New variants of polymorphism in banana­shaped mesogens with cyano­substituted central core

Wirth, I.; Diele, Siegmar; Eremin, Alexey; Pelzl, G.; Grande, S.; Kovalenko, L. G.; Pancenko, Natella; Weißflog, W.

doi:10.1039/b100924i

Cited by 152 publications

(102 citation statements)

References 14 publications

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“…• [19] and this agrees with that found by NMR experiments for systems similar to CK64. Also note that for intermediate E, the macroscopic biaxiality in the homeotropic cell is observed to be zero and in the planar cell the birefringence is found to be 0.112 ( fig.…”

Section: -P2supporting

confidence: 82%

Field-induced transformations in the biaxial order of non-tilted phases in a bent-core smectic liquid crystal

Panarin

Nagaraj

Vij

et al. 2010

EPL

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-The structural and electro-optic investigations of an achiral bent-core molecule in SmAPA phase, in which the polar directors in the neighboring layers are arranged antiferroelectrically, show that it undergoes transformation from one biaxial to another biaxial structure via a quasi-stable uniaxial structure on the application of the electric field. The noncontinuous change in biaxiality is explained by an intermediate state in which the secondary directors in the neighboring layers are perpendicular to each other.

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Section: -P2supporting

confidence: 82%

Field-induced transformations in the biaxial order of non-tilted phases in a bent-core smectic liquid crystal

Panarin

Nagaraj

Vij

et al. 2010

EPL

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“…One of them is that under polarizing microscope, we see no chiral domains of opposite handedness in the ground state of the DC phase. As we discussed, the DC phase consists of SmCP structure with short range interlayer correlation length [10][11][12][13][14][15][16][17][18][19]. The absence of opposite handed domains in our sample indicates two possibilities for the ground state arrangement of the layers: The adjacent layers are either homochiral (SmC s P S or SmC a P A type), making the overall structure chiral, though the opposite handed domains are smaller than the wavelength of the visible light.…”

Section: Discussionmentioning

confidence: 99%

“…During this process a simultaneous reversal in the polarization and the tilt direction takes place giving rise to a switching from SmC s P A to SmC a P S and SmC a P A to SmC s P S . Bent-core mesogens are well known for the optically isotropic phases they exhibit, which include the B4 phase [7][8][9], the dark conglomerate (DC) [10][11][12][13][14][15][16][17][18][19] and the dark enantiomeric (DE) phases [20]. The DC phase, which is the topic of interest of this paper, is usually found to occur below the isotropic phase.…”

Section: Introductionmentioning

confidence: 99%

Unusual electric-field-induced transformations in the dark conglomerate phase of a bent-core liquid crystal

et al. 2014

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Unusual behaviour of the dark conglomerate (DC) phase seen in an oxadiazole-based achiral bent-core liquid crystal, which has not previously been reported for the DC phase of other liquid crystals, is described. Under polarizing optical microscopy, we see no domains of opposite handedness in the ground state of the DC phase. However, it shows unusual transformations when an electric field is applied to the system: On increasing the electric field, at first the domains of opposite handedness become visible and then they grow in size and slowly the sample transforms to a monochiral or single handed form which is followed by a nonchiral state at very high fields. The threshold electric fields required to achieve these changes are temperature dependent and the transformations are seen irrespective of the frequency of the applied electric field (100 Hz to 5 kHz), type of the waveform (sine, square and triangular) and the thickness (1.5 µm to 15 µm) or the geometry (planar and twisted) of the device used. Further, there is no field-induced high birefringence texture observed even though sufficiently large electric field (~22 V/µm) has been applied across the devices. The nature of the behaviour is investigated by various techniques such as optical microscopy, conoscopy, circular dichroic and Raman spectroscopies, electro-optics and dielectric spectroscopy. The possible physical phenomena behind these changes are discussed in detail.

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“…This empirical fact raises the question whether there is a fundamental connection between polarity and chirality in molecular fluids. Another empirical observation is that bent-core materials exhibiting SmCP phases generally do not exhibit nematic phases, although two exceptions have recently been reported [10,11]. One objective of this study is to establish the molecular shape requirements for the occurence of the nematic phase in bent-core materials.…”

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confidence: 99%

Phase behavior of bent-core molecules

et al. 2003

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Recently, a new class of smectic liquid crystal phases (SmCP phases) characterized by the spontaneous formation of macroscopic chiral domains from achiral bent-core molecules has been discovered. We have carried out Monte Carlo simulations of a minimal hard spherocylinder dimer model to investigate the role of excluded volume interations in determining the phase behavior of bent-core materials and to probe the molecular origins of polar and chiral symmetry breaking. We present the phase diagram as a function of pressure or density and dimer opening angle ψ. With decreasing ψ, a transition from a nonpolar to a polar smectic phase is observed near ψ = 167• , and the nematic phase becomes thermodynamically unstable for ψ < 135• . No chiral smectic or biaxial nematic phases were found. [5]. In all of these examples, chirality is an intrinsic property built into the chemical structure of the LC molecules. Recently, a new class of smectic LC phases (SmCP phases) characterized by the spontaneous formation of macroscopic chiral layers from achiral molecules has been discovered [6,7]. The molecules comprising these phases have 'bow' or 'banana' shaped cores. The resulting phases exhibit two spontaneous symmetry-breaking instabilities: polar molecular orientational ordering within the layer plane, and molecular tilt, which together produce chiral layers with a handedness that depends on the direction of the tilt relative to the polar axis. Very large second order nonlinear optical (NLO) coefficients have been measured in the ferroelectric state of such materials, bearing some promising applications in NLO devices [8,9].From a theoretical point of view, the relationship of phase behavior to the specific bent-core molecular shape is of fundamental interest. In this paper, we investigate a minimal excluded volume model of bent-core mesogens, focusing on the molecular origin of polar and/or chiral symmetry breaking. Of particular interest is the coupling between polar and chiral symmetry breaking. In all bentcore materials studied to date, polar symmetry breaking is accompanied by chiral symmetry breaking induced by molecular tilt. This empirical fact raises the question whether there is a fundamental connection between polarity and chirality in molecular fluids. Another empirical observation is that bent-core materials exhibiting SmCP phases generally do not exhibit nematic phases, although two exceptions have recently been reported [10,11]. One objective of this study is to establish the molecular shape requirements for the occurence of the nematic phase in bent-core materials. Finally, we explore the possibility of biaxial nematic ordering in bent-core materials, motivated by recent experimental indications [11,12].Hard core models are particularly appealing due to their simplicity and relative ease of computation, both in simulation and theory. In particular, hard spherocylinders have been widely studied as simple models for conventional LCs [13,14]. This model exhibits rich phase behavior including isotropic, nematic, s...

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New variants of polymorphism in bananashaped mesogens with cyanosubstituted central core

Cited by 152 publications

References 14 publications

Field-induced transformations in the biaxial order of non-tilted phases in a bent-core smectic liquid crystal

Field-induced transformations in the biaxial order of non-tilted phases in a bent-core smectic liquid crystal

Unusual electric-field-induced transformations in the dark conglomerate phase of a bent-core liquid crystal

Phase behavior of bent-core molecules

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New variants of polymorphism in banana­shaped mesogens with cyano­substituted central core

Cited by 152 publications

References 14 publications

Field-induced transformations in the biaxial order of non-tilted phases in a bent-core smectic liquid crystal

Field-induced transformations in the biaxial order of non-tilted phases in a bent-core smectic liquid crystal

Unusual electric-field-induced transformations in the dark conglomerate phase of a bent-core liquid crystal

Phase behavior of bent-core molecules

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New variants of polymorphism in bananashaped mesogens with cyanosubstituted central core