Liquid Crystalline Properties Research Articles

New alkoxyphenyl azomethine phenyl toluate liquid crystals

ABSTRACT A series of alkoxyphenyl azomethine phenyl toluates was synthesised and investigated for thermal and liquid crystalline behaviour. All the synthesised compounds were characterised using FT-IR, 1H NMR and 13C NMR spectroscopy. The materials demonstrated high thermal stability in thermogravimetric analysis (TGA), undergoing decomposition above 280°C. Mesomorphic properties were investigated using a combination of differential scanning calorimetry (DSC) and polarising optical microscopy (POM). All final compounds exhibited liquid-crystalline properties, displaying textures characteristic of calamitic liquid crystals. There was a tendency for lower homologs to display enantiotropic behaviour (N), while higher homologs exhibited dimesomorphic behaviour (N and SmC). The mesophases were confirmed through X-ray diffraction studies. A comparison with similar compounds revealed that interchanging the positions of methyl and alkoxy end groups influenced the nematic phase stabilities in lower homologues and led to a transition from SmA to SmC in higher homologues.

Synthesis and liquid crystal properties of a new class of calamitic mesogens based on twin 1,3,4-thiadiazole derivatives with imine linkage

The synthesis and characterization of two distinct novel series of compounds, [II]n and [V]n , containing 1,3,4-thiadiazole units, were studied in this work. The central core of the first series is phenyl, whereas the central core of the second series is OCH2CH2O. FTIR,1HNMR,13CNMR, and mass spectroscopy are used to characterize the materials used in this investigation. Liquid crystalline properties were confirmed by the use of differential scanning calorimeter (DSC) and hot-stage polarizing optical microscopy (POM). While other compounds showed no liquid crystalline behavior, the compounds [II]3 –[II]6 , [V]1 and [V]n showed enantiotropic nematic and smectic phases.

Palladium-Catalyzed Annulation Reaction of Bay-Diiodinated Arenes with o-Chloroaromatic Carboxylic Acids to Access Polycyclic Aromatic Compounds.

A palladium-catalyzed annulation reaction of bay-diiodinated arenes with o-chloroaromatic carboxylic acids was established. This approach enables the synthesis of a variety of polycyclic aromatic compounds, especially polyalkoxy-substituted polycyclic aromatic compounds, frequently found in discotic liquid-crystalline materials. The investigations indicate that the product 2,3,8,9,12,13-hexakis(hexyloxy)-5-azadibenzo[fg,op]tetracene demonstrates favorable room-temperature liquid-crystalline properties.

Quantum–Chemical Study of the Photophysical Behavior of Mesogenic Europium(III) Complexes with β‐Diketones and Lewis Bases

AbstractMetal‐containing liquid crystals such as Ln(III) complexes possess unique structural, liquid‐crystalline (LC), optical, and magnetic properties and represent modern cutting‐edge multifunctional materials. Application of mesogenic Ln(III) complexes is hindered by their nontrivial structure–property relationships. These relationships, in turn, depend on various factors, including insufficiently studied physicochemical processes. Although a proper Ln(III) element and the respective ligand environment are selected prior to synthesis of such complexes, the structural features of the coordination polyhedra, especially upon photoexcitation, are not uniquely defined. Therefore, this work focuses on the development of theoretical approaches to creating multifunctional materials represented by highly luminescent mesogenic Eu(III) complexes with β‐diketones and Lewis bases. The relationships between their structure, the parameters of Voronoi–Dirichlet polyhedra, the luminescence efficiency, and the LC properties were considered. The calculated excited states and intramolecular energy transfer rates were used to determine intramolecular energy transfer channels. The LC behavior of the studied materials was shown to mainly depend on the ligand environment, whereas their optical properties were found to be mostly governed by the coordination polyhedra.

Design of novel copper(I) metallomesogens with benzoylthiourea ligands having peripherally connected cyano or fluoro groups

A new set of liquid crystals based on copper(I) complexes with a cyano or fluoro group attached at the para position of an aromatic ring in a benzoyl thiourea ligand was prepared and studied for their liquid crystalline properties. Incorporating electron-withdrawing fluoro or cyano groups into the structural matrix can enhance their thermal stability, phase transition temperatures, and optical properties. The prepared Cu(Ln)2X compounds, where X = Cl, Br, or I, and 4-(dodecyloxy)-N-((4-fluorophenyl)carbamothioyl)benzamide (L1), N-((4-cyanophenyl)carbamothioyl)-4-(dodecyloxy)benzamide (L2), N-((4-fluorophenyl)carbamothioyl)-3,4-bis(octyloxy)benzamide (L3), and N-((4-cyanophenyl)carbamothioyl)-3,4-bis(octyloxy)benzamide (L4) displayed a SmA mesophase depending on the type of the attached terminal group (F or CN), number of alkoxy chains (one or two) and the nature of the halide ion coordinated to the metal center (Cl, Br or I). The structures of the compounds were characterized by 1H and 13C NMR, ESI-MS and IR studies, and their mesomorphic properties were investigated via a combination of polarising optical microscopy (POM), differential scanning calorimetry (DSC), and powder X-ray diffraction studies. These compounds were stable throughout the temperature range of the mesophases. This study further reiterates the consequential effect of incorporating cyano or fluoro groups on the mesomorphic and the size of the halide ions of the studied compounds.

Lyotropic Aqueous 2-Picolinium Ionic Liquid Crystals and Their Shear-Induced Foams.

1-Dodecyl-2-methylpyridinium bromide ([C12-2-Pic][Br]) and 1-hexadecyl-2-methylpyridinium bromide ([C16-2-Pic][Br]) are two ionic liquid crystals presenting thermotropic smectic phases above 80 °C. Aiming to take advantage of the liquid crystalline properties at lower temperatures, lyotropic aqueous systems were prepared from these two organic salts. Both systems were characterized by polarized optical microscopy (POM), X-ray powder diffraction (XRD), and fast field cycling nuclear magnetic resonance (FFC-NMR) relaxometry to assess their texture, phase structure, and molecular dynamics, respectively. The mesomorphic behavior was induced at room temperature. Moreover, the lyotropic [C12-2-Pic][Br]aq revealed a smectic phase with higher separation between layers, different from the lamellar phases found in the thermotropic system (S1 and SA), which is thermally stable up to 50 °C. Furthermore, the surfactant nature of the ionic liquids diluted solutions investigated in this work allowed the formation of foams. It was found that the precursor solutions of the lyotropic dilutions with the longest alkyl chain ([C16-2-Pic][Br]aq) originated liquid foams with more stable structures than those of [C12-2-Pic][Br]aq.

Study of mesomorphic, thermal and optical properties of 4-pentylbenzoic acid (5BA) and 4-n-alkyl-4́-cyanobiphenyl (nCB; n = 5, 6) supramolecular hydrogen bonded mesogenic complexes

Within the scope of this study, the process of producing and analyzing a liquid crystalline substance (supramolecular hydrogen-bonded mesogen) is presented. The formation of this mesogen involves the use of two chemicals, namely 4-pentylbenzoic acid (5BA) and 4-n-alkyl-4́-cyanobiphenyl (nCB; n = 5, 6). Equimolar (1:1) 5BA/5CB and 5BA/6CB binary combination samples have been organized by using one at a time mixing 5CB and 6CB liquid crystal chemical substances with 5BA. Differential scanning calorimetry (DSC) and polarized optical microscopy (POM) are employed for the examination of phase transitions, and liquid crystalline phase texture properties of the produced mesogens. The phase transformation sequence that occurred during heating and cooling is Crystal (Cr) ↔ Smectic A (SmA) ↔ Nematic (N) ↔ Isotropic (I) with the 1st order or weakly 1st order transition. The nematic range value observed for 5BA/6CB is considerably smaller than the nematic range value observed for 5BA/5CB, but the thermal mesophase range value for both is approximately the same. Fourier-transform infrared (FTIR) evaluation of 5BA, 5CB, and their hydrogen-bonded combos (5BA/nCB; n = 5, 6) confirmed attribute peaks. The X-ray diffraction (XRD) study revealed that the produced mesogens possess a crystalline structure. In addition, UV–Vis experiments demonstrated that the increase in alkyl chain length in the combination resulted in a decrease in absorbance and wavelength values, while leading to an increase in absorbency and band gap energy values. These results propose workable purposes for the synthesized substances in liquid crystal displays and other optoelectronic devices. Overall, the findings display the feasibility and viability of these novel hydrogen-bonded liquid crystalline mesogens in various technological applications.

Synthesis and Characterization of Azo-Based Cyclotriphosphazene Compounds: Liquid Crystalline and Dielectric Properties

Synthesis and Characterization of Azo-Based Cyclotriphosphazene Compounds: Liquid Crystalline and Dielectric Properties

Optical maneuvering of photofunctioning hybrid perovskite for future photonics potential application

Hybrid perovskites, known for their multidimensional opto-electronic properties and capability to generate multi-color emission bands, are highly sought after for light-emitting devices due to their liquid crystalline behavior in the solution phase. This behavior enables easier ion mobility, facilitating ion exchange processes. Exploiting the liquid crystalline properties of perovskites, we applied a halogen exchange reaction in the solution phase using tightly focused laser trapping techniques. Our study demonstrates the successful development of high-luminescent bulk single crystals of methylammonium lead halide alloy MAPb(Br/I)3, which exhibit multi-color emission capabilities, underscoring their potential for optoelectronic applications. We fabricated bulk single crystals of MAPbBr3, measuring 20 × 20 μm2, displaying bright green luminescence. Using a tightly focused trapping laser beam (1064 nm, 1 Watt) with a high numerical aperture (0.9, 60X objective lens), we irradiated a specific area of the green luminescent MAPbBr3 single crystal immersed in a 200 μM methylammonium iodide (MAI) solution for 30 min at room temperature. This treatment induced a red emission band at 605 nm at the irradiated location, while surrounding areas retained the original green luminescence. In a parallel experiment, increasing the iodide concentration to 300 μM caused the emission color of a similar-sized crystal to change uniformly from green to red. Photoluminescence spectroscopy and EDS confirmed the halide exchange from MAPbBr3 to MAPbBr2.3I0.7. This method, influenced by laser parameters such as power, wavelength, and aperture, provides new opportunities for multi-color emission patterning and offers significant insights for advancing optoelectronics.

Probing the mesophase formation in thermotropic liquid crystal HBDBA using temperature-dependent Raman spectroscopy and DFT method

Liquid crystalline properties of the synthesized liquid crystal (LC) N-(o-hydroxybenzylidene)-N′-(4-n-alkoxybenzylidene) azines (HBDBA) are probed thoroughly using the comprehensive array of techniques e.g. differential scanning calorimetry (DSC), differential thermal analysis (DTA), polarizing optical microscopy (POM), temperature-dependent Raman spectroscopy and density functional theory (DFT) method. In this study, intricate molecular interactions crucial for mesophase formation of liquid crystalline system HBDBA and molecular rearrangement that occurs during LC transitions are unravelled comprehensively. Remarkably, at the Cr → SmA phase transition, the peak position, linewidth, and intensity of signature Raman bands are prominently changed. A thorough analysis of Raman marker bands and DFT calculation confirm the disruption of intramolecular hydrogen bonds in HBDBA at the Cr → SmA transition. The conclusion of the present study enriches the understanding of the underlying mechanisms of mesophase formation and intricate molecular interactions and arrangement at the molecular level of the thermotropic LC.

Metal-induced self-assemble transition: Triple responses on photophysical, liquid crystalline and gel properties of Hg(II)-coordination tetraphenylene dimer

The metal-coordination self-assemble system played an important role on constructing novel supramolecular smart-response materials. Although the single and double-response materials based on metal-induced self-assembly had been studied extensively, the triple responses for this kind of supramolecular material was seldom reported. In this work, the first metal-induced self-assemble system with triple responses on photophysical, liquid crystalline and gel properties was presented based on Hg2+-coordination tetraphenylene dimer (Bis-TPE). Bis-TPE was prepared by bridging two alkyl-substituted tetraphenylene with amido chain. It possessed the fluorescence response from the strong emission for Bis-TPE to the faint emission for Bis-TPE-Hg2+ complex. The self-assemble mechanism of Bis-TPE-Hg2+ was clarified as that Hg2+ was located in the cavity of the amido-ether chain of Bis-TPE. The Hg2+-induced mesomorphic transition was also observed from smectic mesophase for Bis-TPE to hexagonal columnar mesophase for Bis-TPE-Hg2+ complex. The unique Hg2+-induced gel transition was further distinguished from low-order spherical morphology for Bis-TPE to high-order fibrous morphology for Bis-TPE-Hg2+ complex. The maximum fluorescence wavelength exhibited the giant shift from 494 nm for Bis-TPE in gel to 606 nm for Bis-TPE-Hg2+ in gel. This kind of triple responses on photophysical, liquid crystalline and gel properties for metal-coordination self-assemble system was described for the first time, affording a new idea on design of new multiple-response materials with unique properties.

Synthesis and liquid crystalline properties of novel series containing 5H-thiazolo[3,4-b][1, 3, 4]thiadiazole unit with schiff base and azo linkage

Two series were synthesized containing a 5H-thiazolo[3,4-b][1, 3, 4]thiadiazole unit with a Schiff base and an azo linkage. Polarized optical microscope (POM) and differential scanning calorimetry (DSC) were used to examine the mesomorphic behavior. Enantiotropic nematic phases were present in compounds with alkoxy terminal groups of n = 1–4 methylene units for both series. While enantiotropic smectic A (SmA) is also present in molecules with n = 6–8 carbon atoms in addition to nematic phases for a series of azo linkage. The molecules in the Schiff base linkage series with n = 6–8 exhibited pure smectogenic liquid crystalline behavior.

Pluronic P123/DMSO Lyotropic Liquid Crystal for Incorporating Bioactive Substances for Topical Application.

Lyotropic liquid crystals (LLCs) have attracted considerably growing interest in drug delivery applications over the last years. The structure of LLC matrices is complementary to cell membranes and provides an efficient, controlled, and selective release of drugs. In this work, a complex of experimental methods was used to characterize binary LLCs Pluronic P123/DMSO and triple LLC systems Pluronic P123/DMSO/Ibuprofen, which are interesting as transdermal drug delivery systems. Liquid crystalline, thermal, and rheological properties of LLCs were studied. Concentration and temperature areas of the lyomesophase existence were found, and phase transition enthalpies were evaluated. Intermolecular interactions among the components were studied by infrared (IR) spectroscopy. In vitro studies of Ibuprofen (Ibu) release from various LLCs allow differentiation of its release depending on the polymer content. Atomic force microscopy and contact angle methods were used to characterize the surface morphology of the hydrophobic membrane, which was used as a stratum corneum model, and also evaluate the adhesion work of the LLCs. A complex analysis of the results provided by these experimental methods allowed revealing correlations between the phase behavior and rheological characteristics of the LLCs and release kinetics of ibuprofen. The proposed biocompatible systems have considerable potential for a transdermal delivery of bioactive substances.

Synthesis, characterization and investigation of liquid crystalline properties for some cross-link polymers containing melamine

Synthesis, characterization and investigation of liquid crystalline properties for some cross-link polymers containing melamine

Synthesis and characterization of grafted graphene oxide materials with lyotropic liquid crystalline properties detected by NMR spectroscopy

Grafted derivatives of graphene oxide (GO), namely N-vinyl-2-pyrrolidone grafted-GO (GO-g-NVP) and oleic acid grafted-GO (GO-g-OLA) were prepared by heating GO in the presence of the corresponding vinyl monomers and the AIBN radical initiator. The lyotropic mesogenic behavior of GO-g-NVP and GO-g-OLA in DMSO‑d6 was proved by deuterium NMR spectroscopy, showing these materials could be used as alignment media for obtaining NMR anisotropic parameters in organic solvent.

Controlling the Nematic Liquid Crystallinity of Cellulose Nanocrystals with an Alcohol Ethoxy Sulfonate Surfactant.

Cellulose nanocrystals (CNCs) are biobased colloidal nanorods that have unlocked new opportunities in the area of sustainable functional nanomaterials including structural films and coatings, biomedical devices, energy, sensing, and composite materials. While selective light reflection and sensing develop from the typical chiral nematic (cholesteric, Nem*) liquid crystallinity exhibited by CNCs, a wealth of technologies would benefit from a nematic liquid crystal (LC) with CNC uniaxial alignment. Therefore, this study answers the central question of whether surfactant complexation suppresses CNC chirality in favor of nematic lyotropic and thermotropic liquid crystallinity. Therein, we use a common surfactant having both nonionic and anionic blocks, namely, oligo(ethylene glycol) alkyl-3-sulfopropyl diether potassium salt (an alcohol ethoxy sulfonate (AES)). AES forms complexes with CNCs in toluene (a representative for nonpolar organic solvent) via hydrogen bonding with an AES' oligo(ethylene glycol) block. A sufficiently high AES weight fraction endows the dispersibility of CNC in toluene. Lyotropic liquid crystallinity with Schlieren textures containing two- and four-point brush defects is observed in polarized optical microscopy (POM), along with the suppression of the cholesteric fingerprint textures. The results suggest a nematic (Nem) phase in toluene. Moreover, thermotropic liquid crystallinity is observed by incorporating an excess of AES, in the absence of an additional solvent and upon mild heating. The Schlieren textures suggest a nematic system that undergoes uniaxial alignment under mild shear. Importantly, replacing AES with a corresponding nonionic surfactant does not lead to liquid crystalline properties, suggesting electrostatic structural control of the charged end group of AES. Overall, we introduce a new avenue to suppress CNC chirality to achieve nematic structures, which resolves the long-sought uniaxial alignment of CNCs in filaments, composite materials, and optical devices.

Size-dependent optical and dielectric anisotropy of CdS nanowire doped high-birefringent nematic liquid crystalline compound

Highly birefringent liquid crystals have grabbed ample attention because of their potential applications as an active medium for devices in visible, infrared and other spectral regions. Here, we have attempted to study the effect of the size and concentration of CdS nanowires on a nematic liquid crystal. Anisotropy in liquid crystals is one of those distinguishing traits that gain their superiority over other materials. We hereby have analyzed how optical and dielectric anisotropy respond to variations in the size and concentration of the dopant. The study is of significant scientific value because there is very little literature available on how dopant size can alter liquid crystalline properties and also introduces a method to tune the properties of pure liquid crystals (LCs) by varying the size and concentration of the dopant. The study explains how the size of the nanowires changes the analyzed parameters and up to what extent. The obtained results yield a significant increase in both optical and dielectric anisotropy by doping CdS nanowires making them an excellent choice for dopant selection. CdS-doped nematic LC mixtures have proved to be highly birefringent and possess a high positive dielectric anisotropy as well. Such a compound can be of great application in device fabrications such as laser beam steerers, electronic lenses, attenuators and light shutters, etc.

Naphthalene-based symmetrical liquid crystalline dimers: Synthesis, characterization, mesomorphic behaviour and DFT studies

The reactions of different α,ω-dibromo alkanes with (E)-4-(naphthalen-2-yldiazenyl)phenol and (E)-4-(naphthalen-2-ylimino)methyl)phenol, respectively, led to the synthesis of two new homologous series of liquid crystalline symmetrical dimers with azobenzene or azomethine central linkage and containing the naphthalene moiety as a rigid core. Spectroscopic techniques like FT-IR, 1H NMR, 13C NMR and elemental analysis confirmed their structure. These dimers exhibited mesomorphic phases, studied through POM and DSC. Their photophysical behaviour was explored using UV–visible spectroscopy. Remarkably, dimers with even spacer units (n = 2, 4, 6, 8, 10, 12) displayed excellent liquid crystalline properties as nematic phases, with extended mesophase lengths and thermal stability for both series. The study revealed the vital role of spacer length in determining liquid crystalline behaviour. The computational studies employed the B3LYP method and electron density method for optimization.

Revisiting Dimorphs of 4-n-octyloxybenzoic Acid: Contrasting Mechanical Property and Surface Wettability.

4-n-octyloxy benzoic acid is known to exhibit liquid crystalline properties, and under normal pressure and temperature conditions, it exists as at least two crystalline polymorphs. We revisited the system and discovered that single crystals of one of the polymorphs display plastic deformation, whereas the other is brittle. n-octyl chains are arranged in an end-to-end fashion, forming slip planes in the plastically deformable polymorph, whereas they are interdigitated in the crystal structure of the brittle polymorph. Due to the difference in the arrangement of the -COOH group and alkyl chains, the major faces of the crystals of both polymorphs possess significant differences in the wettability towards moisture.

Palladium-Catalyzed Annulative π-Extension of Bay-Iodinated Triphenylenes to Access Polycyclic Aromatic Compounds.

A palladium-catalyzed annulative π-extension reaction of bay-iodinated triphenylenes with aryl iodides/o-chloroaromatic carboxylic acids was developed. This approach enabled the synthesis of diverse polycyclic aromatic compounds, including dibenzo[fg,op]tetracenes, azadibenzo[fg,op]tetracenes, and tribenzo[a,g,m]coronenes. Initial studies indicate that the resulting product, 2,3,8,9,14,15-hexakis(decyloxy)tribenzo[a,g,m]coronene, exhibits good liquid-crystalline properties.