Physics of liquid crystals of bent-shaped molecules

Jákli, Antal; Lavrentovich, Oleg D.; Selinger, Jonathan V.

doi:10.1103/revmodphys.90.045004

Cited by 153 publications

(130 citation statements)

References 493 publications

(522 reference statements)

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“…Bent‐core liquid crystals (BCLCs) are unique materials, since they may exhibit polar order and spontaneous symmetry breaking in ordered liquid crystalline fluids consisting of achiral molecules . The bent molecular shape causes differences also in other physical properties of BCLCs, such as anomalous anisotropies of elastic constants or a giant flexoelectric effect . In addition, the introduction of a functional group that allows for the modulation of the properties of BCLCs by means of magnetic field or light is nowadays of eminent interest.…”

Section: Introductionmentioning

confidence: 99%

Light Tunable Gratings Based on Flexoelectric Effect in Photoresponsive Bent‐Core Nematics

Jing

Xiang

et al. 2019

Advanced Optical Materials

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A new photoresponsive bent‐core nematic (BCN) material, which exhibits flexoelectric domains (FDs) driven by electric field, is reported. Unexpectedly, it is found that the morphologies of FDs can be controlled by irradiation with light fields. This light tunability is ascribed to the photoisomerization effect of the azo moiety within the BCN molecules, where the ratio of trans and cis isomers changes according to the parameters of the light field, resulting in adjustable electric threshold and periodicity of FDs. Based on this principle, a prototype of controllable optical grating is assembeled, whose operation can be manipulated by the wavelength or intensity of light. Due to the easy, instant, and remote operation by light, this optical, contactless tunability has a great advantage over traditional electric control in tunable photonic devices.

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Section: Introductionmentioning

confidence: 99%

Light Tunable Gratings Based on Flexoelectric Effect in Photoresponsive Bent‐Core Nematics

Jing

Xiang

et al. 2019

Advanced Optical Materials

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“…If smectic layers are formed of molecules with a shape that hinders molecular rotation, the molecules may orient in a way that the layer becomes polar. An example is a system made of molecules with a bent core, which are not chiral, but some phases they form have polar properties [2]. First compounds with bent-shaped molecules that formed liquid crystalline phases were intentionally designed and synthesized two decades ago [3].…”

Section: Introductionmentioning

confidence: 99%

Chiroclinic effect and the phase diagram of achiral polar molecules in the antiferroelectric smectic B2 phase

Jukić

Čepič

2019

Phys. Rev. E

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The paper presents a detailed analysis of the effects of chiral doping on antiferroelectric B 2 subphases in bent core systems. The studied system exhibits the phase sequence SmA ↔ SmAP A ↔ SmC S P A . The chiral dopant induces the tilt in the SmAP A phase or the tilt modulation in the SmC S P A phase, which is known as the chiroclinic effect, but it also influences the stability ranges and the order of the transition between the phases. The order of the phase transition changes from a continuous for weak effects of chiral doping to discontinuous for strong effects. Competition of interactions results in changes of the phase sequences, which are resumed in the phase diagram. The method that leads to these findings, which could be used for the analysis of other similar systems, is briefly presented as well.

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“…Different LC mesophase are principally characterised by their degree of positional order; the nematic LC phase possesses long range orientational order, whereas smectic phases also exhibit positional order in one dimension. The discovery of nematic phases in which the average orientational order varies periodically – so called modulated nematics – has recently attracted significant interest . The twist‐bend nematic phase (N TB ) exhibits a heliconical precession of the nematic director through space with a periodic length scale of a few tens of nanometers .…”

Section: Transition Temperatures (T °C) and Associated Enthalpies Omentioning

confidence: 99%

Utilising Saturated Hydrocarbon Isosteres of para Benzene in the Design of Twist‐Bend Nematic Liquid Crystals

Al-Janabi

Mandle

2020

ChemPhysChem

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The nematic twist-bend (N TB ) liquid crystal phase possesses a local helical structure with a pitch length of a few nanometres and is the first example of spontaneous symmetry breaking in a fluid system. All known examples of the N TB phase occur in materials whose constituent mesogenic units are aromatic hydrocarbons. It is not clear if this is due to synthetic convenience or a bona fide structural requirement for a material to exhibit this phase of matter. In this work we demonstrate that materials consisting largely of saturated hydrocarbons can also give rise to this mesophase.Furthermore, we find that replacement of 1,4-disubstituted benzene with trans 1,4-cyclohexane or 1,4-cubane does not especially alter the transition temperatures of the resulting material nor does it appear to impact upon the heliconical tilt angle. Each of these three units is effectively rigid and linear; calculating the probability distribution of bend angles for each compound reveals that the isosteric groups has little impact on the overall molecular shape, demonstrating the shape-driven nature of the N TB phase. Conversely, we find that incorporation of 2,6-disubstituted cuneane -a saturated hydrocarbon which is rigid but not linear -supresses the formation of the N TB phase.Liquid crystals are a collection of states of matter (mesophases) which possess orientational and/or positional order not found in the liquid state. Different LC mesophase are principally characterised by their degree of positional order; the nematic LC phase possesses long range orientational order, whereas smectic phases also exhibit positional order in one dimension. The discovery of nematic phases in which the average orientational order varies periodically -so called modulated nematics -has recently attracted significant interest. [1][2][3][4][5][6] The twist-bend nematic phase (N TB ) exhibits a heliconical precession of the nematic director through space with a periodic length scale of a few tens of nanometers. [7][8][9] This phase is typically found in materials comprising two or more mesogenic units which are mutually appended by a central spacer of such a length as to impart a gross bent shape. The incidence of the N TB phase is intimately linked to molecular shape, specifically the bend angle between adjacent mesogenic units. [10][11][12][13][14] The mesogenic units themselves are almost exclusively constructed from multiple benzene rings, and to date (as far as the authors are aware) the spacer is always appended to an aromatic ring rather than a saturated hydrocarbon; [15][16][17][18][19][20][21][22][23] it is not clear if this is a consequence of synthetic convenience or a real structural requirement for materials to exhibit this phase of matter.

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Physics of liquid crystals of bent-shaped molecules

Cited by 153 publications

References 493 publications

Light Tunable Gratings Based on Flexoelectric Effect in Photoresponsive Bent‐Core Nematics

Light Tunable Gratings Based on Flexoelectric Effect in Photoresponsive Bent‐Core Nematics

Chiroclinic effect and the phase diagram of achiral polar molecules in the antiferroelectric smectic B2 phase

Utilising Saturated Hydrocarbon Isosteres of para Benzene in the Design of Twist‐Bend Nematic Liquid Crystals

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