Liquid Crystal Dye Research Articles

84‐2: Flexible Dye Liquid Crystal Dimming Film for Smart Window

Windows are important elements in the passenger cars that have a large impact on the light shading and heat insulation, affecting heating and lighting and interior space requirements in the cars. Flexible smart window plays an important role in human comfort and experience. In this review, we will discuss the next generation smart windows based on flexible dimming film and dye liquid crystal technology which can realized a step‐less dimming result through voltage switching, in such a way that comfortable lighting and temperatures in the car can be maintained.

P‐3.2: Research on the Structure and Optical Performance of Reflective Liquid Crystal Display

P‐3.2: Research on the Structure and Optical Performance of Reflective Liquid Crystal Display

Optical characterisation of dyed liquid crystal cells

ABSTRACT The guest-host liquid crystal display, first proposed in 1968, relies on controlling the orientation of dichroic dyes dissolved in a nematic liquid crystal host. Controlling the orientation of the liquid crystal and of the dissolved dye with an electric field allows control of the transmittance of the cell. Knowing the dielectric properties at optical frequencies of the dye and liquid crystal mixtures is crucial for the optimal design of guest-host liquid crystal devices. In this work, the dielectric functions of various layers in liquid crystal cells are described by models obeying the Kramers-Kronig relations: the Sellmeier equation for transparent layers and the causal Gaussian oscillator model for absorbing layers. We propose a systematic way to accurately model the dielectric response of each layer by minimising the sum of squared differences between the measured transmittance spectrum of a guest-host cell in the near-UV/vis range and the prediction of the transmittance of the modelled multilayer structure. By measuring the transmittance for incident light polarised parallel and perpendicular to the nematic director allows us to separately characterise the two principal dielectric functions of the uniaxial sample. Our results show that the causal Gaussian oscillator model can accurately characterise the dielectric functions of dyes in liquid crystals.

Programming and Dynamic Control of the Circular Polarization of Luminescence from an Achiral Fluorescent Dye in a Liquid Crystal Host by Molecular Motors

AbstractCircular polarized light is utilized in communication and display technologies and a major challenge is to develop systems that can be switched between left and right circular polarized luminescence with high degrees of polarization and enable multiple addressable stable states. Luminescent dyes in Liquid Crystal (LC) cholesteric phases are attractive systems to generate, amplify and modulate circularly polarized luminescence (CPL). In the present study, we employ light‐driven molecular motors as photo‐controlled chiral dopants in LCs to switch the handedness of the LC and the circular polarization of luminescence from an achiral dye embedded in the mesogenic material. Tuning of the color of the CPL and the retention time of the photoprogrammed helicity is demonstrated making use of a variety of motors and dyes. The flexibility offered by the design based on inherently chiral unidirectional rotary motors provides full control over CPL non‐invasively by light, opening possibilities for pixilated displays with externally addressable polarization.

Programming and Dynamic Control of the Circular Polarization of Luminescence from an Achiral Fluorescent Dye in a Liquid Crystal Host by Molecular Motors.

Circular polarized light is utilized in communication and display technologies and a major challenge is to develop systems that can be switched between left and right circular polarized luminescence with high degrees of polarization and enable multiple addressable stable states. Luminescent dyes in Liquid Crystal (LC) cholesteric phases are attractive systems to generate, amplify and modulate circularly polarized luminescence (CPL). In the present study, we employ light-driven molecular motors as photo-controlled chiral dopants in LCs to switch the handedness of the LC and the circular polarization of luminescence from an achiral dye embedded in the mesogenic material. Tuning of the color of the CPL and the retention time of the photoprogrammed helicity is demonstrated making use of a variety of motors and dyes. The flexibility offered by the design based on inherently chiral unidirectional rotary motors provides full control over CPL non-invasively by light, opening possibilities for pixilated displays with externally addressable polarization.

P‐111: Research on the Structure and Optical Performance of Reflective Liquid Crystal Display

In this article, we designed two different Reflective liquid‐crystal displays (RLCD) structures using PDLC with high haze and high transparency, and discussed the influence of dye of liquid crystal and reflective particles in different structures on the display effect. Dye liquid crystals have a bright future in reflective display, but the influence of dye concentration on color gamut still needs further verification. When the TiO2 reflective particles are added to the color film (CF) to increase the reflectivity, because the reflection occurs on the surface of the film, adding higher concentration of TiO2 in a thin film shows the best display effect.

Strong CPL-active liquid crystal materials induced by intermolecular hydrogen-bonding interaction and a chirality induction mechanism.

A novel co-assembly material can emit strong CPL signals (λem = 485 nm, glum = +0.076/-0.064) from an achiral AIE-active β-cyanostilbene (CYS) liquid crystal dye through intermolecular hydrogen bond (HB) interaction and chirality induction after a rapid cooling quench treatment.

26.4: Invited Paper: Preparation and Spectral quality of Naphthalene Derivatives Dichroic Liquid Crystal Dyes

A series of new dyes based on 4‐bromo‐1, 8‐naphthaliminde had been designed, synthesized and evaluated. Spectroscopic tests of those compounds exhibited that these dyes emitted yellow‐green fluorescence at 490‐520 nm and had high quantum yields 0.76. Those dyes suggested positive fluorescent dichroism, when dispersed in LC E7, SA and SF which were up to 0.51, 0.41, respectively. The dye and LC E7 were mixtured and then did the photoelectric test. Mass spectrometry, NMR and melting point were characterized. Ultraviolet and fluorescence spectra were tested in the isotropic solvents, and the absorption and emission spectra in the anisotropic liquid crystal.

Synthesis and Evaluation of Naphthalene Anhydride Fluorescence Dichroic Liquid Crystal Dye

Liquid crystals are materials which has properties between those of conventional liquid those of solid crystals There are many different types of liquid-crystal phases, which can be distinguished by their different optical properties. When viewed under a microscope using a polarized light source, different liquid crystal phases will appear to have distinct textures.The contrasting areas in the textures correspond to domains where the liquid-crystal molecules are oriented in different directions. Liquid crystal material is mainly used for liquid crystal displays, which rely on the optical properties of certain liquid crystalline substances in the presence or absence of anelectric field . In a typical device, a liquid crystal layer sits between two polarizers that are crossed oriented to one another. Color LCD systems use the same technique, with color filters used to generate red, green, and blue pixels. Due to the use of polarizer, the utilization rate of light is decreased obviously. Guest-host liquid crystal displays have many advantages, such as displaying information in excellent colour, good contrast ratio, a large viewing angle, high brightness and the need for only one or no external polarizers at all, so they can’t lead to excessive energy loss of beaming light and low brightness. A series of naphthalene anhydride fluorescence dichroic liquid crystal dye (Z) have been designed and synthesized. Some of them have wide liquid crystal phase and bright fluorescence. All the Z molecules are tested for spectral properties, including UV-Vis, fluorescence and polarization spectra. The liquid crystal molecules have been tested for threshold voltage. All the new molecules are tested nuclear magnetic resonance spectroscopy and mass spectrometry. The properties of all the synthesized molecules are studied and analyzed. The absorption wavelength of Z series of naphthalimide fluorescent liquid crystal dye are at around 390 nm and emission wavelength are at around 500 nm. Bright yellow-green fluorescence was observed and the maximum fluorescence quantum yield reaches up to 0.88. Stokes shift are more than 100 nm. The maximum absorption order parameter of Z, SA is 0.69 and SF is between 0.45-0.63 in liquid crystal E7. In the negative liquid crystal BHR28000-300, the order parameter of Z with the applied voltage of 10V is up to 0.84. DSC test showed that Z have wide phase transition temperature. Acknowledgements We are grateful to the National Natural Science Foundation of China (21576043), supported by “the Fundamental Research Funds for the Central Universities”.

Dye-liquid-crystal-based biosensing for quantitative protein assay

Dye liquid crystals (DLCs) have been extensively investigated in the field of liquid crystal display, but their potential in biosensing has not been explored. To provide insights into the potential of DLCs as a means of biosensing material, a DLC-based biosensor was developed for protein detection and quantitation. Unlike dye-doped LCs, the DLC used in this study contains an azobenzene LC molecule chemically modified with two azo groups as chromophores, enabling the DLC to exhibit unique optical anisotropy and dichroic absorption at 470 nm, which were exploited in the quantitation of bovine serum albumin (BSA). The change in orientation of DLC molecules from the homeotropic to a disrupted state by BSA immobilized on the aligning-layer surface was evaluated in terms of the relative loss in transmittance, expressed by the standard parameter S%, due to the absorption as well as scattering of light. The DLC-based protein assay was capable of determining the BSA concentration, with which S% varied linearly between 1 μg/ml and 7.5 μg/ml. When the DLC molecules were reoriented from a BSA-disrupted state to the homeotropic alignment by an externally applied electric field, a linear correlation between S% and BSA concentration could be also derived from the voltage–transmittance plots. The unique electro-optical properties of the intrinsically dichroic DLC are promising toward the development of a simple and reliable sensing platform for the quantitative analysis of biomolecules.

Interplay between Long-Range Crystal Order and Short-Range Molecular Interactions Tunes Carrier Mobility in Liquid Crystal Dyes

We investigated the influence of molecular packing on the optical and electrical properties of the liquid crystalline dye 4,7-bis[5-(2-fluoro-4-pentyl-phenyl)-2-thienyl]-2,1,3-benzothiadiazole (FPPTB). FPPTB is crystalline at room temperature, exhibits a nematic phase at temperatures above 149 °C and is in an isotropic melt at temperatures above 230 °C. Solution processed FPPTB films were subject to thermal annealing through these phase transition temperatures and characterized with X-ray diffraction and polarized optical microscopy. Cooling FPPTB films from the nematic and isotropic phases increased crystal domain size, but also induced local structural variations in the molecular packing of crystalline FPPTB. The decrease in long-range order was correlated with an increase in short-range π–π interactions, leading to changes in molecular aggregation which persisted even when the FPPTB films were cooled to room temperature. Annealing-induced changes in molecular aggregation were confirmed with optical spectroscopy. The carrier mobility in FPPTB films increased over 2 orders of magnitude from (2.2 ± 0.4) × 10–5 cm2 V–1 s–1 in as-spun films to μ = (5.0 ± 0.8) × 10–3 cm2 V–1 s–1 in films cooled from the isotropic melt. We discuss the relationship between thermal stability and high carrier mobility values in terms of the interplay between long-range molecular order and increased π–π interactions between molecular pairs in the FPPTB film.

Thermal behaviour of CODA azoic dye liquid crystal and nanostructuring by drop cast and spin coating techniques

This study comes to complete the initial investigation of the liquid crystalline properties of 4-[(4-chlorobenzyl)oxy]-3,4′-dichloroazobenzene (CODA). Here, the thermal analysis of CODA dye was performed in air flow and nitrogen flow atmospheres by means of simultaneous thermogravimetry TG, derivative thermogravimetry DTG, differential thermal analysis DTA and differential scanning calorimetry DSC; differences between the two steps of the thermal degradation of CODA related to the two experimental atmospheres were observed. Drops cast and spin coating techniques were used for nanostructuring CODA on platinum (Pt) substrates; the deposited materials were characterised by atomic force microscopy (AFM) and scanning electron microscopy (SEM). Exotic crystalline nanowires of CODA were obtained as function of used deposition technique, while the deposition time decisively influenced their features. The present results advocate for employing these materials as template matrices for producing high-aspect-ratio inorganic nanomaterials (i.e. Au) in the form of nanotubes, nanowires, nanorods or nanoparticles with enhanced functional properties.

Dyes in Liquid Crystals: Experimental and Computational Studies of a Guest-Host System Based on a Combined DFT and MD Approach.

Practical applications of guest–host liquid crystal systems are critically dependent on the alignment of the guest species within the liquid crystal host. UV/Vis absorption spectroscopy shows that the 1,5-dihydroxy-2,6-bis-(4-propylphenyl)-9,10-anthraquinone dye aligns within the E7 nematic host, giving an experimental dichroic ratio of 9.40 and dye order parameter of 0.74. This alignment was modelled by using a combination of density functional theory (DFT) and molecular dynamics (MD) computational approaches that do not require the input of experimental data. Time-dependent DFT calculations show that the electronic transition dipole moment is highly aligned with the long molecular axis of the dye. Fully atomistic MD simulations show that the long axis of the dye is less highly aligned within the E7 host, indicating that this contribution limits the overall dye alignment and, thereby, the potential practical applications of this particular system. Importantly, this study demonstrates an experimental and combined DFT and MD computational approach that may be applied generally to guest–host systems, providing a potential route to their rational design.

Multiple hybridized resonances of IR-806 chromonic molecules strongly coupled to Au nanorods.

Strong coupling of plasmons and molecules generates intriguingly hybridized resonance. The IR-806 molecule is a near-infrared cyanine liquid crystal dye with multiple molecular bands and its tunable absorption spectrum varies dramatically with concentration. In this article, we investigate multiple hybridized resonances of the Au nanorods (AuNRs) strongly coupled to IR-806 molecules. Five hybridized resonance peaks are observed in the extinction spectra of the AuNR@IR-806 hybrids. Two resonance peaks at approximately 840 and 912 nm in the hybrids are reported for the first time. The dependence of the multiple hybridized peaks on the bare plasmon resonance wavelength of AuNRs and the molecular concentration is also demonstrated. The observations presented herein provide a plasmon-molecule coupling route for tuning optical responses of liquid crystal molecules.

Highly Dichroic and Luminescent Triphenodioxazine Dyes

Abstract We report herein a triphenodioxazine dye, which is highly dichroic and luminescent in liquid crystal (LC). The dye shows remarkable polarization dependence resulting from its high orientational order up to 0.88: the dichroic ratios from its absorption and that from the emission reach 22.1 and 67.7, respectively. Such high order has never been reported for luminescent dyes in LC, thus showing appreciable potential advantage for some applications.

Synthesis and study of azo dye compounds: variation of mesogenic behaviour with length of alkyl chains

The mesogenic behaviours of two azo dye liquid crystals, 1 and 4, differ because of the different length of terminal alkyl chains; azo dye 1 shows a SmB phase, azo dye 4 shows nematic and SmA phases during thermal processing. The molecular stackings of these two azo dye liquid crystals are compared on the basis of crystallographic studies to explain such unexpected mesogenic behaviour.

Star-shaped heptamers of discotic dyes as new materials for photovoltaic devices

AbstractPotentially n-type and p-type semi-conducting discotic liquid crystal dyes are linked together to star-shaped heptamers, which might self-organize into super-columns of separated p-type and n-type columnar stacks. Their synthesis, mesomorphism, and electronic properties will be discussed along with their potential use in photovoltaic devices.

N,N-Disubstituted-4-aminophenylazostyrylformate derivatives: their synthesis, mesogenic behaviour and photostability

A series of new azo dye liquid crystals was prepared by the reaction of the N,N-disubstituted-4-aminophenylazobenzaldehydes with butyl cyanoacetate in the presence of piperidine in refluxing ethanol. The new azo dye liquid crystals possess a SmA phase, and representative samples were found to be reasonably photostable.

Fluorescent 3-oxy benzanthrone dyes in liquid crystalline media

The behaviour of novel 3-oxy benzanthrone derivatives of intense fluorescence emission in liquid crystalline media has been studied with regard to their potential for display application. The optical properties of the dyes were examined both in organic solvents, nematic liquid crystal (LC) and polymer film. The influence of the dyes upon the phase transition temperatures and the electro-optical properties of LC in dye/LC systems was investigated in surface-stabilised display cells. The dichroism D(λ) and the orientational order parameters SA and SF of the dyes in LC were determined from absorption and fluorescence anisotropy. The effect of a polymer component added to the dye/LC systems upon the transition temperatures of LC was established.

Study of photoisomerization of azo dyes in liquid crystals

The trans-cis isomerization of azo dyes in liquid crystalline hosts is studied. It is shown that the full set of parameters governing the isomerization process can be deduced from polarized pump–probe transmission measurements. The results indicate that the dye order parameter for the trans isomer is relatively high and is strongly related to the liquid-crystalline order. The cis isomer exhibits a much lower dye order parameter and is not strongly dependent on the liquid-crystalline phase. The barrier to the thermal cis-trans relaxation is found to be relatively unaffected by the liquid-crystalline phase, while changes are observed in the pre-exponential factor.