Room-temperature Liquid Crystal Research Articles

Room-Temperature Liquid Crystalline Tetraphenylethylene-Surfactant Complex with Chiral Supramolecular Structure and Tunable Circularly Polarized Luminescence.

A novel room-temperature liquid crystal of tetraphenylethylene derivative (TPE-DHAB) was synthesized using an ionic self-assembly strategy. The TPE-DHAB complex exhibits typical aggregation-induced emission properties and a unique helical supramolecular structure. Moreover, the generation and handedness inversion of circularly polarized luminescence (CPL) can be achieved through further chiral solvation, providing a facile approach to fabricate room-temperature liquid crystalline materials with controllable supramolecular structures and tunable CPL properties through a synergistic strategy of ionic self-assembly and chiral solvation process.

Proposed prototype for a quantitative biosensor for insulin detection using a liquid crystal

In this paper, we present a novel approach for label-free detection of human insulin using 5CB liquid crystal (LC). Monitoring insulin levels in the body is essential for treating diseases like diabetes, which are caused by insufficient production or inefficient use of insulin. Contemporary techniques of detection rely on glucose detection, and limited information is available on the direct detection of insulin. A simple method using a common room temperature LC 4-cyano-4-pentyl biphenyl (5CB) interacting with different concentrations of insulin, observed through a polarising optical microscope (POM), is reported in this paper. An analysis of observed textures revealed the detection of insulin as low as 25 μM concentration. The distinguishable features of the observed textures provide a scale for estimating insulin concentration. The effect of different pH and salt concentrations was studied in order to understand the optimal working condition of the proposed biosensor. Image J analysis demonstrated a positive correlation (R2 equal to 0.9553) between grey index (GI) values and human insulin concentrations. RGB analysis and interference studies confirmed the biosensor’s specificity in insulin detection. To correlate the textures to the happenings at the molecular level, docking studies were carried out. In addition to this, properties such as aromaticity, H-bond, hydrophobicity, interpolated charges, ionizability and solvent accessible area (SAS) in the minimum energy binding sites of 5CB-LC and human insulin chains were measured to know more about the interaction properties. This novel strategy shows promise for improving insulin detection sensitivity and accuracy, ultimately leading to better diabetes management and healthcare outcomes.

Temperature-dependent hole mobility in pyrene-thiophene-based room-temperature discotic liquid crystals.

π-Conjugated pyrene-thiophene-based room-temperature discotic liquid crystals armed with four peripheral aliphatic chains are reported to study their potential use in a hole-transporting organic semiconductor. The charge carrier mobility studies using the ToF method revealed room temperature hole mobility in the order of 10-4 cm2 V-1 s-1 for both mesogens. However, the mobility values for compound 1a were observed in the order of 10-3 cm2 V-1 s-1 at high temperatures. Such molecular systems can potentially be used in nonlinear organic electronic applications.

Understanding the effects of targeted modifications on the 1 : 2 Choline And GEranate structure.

1 : 2 Choline-and-geranate (CAGE) is an ionic liquid (IL) widely studied for its biomedical applications. However, both its industrial-scale preparation and its long-term storage are problematic so finding more suitable candidates which retain its advantageous properties is crucial. As a first step towards this we have conducted a targeted modification study to understand the effects of specific functional groups on the properties of CAGE. 1 : 2 Choline-and-octanoate and 1 : 2 butyltrimethylammonium-and-octanoate were synthesised and their thermal and rheological properties examined in comparison to those of CAGE. Using differential scanning calorimetry and polarising microscopy, the model compound was found to be an isotropic liquid, while the analogues were room-temperature liquid-crystals which transition to isotropic liquids upon heating. Dynamic mechanical analysis showed that the thermal behaviour of the studied systems was even more complex, with the ILs also undergoing a thermally-activated relaxation process. Furthermore, we have used electron paramagnetic resonance (EPR) spectroscopy, along with a variety of spin probes with different functional groups, in order to understand the chemical environment experienced by solutes in each system. The EPR spectra indicate that the radicals experience two distinct environments (polar and nonpolar) in the liquid-crystalline phase, but only one average environment in the isotropic phase. The liquid-crystalline phase experiments also showed that the relative populations of the two domains depend on the nature of the solutes, with polar or strongly hydrogen-bonding solutes preferring the polar domain. For charged solutes, the EPR spectra showed line-broadening, suggesting that their ionic nature leads to complex, unresolved interactions.

Frequency response of dielectric relaxation modes in a room temperature antiferroelectric phase liquid crystalline mixture

Thermodynamic, optical, and electrical characterization of a newly formulated mixture of chiral mesogenic molecules has been carried out. The material exhibits different mesophases like paraelectric smectic (SmA*), ferroelectric chiral smectic (SmC*) with synclinic structure, and wide temperature range antiferroelectric chiral smectic (SmCa*) with anticlinic structure. These studies show that at room temperature, the SmCa* phase is present in a wide temperature range of ∼128 °C (from −35.0 °C to 92.6 °C) followed by the SmC* phase (from 92.6 °C to 110.8 °C) as well as SmA* phase (from 110.8 °C to 113.9 °C). Besides the wide temperature range, the SmCa* phase has also been optimized for high helical pitch length, which is useful for helix unwound cells through surface stabilization for application. Frequency-dependent dielectric parameters have been determined for the material in the frequency range of 1 Hz to 40 MHz. The dielectric spectroscopy shows six different relaxation modes in various phases due to the collective and individual molecular behavior. The SmA* phase exhibits soft mode relaxation associated with variations in the amplitude of the tilt angle. The identified soft mode is significantly temperature-dependent. Using the Curie-Weiss law, the transition temperature for the paraelectric SmA* phase to the ferroelectric SmC* phase (Tc) is found to be 111.4 °C. Two relaxation modes in the SmC* phase have been identified Goldstone mode and a domain mode. These modes have extremely high dielectric strength resulting in high permittivity in comparison with other modes. Three modes of relaxation have been detected in the antiferroelectric SmCa* phase. Different characteristic parameters of these modes are strongly temperature-dependent. This study signifies that the present room-temperature antiferroelectric liquid crystals may be a potential candidate for display applications.

Synthesis and properties of long-lived room-temperature phosphorescent liquid crystal polymers based on “Jacketing” effect

Polymerization is one of the most widely used strategies to achiever RTP. To date, various polymer-based RTP materials have been reported. However, how to improve the phosphorescence lifetime of polymer-based RTP materials still needs to be further researched. In this article, we proposed a new strategy to realize long-lived room-temperature phosphorescence by utilizing the “jacketing” effect of mesogen-jacketed liquid crystal polymers. Two polymers PMJ0DFM and PMJ6DFM with different flexible spacer length were synthesized, and their liquid crystal phase structures and photo-physical properties were systematically investigated. PMJ0DFM formed columnar nematic phase while PMJ6DFM formed a more ordered hexagonal columnar phase liquid crystal. For PMJ0DFM without spacer length, due to the strong “Jacketing” effect, the thermal motion of the chromophore was suppressed, and it was also more conducive to the aggregation and planarization of the chromophores. Therefore, PMJ0DFM film showed longer phosphorescence lifetime and more red-shifted phosphorescence spectrum than PMJ6DFM film. The phosphorescence lifetimes of PMJ0DFM and PMJ6DFM were 355 ms and 247 ms, respectively. In addition, we also explored their application in linearly polarized luminescent materials. When oriented, PMJ0DFM and PMJ6DFM film could emit efficient linearly polarized room temperature phosphorescence.

4D direct laser writing of photo-triggered liquid crystal elastomer microactuators with large actuation strain

4D printed photo-triggered liquid crystal elastomers (LCEs) microactuators by direct laser writing via two-photon polymerization (DLW-TPP) have attracted increasing attention due to their manipulation flexibility, reversible and rapid actuation capabilities. However, their development is hampered by the lack of room-temperature printable liquid crystal (LC) photoresists. Here, we developed new light-responsive LC photoresists by incorporating novel conjugated polymers (CPs) as photothermal agents for the DLW-TPP technology. The CPs displayed a remarkable photothermal effect and effectively avoided the aggregation problems that always happened for inorganic nanoparticles in photoresists. Moreover, the CPs incorporation lowered the nematic-to-isotropic temperature of the LC photoresists which is beneficial for room-temperature DLW-TPP. The printing parameters, including laser power and scanning speed, were investigated using the developed LC photoresists. It was found the range of printing parameters decreased with the increase of the CPs loading fraction from 0.1 to 0.5 wt%, which was attributed to the high photothermal conversion efficiency (52.7%). A well-defined CPs/LCEs microactuator with CPs as low as 0.3 wt% was printed, which could achieve a large 25.0% actuation strain in 5 s upon near-infrared (NIR) light stimulation. It could be used for thriving soft micro-robotics and micro-membranes with controllable separation capabilities.

Synthesis, characterization and photophysical study of cholesterol functionalized azo-based room temperature liquid crystals

Four new liquid crystalline materials (HA1-HA4) with cholesteryl group and azo-ester linking group interconnected with two-side substituted flexible alkoxy side chains were deliberated and synthesized. The structure confirmation of the azo mesogens was investigated by using FT-IR, 1H NMR, and 13C NMR techniques. The phase behavior of the materials was investigated by crossed polarizing optical microscopy (POM), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and X-ray diffraction (XRD) techniques. All four targeted materials shows smectic type mesogenic properties and further stabilized up to room temperature to lower temperature. The structure-property relationship of present azo-based materials was discussed to investigate the scope of mesogenic properties. All four materials (HA1-HA4) display wide temperature range mesophase as 52.5 °C, 54.7 °C, 52.7 °C, and 54.1 °C. The photoresponsive properties of the azo-based bi-substituted materials were well examined by UV study.

Room-temperature triphenylene-based discotic liquid crystal dimers: effects of amide linkage and central fluoromethylene spacer

ABSTRACT Two series of triphenylene-based dimers both having a central fluoromethylene spacer of four or six carbon atoms and ester or amide linkages were synthesised and their phase behaviour investigated. All the synthesised dimers are room-temperature discotic liquid crystals and exhibit hexagonal columnar mesophases that supercool into a stable anisotropic columnar glass. The length of the fluoromethylene spacer has a minor effect on the phase transition temperatures of these dimers. However, dimers 1a and 2a with a (CF2)4 spacer exhibit approximately 40°C higher clearing points and wider mesomorphic phase ranges compared with their hydrocarbon analogs 1c and 2c with a (CH2)4 spacer respectively. Compared to the corresponding ester-linked dimers 1a-c, three amide-linked dimers 2a-c exhibit 20°C higher clearing points upon cooling. The observation indicates not only that the introduction of the fluoromethylene spacer stabilised the mesophase in these discotic dimers, but also that the two interactions have synergistic effects on columnar packing in this system. Moreover, only amide-linked dimers exhibit good gelation property in a mixture of toluene and petrol ether, with a lower critical gelation concentration of 1.5 wt/vol%, thus indicating that gel formation occurred under the collaboration of hydrogen bonding and intrinsic π interactions in these dimers.

A wide range room temperature antiferroelectric liquid crystal mixture with moderate spontaneous polarization and sub-millisecond switching time

A room-temperature antiferroelectric liquid crystal (AFLC) mixture has been prepared by doping two chiral fluorinated compounds into a four-component achiral phenyl pyrimidine-based host matrix. The suitability of the mixture for practical applications has been tested by optical polarizing microscopy, synchrotron X-ray diffraction, frequency-dependent dielectric, and electro-optic studies. The mixture possesses an antiferroelectric phase over a wide temperature range (nearly 82 °C) followed by a paraelectric phase for 13.7 °C. It is found to display very fast switching between 243 and 45 μs at the driving voltage of 3.2 V/μm in the SmC*A phase. At 20 °C, the mixture exhibits a moderately high spontaneous polarization (137 nC/cm2), low viscosity (1.01 Pa s) and fast switching (240μs). The formulated mixture is thus expected to be suitable for use in fast-response AFLC-based display devices.

Perspective on structure-property relationship of room temperature single-component liquid crystals

ABSTRACT Ever since the serendipitous discovery of liquid crystals (LC) by Friedrich Reinitzer in 1888, a significant number of LCs have been synthesised and characterised. The ever-growing LCs emanating from conventional and non-conventional systems find applications in various electronic appliances such as flat-panel TV displays, notebooks, digital cameras, and domestic devices. The room temperature LCs (RT-LCs 20 to ±80 °C), either as single-component/composites, act as a starting point for such applications. Therefore, the quest for such RT-LCs is always valued and carved out as a promising niche for many such devices. Molecular design and the structure-property relationship are the recurrent themes for stable and single-component RT-LCs. The LC molecules starting from simple benzenoids to macrocycles with flexible hydrocarbon chains as spacer/terminal tails needed to be tethered in a precise pattern may lead to potential LCs. To craft stable and single-component RT-LCs, functional groups (nitrile, halogens, nitro, aldehydes, amine, thiol, alcohol, ketone, ester, amide) are frequently employed. RT-LCs with viscosity, dielectric, birefringence, and polarity enables the reduction of the number of components in a composites mixture. This review describes the genesis and importance of the single component RT-LCs, state-of-the-art LC research, perspectives, and new design strategies for venturing into a new horizon.

OPTIMIZATION OF THE DISPLAY PARAMETERS OF A ROOM TEMPERATURE LIQUID CRYSTAL "4-PENTYL-4'CYANOBIPHENYL" BY USING SINGLE-WALLED CARBON NANOTUBES

OPTIMIZATION OF THE DISPLAY PARAMETERS OF A ROOM TEMPERATURE LIQUID CRYSTAL "4-PENTYL-4'CYANOBIPHENYL" BY USING SINGLE-WALLED CARBON NANOTUBES

Remarkable Increase of Fluorescence Quantum Efficiency by Cyano Substitution on an ESIPT Molecule 2-(2-Hydroxyphenyl)benzothiazole: A Highly Photoluminescent Liquid Crystal Dopant

Fluorescent molecules with excited-state intramolecular proton transfer (ESIPT) character allow the efficient solid-state luminescence with large Stokes shift that is important for various applications, such as organic electronics, photonics, and bio-imaging fields. However, the lower fluorescence quantum yields (ΦFL) in the solution or viscous media, due to their structural relaxations in the excited state to reach the S0/S1 conical intersection, shackle further applications of ESIPT-active luminophores. Here we report that the introduction of a cyano group (-CN) into the phenyl group of 2-(2-hydroxyphenyl)benzothiazole (HBT), a representative ESIPT compound, remarkably increase its fluorescence quantum yield (ΦFL) from 0.01 (without -CN) to 0.49 (with -CN) in CH2Cl2, without disturbing its high ΦFL (=0.52) in the solid state. The large increase of the solution-state ΦFL of the cyano-substituted HBT (CN-HBT) is remarkable, comparing with our previously reported ΦFL values of 0.05 (with 4-pentylphenyl), 0.07 (with 1-hexynyl), and 0.15 (with 4-pentylphenylethynyl). Of interest, the newly-synthesized compound, CN-HBT, is miscible in a conventional room-temperature nematic liquid crystal (LC), 4-pentyl-4′-cyano biphenyl (5CB), up to 1 wt% (~1 mol%), and exhibits a large ΦFL of 0.57 in the viscous LC medium. A similar ΦFL value of ΦFL = 0.53 was also recorded in another room-temperature LC, trans-4-(4-pentylcyclohexyl)benzonitrile (PCH5), with a doping ratio of 0.5 wt% (~0.5 mol%). These 5CB/CN-HBT and PCH5/CN-HBT mixtures serve as light-emitting room-temperature LCs, and show anisotropic fluorescence with the dichroic ratio of 3.1 upon polarized excitation, as well as electric field response of luminescence intensity changes.

Potential liquid crystal-based biosensor depending on the interaction between liquid crystals and proteins

Liquid crystal biosensors serve an essential role to detect biomolecules and chemical events as an effective, simple and early detection tool. The detection of Human serum albumin protein by a room temperature liquid crystal 4́-pentyl-4-biphenylcarbonitrile has been investigated using multiple techniques such as Polarizing optical microscope, Raman spectroscopy and molecular docking. The dynamics of director transfigurations of the liquid crystal molecule in the presence of protein through interactions are reported in the study. The change in the alignment of liquid crystal molecules during the nematic phase is observed under a polarizing optical microscope. The interactions through which the liquid crystal molecules bind with protein is depicted from the docking analysis. The residues in the active sites confirm their presence from docking studies. The spectral behaviour has been investigated by temperature-dependent Raman spectroscopy. The findings from Raman spectra for the interaction between these compounds correlates with the residues confirmed from molecular docking analysis.

Amino Acid and Peptide-Based Liquid Crystals: An Overview.

The role of amino acids and peptides has found remarkable usage in both living systems and nonliving materials, which have enabled its utility by virtue of crafting molecular architectures through covalent bonds and non-covalent interactions. In material chemistry, the role of peptides in Liquid Crystals (LCs) is profound, especially in the rapid construction of supramolecular hierarchical networks. The importance of LCs for a variety of societal needs leads to the synthesis of innumerable LCs by conventional mesogenic strategy and nonconventional molecular design principles. For example, electronic appliances, including flat panel TV displays, electronic notebooks, digital cameras, domestic devices, use LCs as an integral component for such applications. In addition, LCs are useful in biological systems, including stem cell research, sensors for bacteria, virus, and proteins. These accomplishments are possible mostly due to the non-conventional molecular design principles for crafting LCs using smaller molecular motifs. The usage of amino acids and peptides in LCs facilitates many intrinsic characteristics, including side-chain diversity, chirality, directionality, reversibility, electro-optical, columnar axis, stimuli-responsive complex molecular architectures. The next essential criteria for any LCs design for useful applications are room temperature LC (RT-LC); therefore, the quest for such LCs system remains highly significant. Evidently, there are around half a million liquid crystalline molecules; only a handful of RTLCs has been found, as there is no simple, precise strategy or molecular design principles to obtain RT-LC systems. The smaller molecular motifs of amino acids and linear peptides as a structural part of mesogenic molecules led to many LC phases with properties, including lyotropic, thermotropic, and its applications in different realms. Therefore, this review serves as a compilation of Small Peptide-based LCs (SPLCs) exhibiting lyotropic and thermotropic phases with applications in the recent advancements.

Flavylium Salts: A Blooming Core for Bioinspired Ionic Liquid Crystals.

Thermotropic ionic liquid crystals based on the flavylium scaffold have been synthesized and studied for their structure‐properties relationship for the first time. The mesogens were probed by differential scanning calorimetry (DSC), polarizing optical microscopy (POM), and X‐ray diffraction (XRD). Low numbers of alkoxy side chains resulted in smectic (SmA) and lamello‐columnar (LamCol) phases, whereas higher substituted flavylium salts showed Colro as well as ordered and disordered columnar (Colho, Colhd) mesophases. Mesophase width ranged from 13 K to 220 K, giving access to room temperature liquid crystals. The optical properties of the synthesized compounds were probed towards absorption and emission properties. Strong absorption with maxima between 444 and 507 nm was observed, and some chromophores were highly emissive with quantum yields up to 99 %. Ultimately, mesogenic and dye properties were examined by temperature‐dependent emissive experiments in the solid state.

“Synthesis, Mesomorphic and DFT Studies of Chalcone Derived Room Temperature Liquid Crystal with Presence of Lateral Nitro and N, N-Dimethyl Amino Terminal Group”

In this present article, we wish to report on the liquid-crystalline properties of chalcone-ester based homologous series of compounds having aliphatic chain length in n-alkoxy group (n = 1 to 10, 12, 14, 16, 18). The present series consisted thirteen compounds, in which comp.C1 and C2 shows nonliquid crystalline properties, while comp.C3 to C7 display SmC phase and comp.C8 to C18 exhibits only nematic phase. Textural pattern of presently synthesized compounds are schlieren and threaded type. All this compounds were well characterized by elemental analysis, FT-IR and 1H NMR. Phase transition temperatures of present synthesised compounds were determined by optical polarising microscopy (POM), differential scanning calorimetric (DSC). Detailed XRD investigation endorses the presence of the nematic phase in higher homologues and SmC phase in lower homologues. It is shown that chalcone with ester as linking unit favors a calamitic liquid crystalline behaviour in molecules. To get more insights, the DFT based HOMO, LUMO studies are carried out which supports intramolecular charge transfer interactions in this class of mesogens. Chalconyl ester based compounds C3 to C12 shows antibacterial as well as antifungal activity compared with corresponding standard drugs.

Room-Temperature Columnar Liquid Crystals as Efficient Pure Deep-Blue Emitters in Organic Light-Emitting Diodes with an External Quantum Efficiency of 4.0%

A novel design of aggregation-induced emission (AIE) active columnar (Col) luminomesogens is reported, and they are demonstrated to act as highly efficient deep-blue emitters in organic light-emitting diodes (OLEDs). All derivatives exhibit Col liquid crystalline (LC) behavior at room temperature over a wide temperature range and desirable alignment properties, which is very important in using them as materials for organic electronic devices. These new AIE active luminomesogens were found to act as highly efficient emitters in OLEDs and unveiled a maximum external quantum efficiency of 4.0% for the first time in Col LCs with Commission International de l'E'clairage coordinates of (0.17, 0.07), which closely matches the National Television System Committee (NTSC) standard, corresponding to pure deep blue color. The detailed supramolecular assembly of the compounds has been characterized by modeling in the mesophase derived from small- and wide-angle X-ray scattering results.

The novel rufigallol-based liquid crystals with cholesterol units: synthesis, mesomorphic and photophysical properties

ABSTRACTThree novel rufigallol derivatives with four alkyl chains and two cholesteric units 6a, 6b and 6c were prepared in yields of 83–88%. The mesomorphic properties were investigated by DSC, POM and XRD analysis, suggesting that compounds 6a, 6b and 6c possess the ordered hexagonal columnar mesophase. The long alkyl chains contribute to the low phase transition temperature. Sample 6c with four dodecyl chains and two cholesterol units is a room temperature liquid crystal between 31°C and 87°C. Compounds 6a, 6b and 6c also have good fluorescence emission between 400 nm and 500 nm. The studies on CD spectra implied that the chiralities of cholesterol moieties are successfully transferred to the liquid crystalline core. Samples 6a, 6b and 6c are the first fluorescence liquid crystal based on rufigallol core with chiral cholesterol units.

Novel electron-deficient phenanthridine based discotic liquid crystals

Nitrogen-containing polycyclic core 5-phenylnaphtho[1,2,3,4-lmn] phenanthridine and its nitro-functionalized positional isomers were synthesized using Pictet-Spengler reaction between hexaalkoxytriphenylene-1-amine and various aryl aldehydes. The hexagonal columnar phase was observed in all the synthesized novel compounds. Mesomorphic characterization was carried out using conventional thermal analysis and X-ray diffraction techniques. These compounds showed room temperature liquid crystal phase and there is no crystalline phase observed even at −20 °C upon cooling from the isotropic temperature. Further, the long range of mesophase was confirmed by polarizing optical microscopy. Subsequently, charge transfer complexes were prepared by mixing the synthesized polycyclic hetero-aromatic compounds with 2,3,6,7,10,11-hexakis(octyloxy)-triphenylene. In UV–Vis absorption spectra, a redshift was found for the charge transfer complexes; which confirmed the interaction between donor-acceptor counterparts. The electrical conductivity of the charge transfer complexes and their pure target compounds was measured.