P.; Mohr, Karl‐Heinz; Zaschke, H.; Kuczyński, W.

doi:10.1515/zna-1994-1116

Cited by 28 publications

(23 citation statements)

References 2 publications

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“…The H‐PAs that were synthesized at low (−12 °C) and high (28 °C) temperatures exhibited right‐ and left‐screwed helical senses, respectively, that opposed those of the N*‐LCs required by the polymerization mechanism 37,38. Therefore, the current N*‐LC can produce hierarchically controlled helical structures consisting of the primary to higher‐order structure of H‐PA under thermal stimulus 17–23,39. This is the first report of chiral reaction field with thermally invertible helical sense that has the chemical functions and stability needed to serve as the medium for polymer reactions.…”

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confidence: 88%

Chiral Reaction Field with Thermally Invertible Helical Sense that Controls the Helicities of Conjugated Polymers

et al. 2020

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A chiral reaction field with thermally invertible helical sense enables control of the helicity of the reaction product, which is a central challenge in asymmetric synthesis that has yet to be overcome. A novel chiral compound comprising two types of chiral moieties with opposite helicities and temperature dependences is synthesized; this compound is added as a chiral dopant to a mixture of nematic liquid crystals to prepare a chiral nematic liquid crystal (N*‐LC). The N*‐LC containing the chiral dopant exhibits thermally invertible helicity to yield left‐ and right‐handed helical senses at low and high temperatures, respectively. Interfacial polymerization of acetylene is achieved in the N*‐LC by modulating the temperature. Helical polyacetylenes (H‐PAs) that are synthesized at low (−12 °C) and high (28 °C) temperature show right‐ and left‐handedness, respectively, in terms of the fibrils, fibril bundles, and spiral morphology. In addition, the helical sense of H‐PA is opposite that of the N*‐LC because of the peculiar polymerization mechanism for acetylene in the N*‐LC. The current N*‐LC is the first chiral reaction field that has not only the thermally invertible helical sense but also the chemical functions and stability needed to serve as the medium for polymer reactions.

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confidence: 88%

Chiral Reaction Field with Thermally Invertible Helical Sense that Controls the Helicities of Conjugated Polymers

et al. 2020

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“…In the other, the competition between the different temperature dependencies and opposite chiralities of multiple chiral centers causes the helix inversion 205, 206. Experimental support for the first explanation comes from NLCs doped with chiral dopants,207, 208 whereas results verifying the second explanation use diastereomeric LC compounds 209, 210…”

Section: Going Beyond the Reflectance Limitmentioning

confidence: 99%

Cholesteric Liquid Crystals with a Broad Light Reflection Band

2012

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The cholesteric-liquid-crystalline structure, which concerns the organization of chromatin, collagen, chitin, or cellulose, is omnipresent in living matter. In technology, it is found in temperature and pressure sensors, supertwisted nematic liquid crystal displays, optical filters, reflective devices, or cosmetics. A cholesteric liquid crystal reflects light because of its helical structure. The reflection is selective - the bandwidth is limited to a few tens of nanometers and the reflectance is equal to at most 50% for unpolarized incident light, which is a consequence of the polarization-selectivity rule. These limits must be exceeded for innovative applications like polarizer-free reflective displays, broadband polarizers, optical data storage media, polarization-independent devices, stealth technologies, or smart switchable reflective windows to control solar light and heat. Novel cholesteric-liquid-crystalline architectures with the related fabrication procedures must therefore be developed. This article reviews solutions found in living matter and laboratories to broaden the bandwidth around a central reflection wavelength, do without the polarization-selectivity rule and go beyond the reflectance limit.

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“…Nevertheless, it becomes apparent that all of these molecules incorporate at least two chiral elements, often chiral centers. It has been shown that the cholesteric twist inversion of single component systems can be explained by a superposition of the influences of each chiral center [39,40]. At last, of special interest are the optical properties of cholesteric phases.…”

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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The Origin of the Helical Twist Inversion in Single Component Cholesteric Liquid Crystals

Cited by 28 publications

References 2 publications

Chiral Reaction Field with Thermally Invertible Helical Sense that Controls the Helicities of Conjugated Polymers

Chiral Reaction Field with Thermally Invertible Helical Sense that Controls the Helicities of Conjugated Polymers

Cholesteric Liquid Crystals with a Broad Light Reflection Band

Chiral Liquid Crystals: Structures, Phases, Effects

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