New Chiral Dopant Possessing High Twisting Power (original) (raw)
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Development of novel chiral dopants to be used in ferroelectric liquid crystal system
The study of chiral dopant and its application in liquid crystal system is one of the largest area of research in fluids leading to technological application in the field of display devices. Chiral dopant when mixed with achiral host mixture forms ferroelectric liquid crystal to be used in surface stabilised liquid crystal devices. 4-(pentyl, heptyl, nonyl)-2, 3 difluoro terphenyl nitriles and (S)-(−)-1-cyno-2-methylbutyl-4-pentyldifluoroterphenyl-4′-carboxylate were synthesised and mixed with achiral host mixture HM1 with the percentage of 3 and 7. Ferroelectric properties of synthesised FLC 1 were studied.
Ferroelectric C* phase induced in a nematic liquid crystal matrix by a chiral non-mesogenic dopant
Applied Physics Letters, 2015
We report on a ferroelectric chiral smectic C (C*) phase obtained in a mixture of a nematic liquid crystal (NLC) and a chiral nonmesogenic dopant. The existence of C* phase was proven by calorimetric, dielectric and optical measurements, and also by X-rays analysis. The smectic C* which is obtained in such a way can flow, allowing to restore the ferroelectric liquid crystal layer structure in the electro-optical cells after action of the mechanical stress, as it happens with the cells filled with NLC. The proposed method of obtaining smectic C* material allows us to create innovative electro-optical cell combining the advantages of NLC (mechanical resilience) and smectic C* (high switching speed).
Spectroscopy Letters, 2008
Structural, electro-optical, and dielectric investigations of a ferroelectric liquid crystal (FLC) exhibiting the chiral smectic C phase (SmC Ã ) are reported. This study has been performed on the pure FLC showing the SmC Ã -SmA-N Ã phase sequence and having high spontaneous polarization and a large relaxation frequency. We have determined the Goldstone rotational viscosity and the twist elastic constant in the SmC Ã phase from the experimental data of helical pitch, tilt angle, polarization, dielectric strength, and relaxation frequency of the Goldstone-mode relaxation. An Arrhenius-type behavior of the Goldstone rotational viscosity was obtained, and the corresponding activation energies were evaluated.
Review Chiral Liquid Crystals: Structures, Phases, Effects
2014
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.
Chiral and achiral banana shaped liquid crystals, Synthesis and characterization
It is known since 1996 that achiral bent-core (banana-shape) molecules may form polar smectic layers with ferroelectric or antiferroelectric behavior. 1 Soon it became also clear that the layers with tilted director structure may become chiral that can self assemble to macroscopically chiral (layer chirality is the same in subsequent layers) or racemic (layer chirality alternates in subsequent layers) structures 2 resulting thus a wealth phenomena of chirality and polarity leading to a new subfield of liquid crystal research. In the past several years great number of banana-shape compounds have been synthesized and characterized 3,4 , and at least eight different phases (chronologically assigned as B 1 ,…, B 8 ) have been described. 5,6,7,8 Among them the electro-optical switching has been observed only in the smectic B 2 , B 5 and B 7 phases. The most widely studied B 2 phase is identified as tilted antiferroelectric polar smectic (SmCP A ) phase with either synclinic (SmC s P A ) or anticlinic (SmC a P A ) structures 9 . B 7 phase is very unique and interesting due to its beautiful and extraordinary textures 6 , and it may have a double tilted director structure with C 1 symmetry. The B 1 phase has been designated as a columnar phase with rectangular lattice. The B 3 and B 4 phases are considered to be crystalline phases. Recently a growing number of bent-core materials have been found to show nematic phases, too. 11 Among rod-like liquid crystals, it is well known that Schiff's base type compounds tend to form smectic phases. The first smectic mesophases of banana-shaped molecules with five aromatic rings were discovered having azomethyne as connecting groups. It is found that the banana mesophase are very sensitive to the substituents connected to different positions of the aromatic rings keeping constant the molecular architecture. The situation is more complicated if the linking groups are changed for esters or vinyl-carboxylate groups. More and more banana shaped compounds with ester connecting groups were published 12 . Systematic work was carried out on investigating the influence of the carboxyl fuction on the mesomorphic properties in five aromatic ring bananas building up symmetrical and asymmetrical structures 13 . Schiff's base type compounds containing seven aromatic rings with ester connecting groups have been studied too. These compounds exhibited B 1 or B 2 mesophase. 14 The non-substituted series has enantiortpic B 2 , since the substitutents on the inner rings have less advantegous properties, and the B 2 phases became monotropic. So far little work has been devoted to oligomers and polymers based on banana monomers 15
Chiral Liquid Crystals: Structures, Phases, Effects
Symmetry, 2014
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.
Light-controllable chiral dopant based on azo-fragment: synthesis and characterisation
Liquid Crystals, 2022
Light-controllable chiral dopant based on azo-fragment: synthesis and characterization We present the newly synthesized chiral dopant 2-[(2-isopropyl-5methylcyclohexyl)oxy]-2-oxoethyl 4-{(E)-[4-(decyloxy)phenyl]diazenyl}benzoate (ChD-3501), consisting of azo-and aliphatic fragments together with a chiral center based on l-menthol as a reversible light-controllable chiral dopant. To assess the effects of UV/VIS irradiation and temperature in the isotropic and liquid crystalline (LC) states, we studied the spectral kinetics of ethanol solution of ChD-3501, as well as induction of the cholesteric helix when it was dissolved in nematic LC (E7) as a chiral dopant. The concentration dependence of the helical pitch of the induced cholesterics was studied by means on Grandjean-Cano method, and the helical twisting power of ChD-3501 in the nematic host E7 was determined. The reversible trans-cis isomerization of chiral dopandt ChD-3501 in E7 under UV/VIS irradiation was studied, and it has been found that the storage of the cis-isomer at certain constant temperature also leads to the reversible isomerisation, which presents a certain interest for applications.