Contactless dual-function sensors based on Si-cholesteric liquid crystal systems for optical identification

ConspectusMultifunctional integrated molecules are increasingly pivotal in various cutting-edge fields including materials science, nanotechnology, and biomedicine. Among these molecules, chiral fluorescent photoswitches (CFPSs) are a class of functional organic molecules that seamlessly integrate chiral, fluorescent, and photoresponsive characteristics. These properties, when combined, allow for a fascinating array of variations in chirality and fluorescence due to the structural changes induced by photoisomerization. The types of photoisomerization further influence these changes, resulting in a wide range of outcomes. In this Account, we present the progressive results of our ongoing research in the field of CFPSs, with a special emphasis on the dynamic regulation and photonics properties of chiral liquid crystal (LC) systems constructed with these molecular switches. To date, we have developed five different types of CFPSs based on α-cyanostilbenes, dicyanodistyrylbenzene, diaryldicyanoethene, sulfonated DAE, and azobenzene, respectively. We have actively explored the molecular engineering of these CFPSs, the performances of the chiral LC assemblies, and the constructed photonic devices that broaden their potential applications.The main focuses of this Account are structured around the concept of the "molecule engineering-properties-device applications" of the CFPSs. Crucially, CFPSs have the unique ability to amalgamate chiral and fluorescent properties within this photomodulation, serving as an effective medium to achieve sophisticated photomodulation effects. Given this, we focus on the molecular engineering of these CFPSs based on cyano positions, aryl modifications, linking sites, and binaphthyl handedness, which strongly affect the fluorescence intensity, emission wavelength, chiral-induction ability, photoisomerization conversion rate, and reversibility. The comprehensive analysis holds significant implications for guiding the future design and optimization of CFPSs. Furthermore, LC is a versatile enabling material that can integrate CFPSs to create self-assembled 1D helical superstructures known as cholesteric LC (CLC) or 3D blue-phase (BP) cubic structure systems. We reveal that these LC systems not only enable cross-scale regulation of CFPSs but also serve as highly efficient photonic devices in their own right. Such advanced photonic devices we constructed have the ability to adjust both the reflected color, the fluorescence properties, and circularly polarized luminescence (CPL), demonstrating significant potential for visual and smart applications.These systematic investigations emphasize the importance of the photoswitches' integrated chirality and fluorescence for optimized molecular design and fabrication, intrinsic regulation mechanism, and advanced photonic applications. Further systematic investigations, including molecular simulation, performance stability, and device friendship, will contribute to the rapid development of CFPSs-LC photonic devices that are suitable for practical applications.

Enhanced electrochemical and electro-optical properties of nematic liquid crystal doped with Ni:ZnCdS/ZnS core/shell quantum dots

In this work, some of the most important characteristics of chiral compounds as components of the liquid crystal (LC) systems are discussed. These characteristics are the helical twisting power of chiral dopants (CDs) in the induced cholesteric (N*) mesophases, the temperature dependence of the induced helical pitch (P) quantified by the dP/dT parameter and the influence of the CDs on the N* mesophase thermal stability characterized by the dTiso /dC parameter. The molecular structure influence on them for several systematic series of the N-arylidene derivatives of (S)-1-phenyl- and (S)-1-benzylethylamines as well as the chiral diastereomeric 2-arylidene-p-menthane-3-ones is considered.

Introduction. Liquid crystals (LC) are anisotropic optical media which have found broad application, in particular in LC displays and other photonic devices in the visible range. Little attention has been focused on studying LCs for conversion of radiation in the IR region of the spectrum, even though CO2 and other IR lasers are used in industry and medicine. Well-oriented nematic LC samples are strongly birefringent media, and are characterized by ordinary and extraordinary refractive indices no and ne. An electric field can change the orientation of LC molecules (the Frederiks effect), leading to a change in the effective refractive index along the direction of propagation of the light. In this case, the long axes of molecules of an LC with positive dielectric anisotropy are aligned parallel to the field direction, while in an LC with negative dielectric anisotropy they are aligned perpendicular to the field. This is a fundamental property of liquid crystals, and the basis for the operating principle of most photonic devices. Earlier in [1] a method was proposed for controllable filtration of IR radiation, based on a combination of the Frederiks effect and the Christiansen effect. The latter effect arises if particles are dispersed in a sufficiently transparent medium and the particle sizes are comparable with the wavelength of the incident light. In this case, the system transmits light in a narrow range of wavelengths, where the refractive indices are close for the particle material and the medium in which the particles are dispersed. Using LCs made it possible to control the position of the transmission maximum of the system when an electric field is applied. Application of this effect is also possible for a fixed value of the applied voltage (by varying its frequency). In this case, we propose using a dual-frequency LC as the medium in which the particles are dispersed, where the LC has positive anisotropy of the dielectric constant at low frequencies of the applied electric field and negative dielectric anisotropy at high frequencies. Aluminum oxide is used as the particle material; the refractive index of aluminum oxide varies considerably in the IR region of the spectrum [2]. In this paper, we present the results of a study of the Christiansen effect in an aluminum oxide particles — dual-frequency LC system.

A finger vein authentication system is proposed in this research. Biometrics is the science of determining a person's identity based on physiological or behavioral characteristics. Physical characteristics like fingerprints, a face or a retina, as well as personal characteristics like a signature, are included in these characteristics. Biometric features are significantly more difficult for attackers to replicate or fabricate than traditional methods, and they are extremely rare to lose. Biometric traits are used in the identification system, which increases security and dependability. The technology to verify vein patterns is still relatively new, compared with other human characteristics. The proposed work focuses on developing a contactless sensor to retrieve features from the hand's finger vein pattern using a Deep attribute Representation based Fractional Firefly method (DAR-FFF). Vein pattern identification scans the blood for hemoglobin using an infrared light source. After the participant's palm is placed over the sensing device, an infrared region beam from the device measures the orientation of the arteries. These ultraviolet wavelengths are absorbed by liquid hemoglobin in the vasculature, resulting in dark streaks on the map. The hand's finger has more intricate circulatory pathways and a variety of distinguishing characteristics. Image enhancement, skeletonization, and vein pattern chain code comparison are all processes in this procedure.

<p dir="ltr">It has been shown that liquid crystals can be used as the basis for new types of biosensors that detect bacteria, viruses, and gases. The application of liquid crystal biosensors is relatively new in the biotechnology, medicine, and food industries. Over the past few decades, this advanced material has shown its potential in a variety of applications, including electro-optical devices. Liquid crystals are viscoelastic and anisotropic materials that respond to analytes and change their optical properties accordingly. As a result, changes in optical properties can be visualized and used to detect analytes. When the liquid crystal is in contact with an aqueous interface, the chemical or biological agent is adsorbed by the liquid crystal and results in a change in the liquid crystal orientation in film or within droplets. The result of changing the bulk orientation of liquid crystal creates a texture that can be visualized by optical methods, such as a polarizing optical microscope. Understanding liquid crystal biosensors requires an understanding of bulk orientation and interface interaction in various geometries. In addition to investigating the created texture or optical pattern when polarized light is transmitted through the liquid crystal system. This research will utilize a mathematical model and computational approach to gain an understanding of the liquid crystal biosensor's performance. In this study, biosensors with the aqueous interface will be examined. The unsteady two-dimensional mathematical model is composed of the Leslie Ericksen theory incorporating the Frank free energy during the usage of liquid crystal biosensors. The model is solved numerically using the Galerkin finite element method. We examined the transient optical pattern and response time with various initial bulk and boundary conditions. In nematic liquid crystal biosensors, surface viscosity and homeotropic anchoring strength are investigated and their impact is characterized. This series of studies has been presented for the first time for the use of liquid crystal biosensors with the aqueous interface.</p>

A novel system for inducing pretilt angles in liquid crystals (LC) was devised. For this purpose thin layers of a LC mixture containing diacrylate molecules were spun on glass plates covered with rubbed polyimide films. The layers were then photopolymerized to form a gel by UV radiation. In this way the orientation within the pregel layer was frozen. In a cell construction when another LC system was brought in between such gel layers, it was found that a pretilt angle within the LC system was induced. The induced pretilt angle was found to be easily controllable by varying the thickness of the gel layer and a wide range of pretilt angles could be induced.

The possibility of precisely regulating and targeting drug release with mesophase or Liquid crystal drug delivery systems has drawn much attention recently. This review offers a thorough investigation of liquid crystal drug delivery systems with an emphasis on their mesogenic architecture. It describes the various liquid crystal forms such as thermotropic and lyotropic liquid crystals and their applicability in advanced drug delivery. Liquid crystals are used as excellent carriers due to their distinctive characteristics, such as stimuli-responsive drug delivery and sustained release patterns. Comprehending the materials that form mesophase provides insight into their distinct physiochemical characteristics and their use in drug delivery. This review highlights the important role lyotropic and thermotropic liquid crystals play in drug delivery, underscoring their considerable potential. The transition of thermotropic liquid crystals from their conventional technological applications to drug delivery has been studied. Nonetheless, a few challenges still need to be addressed, including formulation strategy refinement, regulating release rates, maximising the loading of hydrophilic drugs, and storage stability. In the pharmaceutical field, addressing these issues will open the door to a revolutionary paradigm that will revolutionise therapeutic outcomes and improve patient care.Graphical

: The research objectives of this grant are to (1) characterize phase transitions theoretically and experimentally in molecular crystal systems, (2) use the above understanding gained by light scattering studies and theoretical interpretation to apply to the more complex system of lyotropic liquid crystals, and (3) knowledge gained on the model systems of increasing complexity is then applied to polymer liquid crystals and solid polymers as observed by laser light scattering techniques. Objective one has been definitely achieved as can be seen from the number of papers written in the last few years. Systems to have been experimentally and theoretically discussed are: trioxane, triazine, benzil, and chloranil. Others still to be investigated are: biphenyl, urea, thiourea, and hexamethyl benzene. Studies of lyotropic liquid crystals (sodium decyl sulfate, sodium sulfate, decanol, water) have been progressed to the point at which we will be reporting this data shortly. The major findings are: a number of phase transitions occur between 20 and 60 C; these transitions evidence strong critical behavior and long correlation times for fluctuations; and liquid crystals can be studied by light scattering in a unique and meaningful manner. Finally, some polymer studies were started which will be continued into the coming contract period. Spectra of solid powders, ribbons, and liquid crystals of PBT and solid PBO were obtained.

Formulation and evaluation of itraconazole via liquid crystal for topical delivery system.

The lacking of automatic screen systems that can deal with large volume of time-lapse optical microscopy imaging is a bottleneck of modern bio-imaging research. In this paper, we propose an effective automated analytic system that can be used to acquire, track and analyze cell-cycle behaviors of a large population of cells. We use traditional watershed algorithm for cell nuclei segmentation and then a novel hybrid merging method is proposed for fragments merging. After a distance and size based tracking procedure, the performance of fragments merging is improved again by the sequence context information. At last, the cell nuclei can be classified into different phases accurately in a continuous hidden Markov model (HMM). Experimental results show the proposed system is very effective for cell sequence segmentation, tracking and cell phase identification.

A mechanical molecular rotation model for liquid crystal (LC) systems is employed to evaluate phase transition temperature of fluorinated phenylbicyclohexane isomeric LC compounds. Results show that when a fluorine atom is substituted along the molecular long axis, an LC molecule acquires high rotational speed and its rotation becomes stable, thereby resulting in a better thermal stability of the nematic phase. A novel explanation is proposed for the behavior of the nematic-isotropic phase of the LC system when a heavy atom is substituted along the molecular long axis.

We point out that the global symmetries of the Yang-Mills theory in the Landau gauge support existence of variables similar to director fields in liquid crystal systems. We discuss two different types of the liquid crystal variables associated with the group of global Euclidean rotations and with a residual global group of color transformations. These global symmetries allow to identify various topological defects which resemble, in particular, vortex-like disclination defects and monopole-like objects in nematic liquid crystals. We suggest that the deconfinement phase transition in the Yang-Mills theory may be associated with a phase transition in a liquid crystal.

Improvement of rewriting time of optically driven liquid crystal display by azo-dye doping

Recent optical kerr effect (OKE) studies have revealed that orientational relaxation of rodlike nematogens near the isotropic-nematic (I-N) phase boundary and also in the nematic phase exhibit temporal power law decay at intermediate times. Such behaviour has drawn an intriguing analogy with supercooled liquids. Here, we have investigated the single-particle and collective orientational dynamics of a family of model system of thermotropic liquid crystals using extensive computer simulations. Several remarkable features of glassy dynamics are on display including non-exponential relaxation, dynamical heterogeneity, and non-Arrhenius temperature dependence of the orientational relaxation time. Over a temperature range near the I-N phase boundary, the system behaves like a fragile glass-forming liquid. Using proper scaling, we construct the usual relaxation time versus inverse temperature plot and explicitly demonstrate that one can successfully define a density dependent fragility of liquid crystals. The fragility of liquid crystals shows a temperature and density dependence which is remarkably similar to the fragility of glass forming supercooled liquids. Energy landscape analysis of inherent structures shows that the breakdown of the Arrhenius temperature dependence of relaxation rate occurs at a temperature that marks the onset of the growth of the depth of the potential energy minima explored by the system.