In daily life, we usually make materials with certain colors via dyes or pigments. However, there is a methodology for making specific nanostructures that reflect light under certain wavelengths, and ...this is considered structural color. In this study, we demonstrate novel sliced polymeric films exhibiting reflected purple, blue, cyan, and red colors via Bragg reflection. The pitch of the cholesteric liquid crystal was changed by altering the ratio of chiral dopant inside the liquid crystal mixture. It was confirmed that the reflected colors remained stable and did not change as the size and thickness of the sliced films were decreased. Furthermore, colorful patterns were easily achieved by using CLC slices as colorants, and these were fixed with transparent glue for image production. Theoretically, nanosized structural colorants could be prepared via a femtosecond laser. It is anticipated that these sliced polymerized cholesteric liquid crystal films can be applied in the surface coating and painting industries.
Uniformly sized cholesteric liquid crystal (CLC) shells are fabricated from a reactive CLC mesogen mixture via a microfluidic method with a fine-tuned density of the inner phase of the CLC shell by ...controlling the mixing ratio of glycerol and water. The solid-state CLC (CLCsolid) shell is obtained after UV curing and chiral-dopant extraction. Stable CLCsolid shells are obtained when the density of the inner phase is comparable to that of the CLC shell during UV curing. The CLCsolid shells display three modes of reflection patterns: central reflection (R cent), cross-communications among adjacent CLC shells (R comm), and reflection within the shell interior (R in). The three different modes of reflection of the CLCsolid shells are utilized for solvent sensors, anti-counterfeiting patches, and labeled templates for monodispersed droplets using their characteristics of differing swellings of CLCsolid shells in different organic solvents, the complexity of the R cent, R comm, and R in patterns, and the pores formed in the CLCsolid after chiral-dopant extraction, respectively. Thus, CLCsolid shells have intriguing photonic properties and can be applied in many different fields, which have previously not been explored with liquid crystal-state CLC shells.
•To save energy, a bistable dual frequency cholesteric liquid crystal display (BDFCLC) with a novel acrylic chiral dopant was fabricated.•The synthesized acrylic chiral dopant enhances the chiral ...efficiency by fixing the chiral dopant homogeneously.•The fabricated BDFCLC cell shows a high transmittance of 97.6% and a fast response time of 1.5 ms.•Each of the transparent “ON” and opaque “OFF” states was maintained without the bias of a continuous electric field.
Liquid crystal devices are popularly used in the design of smart windows. However, the continuous electric field required for their operation may cause unnecessary energy loss and there is a risk of state transition when the electric field disappears. To overcome these problems, bistable devices were developed that exhibit electro-optic memory. In this study, we demonstrate the synthesis of a novel liquid crystalline acrylic chiral dopant. The polymerizable chiral dopant is expected to disperse and be fixed in liquid crystals, homogeneously revealing higher chiral efficiency. Incorporation of the synthesized chiral dopant into the dual frequency cholesteric liquid crystal results in a bistable display performance with a high transmittance of 97.6% and a fast response time of 1.5 ms. Each of the transparent “ON” and opaque “OFF” states was maintained without the bias of a continuous electric field. The achieved results show the possible application of the synthesized acrylic chiral dopant on a bistable dual frequency cholesteric liquid crystal display (BDFCLC) for smart windows and other devices.
The continuous electric field required for their operation may cause unnecessary energy loss and there is a risk of state transition when the electric field disappears.
To fabricate a smart optical device with fast transition between “ON” and “OFF” states, and with continuously electric field addition, a new acrylic chiral dopant was synthesized and mixed with commercially available dual frequency nematic liquid crystal as a new cholesteric liquid crystal material possessing both perpendicular and planer arrangements with and without one-time electric field addition.
In this study, we demonstrate the synthesis of a novel liquid crystalline acrylic chiral dopant. The polymerizable chiral dopant is expected to disperse and be fixed in liquid crystals, homogeneously revealing higher chiral efficiency. Incorporation of the synthesized chiral dopant into the dual frequency cholesteric liquid crystal results in a bistable display performance with a high transmittance of 97.6% and a fast response time of 1.5 ms. Each of the transparent “ON” and opaque “OFF” states was maintained without the bias of a continuous electric field.
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•Designing of advanced FLCs through the fluorination of chiral dopants.•Fluorination of the chiral dopants tune the permittivity of the FLC mixture.•The fluorination of the chiral dopants influences ...the molecular alignment.•Reduction of spontaneous polarization by the screening of molecular chirality.
In this article, fluorinated chiral dopant-assisted tuning of dielectric and electro-optical properties of a ferroelectric liquid crystal (FLC) material is presented. Five new FLC mixtures with room temperature ferroelectric phase were formulated by fluorinating the phenyl core of chiral dopant at different positions and with a different number of fluorine atoms. The dielectric and electro-optical properties of all the FLC mixtures were systematically studied. It is found that the permittivity value of ferroelectric mesogens can be tuned between 5 and 36 (at 100 Hz) with fluorination. Also, the dielectric loss factor decreases owing to fluorination of chiral dopant with a shift in phason mode relaxation towards the low-frequency side. In addition, there is a significant change in material parameters of FLC, such as phase transition temperature, response time, spontaneous polarization, and rotational viscosity due to fluorination in chiral dopant. The presence of highly electronegative fluorine acts as a source of potentially repulsive force. It partially screens the molecular chirality of the dopant, which resulted in a change in the material parameters of FLCs. Interestingly, there is no considerable change in the mesogenic structure and orientation with the addition of fluorine, which is confirmed through wide-angle X-ray scattering. These studies open up a new avenue for tailoring the dielectric and electro-optical properties of mesogens for advanced device applications based on FLCs.
Herein, we suggest a unique approach to control the handedness of twisted lamellae in banded spherulites of a stereoregular polymer, isotactic poly(2‐vinylpyridine) (iP2VP). When (R)‐ or ...(S)‐hexahydromandelic acid (HMA), which can associate with iP2VP, was introduced as a chiral dopant, mirror‐image CD spectra in the complex systems showed induced circular dichroism (ICD) of the iP2VP by chiral HMA. Banded spherulites resulting from lamellar twisting due to the imbalanced stresses at the opposite folding surfaces could be formed by crystallization of the iP2VP/HMA complexes, which had a crystalline structure similar to that of neat iP2VP. A preferential sense of the twisted crystalline lamellae was found in the iP2VP/HMA complex, thus suggesting homochiral evolution from conformational to hierarchical chirality.
Not just a pretty pattern: The handedness of twisted lamellae in the banded spherulites of isotactic poly(2‐vinylpyridine) (iP2VP) was controlled by the crystallization of iP2VP with chiral dopants (see polarized‐light micrographs). Hexahydromandelic acid (HMA) induced circular dichroism in iP2VP. The mirror‐image CD spectra observed with (R)‐ and (S)‐HMA suggest homochiral evolution from conformational to hierarchical chirality in this system.
In this paper, a simple and powerful method to control the induced handedness of helical nanofilaments (HNFs) is presented. The nanofilaments are formed by achiral bent-core liquid crystal molecules ...employing a cholesteric liquid crystal field obtained by doping a rod-like nematogen with a chiral dopant. Homochiral helical nanofilaments are formed in the nanophase-separated helical nanofilament/cholesteric phase from a mixture with a cholesteric phase. This cholesteric phase forms at a temperature higher than the temperature at which the helical nanofilament in a bent-core molecule appears. Under such conditions, the cholesteric liquid crystal field acts as a driving force in the nucleation of HNFs, realizing a perfectly homochiral domain consisting of identical helical nanofilament handedness.
This Review focuses on recent advancements regarding the design of photoisomerizable chiral dopants which can switch the helical orientation in cholesteric liquid crystals upon light stimuli. Chiral ...dopants exhibiting conformational change in response to an external stimulus can provide dynamic control of the cholesteric pitch. Development of such responsive systems has been attempted since the 1970s. However, major advances on efficient chiral dopants exhibiting either high helical twisting power or large photoswitching have been achieved only in recent years. This Review covers photoresponsive low molecular weight cholesteric liquid crystal systems based on chiral dopants capable of photochemically “switching power to twist” surrounding liquid crystalline host molecules, “inverting” their handedness or even “inducing” helical organization from the racemic nematic phase.
Around the twist: Recent advances in the design of photoisomerizable chiral dopants which can switch the helical orientation in cholesteric liquid crystals upon application of a light stimulus are reviewed. Such systems may find application in advanced optical and mechanical functions.
Highly circularly polarized (CP) light is generated by using a twisted conjugated polymer structure with a small amount of chiral molecules as the light emitting layer of the OLED. It is confirmed ...that the luminous efficiency is increased by 60% compared to the conventional OLED structure.
Significant attention has been paid to improve the helical twisting power (β) and Δβ between the two different isomers of axially chiral azobenzene dopants in cholesteric liquid crystals (CLCs); ...however, the correlations between the vales (β and Δβ) with the molecular structures as well as photoisomerisation kinetics are far from clear. In this study, a series of binaphthyl-azobenzene cyclic dopants R1-R3 with different lengths of alkoxy chain was synthesised, which exhibited photochemically reversible trans-cis isomerisation in both organic solvents and liquid crystal hosts. When doping into a nematic liquid crystal, dopant R2 with one linking alkoxy group showed the highest values of β and Δβ. The results revealed that the β value was related to the dihedral angle between two naphthyl planes and the miscibility between the dopants and the host molecule. Moreover, Δβ was also depended on the photoisomerisation quantum yields. With increasing length of alkoxyl chain, the photoisomerisation rate constant of dopants increased upon ultraviolet irradiation and decreased for the reverse process upon visible light irradiation either in isotropic acetonitrile or in CLCs. These results enable the precise tuning of the pitch and selective reflection wavelength of CLCs.
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