Chiral Memory on Transition between the B2 and B4 Phases in an Achiral Banana-Shaped Molecular System

Niwano, Hiroko; Nakata, Michi; Thisayukta, Jirakorn; Link, Darren R.; Takezoe, Hideo; Watanabe, Junji

doi:10.1021/jp0311355

Cited by 86 publications

(94 citation statements)

References 19 publications

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“…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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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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“…One such set of phases exhibited by bent-core liquid crystals (BCLCs) are optically isotropic, including the recently discovered B4 and the dark conglomerate (DC) phases. The discovery of these phases and the subsequent understanding of their internal structures are two of the major developments in the field of BCLCs [4][5][6][7][8][9][10][11][12][13][14][15][16]. A characteristic common to the DC and the B4 phases is spontaneous breaking of chiral symmetry that occurs even though the constituent molecules are achiral.…”

Section: Introductionmentioning

confidence: 99%

Understanding the unusual reorganization of the nanostructure of a dark conglomerate phase

et al. 2015

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The dark conglomerate phase exhibited by a bent-core liquid crystal material shows remarkable properties including an electric-field tuneable chiral domain structure and a large (0.045) reduction of refractive index, while maintaining an optically dark texture when observed under crossed polarisers. A detailed investigation of the system is presented, leading to a model that is fully consistent with the experimental observations. It reports the observation of two distinct regimes in the DC phase: a higher temperature regime in which the periodicity measured by small angle X-ray scattering decreases slightly (0.5%) and a lower temperature regime where it increases considerably (16%). Also, the paper discusses the unusual electric field-induced transformations observed in both the regimes. These changes have threshold fields that are both temperature and frequency dependent, though the phenomena are observed irrespective of device thickness, geometry and the alignment layer. The electro-optic behaviour in the DC phase correspond to a number of structural changes leading to unusual changes in physical properties including small (1%) increase in periodicity and a doubling of the average dielectric permittivity. We propose a model of the DC phase where in the ground state the nanostructure of phase exhibits an anticlinic antiferroelectric organization. Under an electric field, it undergoes a molecular rearrangement without any gross structural changes leading to an anticlinic ferroelectric order while keeping the overall sponge-like structure of the DC phase intact.2

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“…Freeze-fracture transmission electron microscopy (FFTEM) studies of the B4 phase revealed an assembly of twisted layers stacked to form chiral nanobundles with around wB40 nm widths and hB100 nm half pitch 6 . This helical nanofilament (HNF) phase is particularly interesting owing to its unique hierarchical nanostructure 7,8 in which the individual filaments further selforganize into oriented arrays of filaments that are phase coherent with respect to their twist. The bulk HNF phase expels most guest molecules, such as rod-shaped liquid crystals [9][10][11][12][13][14][15] , and their unique structure makes it attractive for the design of bulk and surface structures with controlled porosity and roughness at the nanometre and micrometre scales.…”

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confidence: 99%

Helical nanofilaments of bent-core liquid crystals with a second twist

et al. 2014

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The B4 phase of bent-core liquid crystals has been shown to be an assembly of twisted layers stacked to form helical nanofilaments. Interestingly, some of them have structural colours that cannot be explained by the nanofilaments alone. Here cryogenic-transmission electron microscopy observations on 40-120 nm films of four bent-core liquid crystal materials show that the filaments are present even in contact with a carbon substrate with only minor deformation, thus representing bulk properties. We find that the subsequent arrays of nanofilaments are not parallel to each other, but rotate by an angle of 35-40°with respect to each other. This doubly twisted structure can explain the structural colour. Being principally different from the packing of molecules in the twist grain boundary and blue phases, the double-twist structure of helical nanofilaments expands the rich word of nanostructured organic materials.

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Chiral Memory on Transition between the B2 and B4 Phases in an Achiral Banana-Shaped Molecular System

Cited by 86 publications

References 19 publications

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

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

Understanding the unusual reorganization of the nanostructure of a dark conglomerate phase

Helical nanofilaments of bent-core liquid crystals with a second twist

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