Mesophase Behaviour Research Articles

Synthesis of new liquid crystal Schiff's bases bearing ester moiety, DFT calculation and mesomorphic studies

A new homologues series of liquid crystalline material (E)-4-(((3,4-dimethylphenyl) imino) methyl) phenyl4-n-alkoxybenzoate (SBn) synthesized. SBn compounds was subjected to analysis using infrared spectroscopy, proton magnetic resonance, 13C NMR, UV- visible and mass spectroscopy for characterization. The investigation of liquid crystalline phases and their transition enthalpies was carried out using a polarized optical microscope and differential scanning calorimetry, respectively. All compounds within the homologous series display mesogenic properties. The SB1 -SB7 homologues exhibit an enantiotropic nematic mesophase within the temperature range of 180–106 °C, while the SB14 -SB18 homologues show a smectic A mesophase at temperatures between 78 and 75 °C. Additionally, the SB8 -SB10 homologues exhibit a monotropic smectic A mesophase at 61–59 °C. The phase transitions observed in series SBn are compared with those of structurally related compounds to assess the influence of central linkage and lateral tail `substitution on their mesophase behavior. With the help of DFT; EHOMO and ELUMO energy gap were computed to be negative for all derivative molecules, indicating their stability and in the following order: SB4 > SB6 > SB8 > SB12. Dielectric through determined values of complex permittivity of the synthesised liquid crystal over a broad frequency range are reported. Determined static permittivity value of liquid crystal is 2.25, at room temperature. The compound SBn exhibited a relaxation peak in the dielectric loss spectra in the microwave frequency range, which may be assigned to the rotation of the end polar group of the molecule.

Mesophase Behavior of Molecules Containing Three Benzene Rings Connected via Imines and Ester Linkages.

Ten new compounds based on the methineazo-azomethine (CH=N-N=CH) and ester linking groups were prepared and investigated for their mesophase behavior and optical stability, and liquid crystals of 4-substituted phenyl methineazo-azomethine phenyl 4-alkoxybenzoates, I n a-e , were investigated. An alkoxy group with a length between 8 and 12 carbons is attached to the phenyl eater wing, while the other terminal ring is substituted in its 4-position with one of the polar NO2, F, Cl, CH3O, and N(CH3)2 groups. The molecular structures of the newly prepared compounds were verified by using 1H NMR, 13C NMR, and elemental analysis. Differential scanning calorimetry and polarized optical microscopy were applied to investigate their mesophase behavior. All members of the prepared homologous series showed excellent thermal mesomorphic stability over wide temperature ranges. The geometrical and thermal properties of the investigated compounds were verified via density functional theory (DFT). The theoretical results revealed that all of the compounds are almost planar. Finally, the experimentally established values of the mesophase data were correlated with the predicted quantum chemical characteristics evaluated by DFT.

Triphenylene diimides: A new class of discotic liquid crystals

Unlike the well-explored perylene diimides and naphthalene diimides, the synthesis and characterization of triphenylene diimides have not been reported to date. In this study, several di(decyloxy)-substituted triphenylene 2,3,6,7-tetracarboxyldiimides with various imide substituents were synthesized and comprehensively analyzed for their photochemical properties and mesophase behavior. It was observed that different imide substituents significantly affect self-assembly in both solution and the liquid-crystalline state. Specifically, diimide 2–1, with two n-octyl chains at the imide nitrogens, exhibits a tendency to self-assembly at relatively high concentrations in CDCl3 and displays a hexagonal columnar (Colh) phase near room temperature. Remarkably, its isomer, diimide 2–2, with two branched 2-ethylhexyl chains, exhibits an enatiotropic Colh phase with an unusually large range of 292 °C, extending from 7 °C to 299 °C. Furthermore, the study also reports two triphenylene monoimide diesters as room temperature liquid crystals, each composed of one imide, two alkoxycarbonyl, and two alkoxy side chains. These findings not only enrich the diversity of aromatic diimides but also highlight the potential applications of these novel diimides in the field of liquid crystals.

Synthesis, mesophase behavior, and computational studies of dimers composed of three-ring rod-shaped ester-imine linkage monomeric unit

New symmetrical liquid crystal dimers composed of three-ring ester imine rod-shaped monomers with flexible alkyl chains of different parity were synthesized. The thermal stability of the newly synthesized compounds was determined using thermogravimetric analysis. The phase transition and mesogenic behavior of the compounds were explored using polarising optical microscopy and differential scanning calorimetry. Dimers with odd parity spacers exhibited the phase sequence Iso-N-Nx-SmX-Cr. The Nx phase transition was observed by polarising optical microscopy. This transition was distinct from that of the uniaxial nematic phase. The Nx phase was absent in the dimer with even parity spacers. A density functional theory study was carried out to investigate the stable configuration and influence of the solvent on the structural parameters, chemical reactivity parameters, and excited state properties of the molecules.

Tailoring the dielectric and ferroelectric response of mixtures containing bent-core liquid crystals through light-irradiation and composition

We report the mesomorphic behaviour, dielectric and ferroelectric properties, and computational modelling of binary mixtures containing two bent-core liquid crystals: the so-called NG75-COO (3,4́- Bis[4-(4-n-tetradecyloxybenzoyloxy)benzoyloxy]biphenyl), which forms smectic phases, and IP31- AzB (3,4′ - Bis[4-(4-n-tetradecyloxyphenylazo)benzoyloxy]biphenyl), which forms columnar phases. The phase diagram, assessed by polarised optical microscopy, shows that the binary mixtures retain the mesophase behaviour of the major component, whilst the equimolar mixture displays smectic-type phases. Dielectric and ferroelectric analyses were carried out on samples containing 10%, 50%, and 90% of IP31-AzB (molar %), and we also investigated structure–property correlations by differential functional theory. The NG75-COO/IP31-AzB mixtures undergo strong dielectric and ferroelectric response due to the presence of highly polarisable groups in the bent-core components, particularly at the ester groups. All the mixtures under study exhibit light-responsiveness induced by reversible E-to-Z photoisomerization (trans-to-cis) of the azobenzene group in IP31-AzB, together with an increase in the molecular dipole moment. The potential to tune the phase behaviour of the mixtures, as well as their dielectric and ferroelectric responses, are investigated by light irradiation under different conditions of intensity and temperature.

Effect of Laterally Substituted Methoxy Group on the Liquid Crystalline Behavior of Novel Ester Molecules

Background: The aim of this research is to study the effect of length-to-width ratio on mesomorphism to enhance the understanding of its potential applications. This will be achieved by synthesizing a unique and innovative series of identical ester molecules, including lateral methoxy groups and terminal ethyl benzoate groups. In this research, we aim to find new insights into the relationship between molecular structures and mesomorphic behaviors, which could have significant implications for the development of advanced materials with adapted properties. : The objective of the study is to investigate the mesophase behavior of new ester mesogens and determine how they are influenced by lateral methoxy groups. By identifying the underlying perspectives and relationships between these variables, we hope to better understand the unique properties and potential applications of these materials. Method: In this research work, the focus is on the synthesis of ethyl(E)-4-((3-(4-alkoxy-3- methoxyphenyl)acryloyl)oxy)benzoate, which is prepared from Steglich esterification method by using (E)-3-(4-alkoxy-3-methoxyphenyl)acrylic acid and ethyl 4- hydroxybenzoate. Synthesis processes involve precise reaction sequences designed to ensure maximum yield and purity of the final product. By providing a detailed report on the experimental process, this study contributes to the ongoing research efforts aimed at the development of innovative compounds with various applications in liquid crystals Result: A new set of liquid crystal derivatives has been synthesized and studied to investigate the effect of molecular structure on the behavior of liquid crystals, with particular attention to the group -OCH3 located laterally. This series was composed of 12 derivatives (C1-C16). Among them, the first six derivatives (C1-C6) did not have the characteristics of a liquid crystal, while the remaining derivatives (C7 and C8) had a monotropic behavior, and C10-C16 had an enantiotropic smectogenic liquid crystal behavior without exhibition of the nematic phase. The average thermal stability of the smectic property was 87.33 °C, and the mesophase range was 2 °C to 14 °C. The molecular structure was confirmed by analytical and spectral analysis. The properties of liquid crystals of this new series were compared with those of other known structurally similar homologous series. The transition temperatures were determined with an optical polarizing microscope equipped with a heating phase. Conclusion: The mesomorphic thermal and optical properties of the compounds have been validated by DSC and POM techniques. The result shows that the length of the alkyl chain has a significant influence on the mesomorphic characteristics and thermal stability of the different mesophases. Evaluation of the compounds studied indicates that the molecules are sensitive to their lateral substituent, which influences the thermal characteristics and stability of the mesophase.

Mesomorphism of imidazolium-based fluorinated ionic liquids

Ionic liquid crystals have received increasing interest due to their positional and/or orientational order as well as the freedom in molecular motions that arise from the formation of mesophases between solid and liquid. While phase changes of non-fluorinated ionic liquids have been widely reported, there have been few reports on the temperature-dependent phase behavior of fluorinated ionic liquids. Here, we present a series of fluorinated ionic liquids with methylimidazolium cations bearing 1H, 1H, 2H, 2H-perfluoroalkyl chains (butyl, hexyl, and octyl) and halide counterions, and demonstrate their thermotropic mesomorphism. These cations were synthesized under solvent-free conditions, and anion exchange was used to vary the halide counterion. The thermal behavior of the compounds was studied using thermogravimetric analysis and differential scanning calorimetry, revealing both liquid crystalline phases and solid-solid phase transitions. We discovered that the mesomorphic properties of the ionic liquids depend strongly on the length of the perfluoroalkyl pendants. Specifically, ionic liquids with a fluorinated butyl chain showed no mesophase behavior while those with hexyl and octyl fluorinated chains displayed liquid crystalline phases at temperatures above 100 °C. The mesophases were further characterized by polarized optical microscopy and powder X-ray diffraction, highlighting the impact of the fluorinated alkyl chain length.

Detailed investigations on hydrogen bond liquid crystals formed between 4-nitrobenzaldehyde and alkyloxy benzoic acids

Eight mesogenic liquid crystalline complexes are formed between 4-Nitrobenzaldehyde and p-n alkyloxy benzoic acids whose carbon number varies from pentyl to dodecyl. Chemical, optical and thermal investigations are carried out to all the mesogenic complexes in order to establish the intermolecular hydrogen bonding, mesophase formation, their transition temperatures, enthalpy values, order of transition, thermal equilibrium, thermal stability factor, behavior of mesophases with respect to temperature and specific heat capacity. All the investigations details the chemical, optical and thermal properties possessed by the mesogenic complexes which make them for the apt applicational viability.

Quantum-Chemical Approaches to Creation of Mesogenic Binuclear Europium(III) Complexes with Intensive Luminescence

This article contains data on the application of quantum-chemical methods for simulation of mesogenic binuclear complexes of europium(III) (Eu(III)) with substituted β-diketones and Lewis bases along with the possibility of prediction of their liquid crystalline (LC) properties. The relationships between geometric parameters of the complexes' molecules, the structural features of their coordination polyhedra and the probability of mesophase behavior were considered. According to the calculated parameters of Voronoi-Dirichlet polyhedra, the structural features of the first coordination sphere of Eu(III) complexes were studied and compared with the data for mononuclear complexes. Using the calculated energies of the ligands' excited states, the luminescence efficiency of the complexes was estimated. The results of quantum-chemical simulations provide recommendations for selection of ligand environment for the synthesis of LC binuclear Eu(III) complexes.

TGBs below SmA*: Mesophase behaviours and optical properties

Re-entrant mesophase behaviours are studied including the relaxation effect of TGB phases, and an abnormal phase transition of TGBC*-SmA*. For the re-entrant TGBA mesophase between SmA* and TGBC*, its temperature range can be expanded by doping method and meanwhile its selective reflection wavelength moves to the visible light range. Furthermore, this series of dimers are compared with other series to study the structure–property relationship. This research provides an important reference for preparing materials exhibiting multiple mesophases that reflect visible light within multiple temperature ranges.

Cycloplatinated(II) metallomesogens and their binary-mediated chirality transfer and amplificated deep-red circularly polarized luminescence with ultrahigh dissymmetry factor over 0.13

Incorporating supramolecular chirality and high emission into metallomesogens has great significance in the field of flexible electronic devices because of their emergent capacities for enlarged chiroptical activities and either thermotropic or solution-processability. In this work, an enantiomeric pair of chiral Pt(II) metallomesogens (S)/(R)-Pt1 were prepared through laboratory-synthesized chiral picolinic acid ligands and phenylpyridine derivatives to study their mesophase behaviors, chiroptical properties, and chirality transfer and amplification. The solutions of (S)/(R)-Pt1 emitted green phosphorescence at 508 nm, but the amorphous form displayed orange-red phosphorescence at 616 nm. Upon gentle grinding or heating, the emission color of Pt1 was dramatically changed with a bathochromic shift of 47 and 51 nm, respectively, because of emerged intermolecular π···π and Pt⋯Pt interactions in all aggregation states. Furthermore, the chiroptical properties and LC self-assembly model were proposed by Density Functional Theory (DFT) calculations and chiroptical spectrum measurements. The enantiotopic (S)/(R)-Pt1 complexes exhibited electronic circular dichroism (CD) and circularly polarized luminescence (CPL) activities in solution with a smaller asymmetry factor (±5 × 10−4) by chiral disturbance. This pair of exclusively enantiomeric complexes exhibited smectic mesophase behavior in the range of 31.4–76.5 °C but induced unsuccessfulness of helical packing in LC states due to weak induction ability. Contrastively, binary-component mediated supramolecular helical formation and amplificated deep-red CPL switch with ultrahigh dissymmetry factor over ±0.13 in helical twist grain boundary phases (TGBA*) mesophase has been realized.

The influence of mannose-based esters on the mesophase behaviour of lyotropic liquid crystalline nanosystems as drug delivery vectors

Lyotropic Liquid Crystalline (LLC) nanoparticles represent an emerging class of smart, biocompatible, and biodegradable systems for the delivery of drugs. Among these, structures with complex 3D architectures such as cubosomes are of particular interest. These are non- lamellar assemblies having hydrophobic and hydrophilic portions able to carry drugs of different nature. They can further be modulated including suitable additives to control the release of the active payload, and to promote an active targeting. Starting from monoolein (GMO) cubic phase, different concentrations of mannose-based esters were added, and the eventual structural modifications were monitored to ascertain the effects of the presence of glycolipids. Moreover, the structural properties of these nanosystems loaded with Dexamethasone (DEX), a very well-known anti-inflammatory steroid, were also studied. Experiments were carried out by synchrotron Small Angle X-ray Scattering (SAXS), Raman Microspectroscopy (RMS) and Attenuated Total Reflectance-Fourier Transform Infrared (ATR-FTIR) measurements. The drug delivery potential (i.e. entrapment efficiency and release properties) of the obtained nanoparticles was evaluated. Finally, in vitro cytocompatibility and anti-inflammatory activity studies of the prepared formulations were carried out. Inclusion of mannose-based surfactants up to 10 mol% influenced the structural parameters of Im3m cubic phase and swollen cubic phases were obtained with the different glycolipids with lattice parameters significantly higher than GMO. A complete cytocompatibility and an increased DEX activity were observed, thus suggesting the possibility to use GMO/glycolipids nanoparticles to formulate innovative drug delivery systems.

Development of a novel lipid for the in meso crystallisation and structure determination of membrane proteins and the impact of 2-MAG on mesophase behaviour

Development of a novel lipid for the <i>in meso</i> crystallisation and structure determination of membrane proteins and the impact of 2-MAG on mesophase behaviour

The influence of the ring system with mono/diester and imine links, and terminal unsaturated carbon chains on mesomorphism and their quantum-mechanical study

ABSTRACT Five homologous series of low molar mass liquid crystals containing mono/diester and imine-linked cores with terminal unsaturated carbon chains and/or a carboxylic group were synthesised. They were characterised with IR, UV and 1H-NMR spectroscopies. Liquid crystalline properties of all the derivatives were studied by polarised optical microscopy and their mesophase transition enthalpies and entropy changes measured by DSC. The 4-((4-n-alkoxybenzoyl) oxy) benzoic acids (n OPBA) exhibit enantiotropic smectic A and nematic mesophases, while all the 4-allyl-2-methoxyphenyl 4-n-alkoxybenzoates (n OBEg) and 4-allyl-2-methoxyphenyl (E)-3-(4-n-alkoxyphenyl) acrylates (n OCEg) do not show any liquid crystalline properties. Intermediate members of the 4-allyl-2-methoxyphenyl (E)-4-((4-n-alkoxybenzylidene) amino) benzoate series (n OPMABEg) and the 4-((4-allyl-2-methoxyphenoxy) carbonyl) phenyl 4-n-alkoxybenzoate series (n OB2Eg) exhibited only enantiotropic nematic mesophase behaviour. The optimised geometry of all the liquid crystalline compounds was calculated by density functional theory (DFT), and the effect of the twist angle ϴ of the ring system, the length of the core, HOMO-LUMO energies and electrostatic potential of the compounds on mesomorphism was examined. The effects of the linking groups, the ring systems, the length of the core and the terminal unsaturated carbon chain on mesophase behaviour were studied. The mesophase transitions of the five series were compared with each other and with structurally similar compounds to evaluate the effects of the ring systems on their mesophase behaviour.

Molecular Rearrangements in Protomembrane Models Probed by Laurdan Fluorescence.

Lipid membranes are a key component of living systems and have been essential to the origin of life. One hypothesis for the origin of life assumes the existence of protomembranes with ancient lipids formed by Fischer-Tropsch synthesis. We determined the mesophase structure and fluidity of a prototypical decanoic (capric) acid-based system, a fatty acid with a chain length of 10 carbons, and a lipid system consisting of a 1:1 mixture of capric acid with a fatty alcohol of equal chain length (C10 mix). To shed light on the mesophase behavior and fluidity of these prebiotic model membranes, we employed Laurdan fluorescence spectroscopy, which reports on the lipid packing and fluidity of membranes, supplemented by small-angle neutron diffraction data. The data are compared with data of the corresponding phospholipid bilayer systems of the same chain length, 1,2-didecanoyl-sn-glycero-3-phosphocholine (DLPC). We demonstrate that the prebiotic model membranes capric acid and the C10 mix show formation of stable vesicular structures needed for cellular compartmentalization at low temperatures only, typically below 20 °C. They reveal the fluid-like lipid dynamic properties needed for optimal physiological function. High temperatures lead to the destabilization of the lipid vesicles and the formation of micellar structures.

Imine based Four-Ring Chalcone-Ester liquid Crystals: Synthesis, Characterization, mesomorphic behaviour and DFT approach

In this study, new imine-based chalcone-ester liquid crystals with symmetric and unsymmetrical alkoxy chains were synthesized and their mesomorphic behaviour was examined. The FT-IR, 1H NMR, 13C NMR, and mass spectral analysis have all been used to characterize new mesogens. From the study of mesophase behaviour, the compounds of CHE-(6–18) and 12-CHE-(6–18) series with different alkoxy chains at both the ends exhibited stable enantiotropic smectic C in addition to nematic mesophase for compounds with longer alkoxy chains. Whereas the three compounds of CHAE series were found to be non mesogenic. By comparing new compounds with structurally similar compounds, the impact of inclusion/replacement of various mesogenic units have been discussed. The theoretical calculations were performed to illustrate the mesomorphic behaviour of the studied compounds in terms of aromaticity and π–π stacking. Also, the experimental findings of the individual compounds were correlated with the calculated polarizability, dipole moment, and aspect ratio. Moreover, a projection of the molecular electrostatic potential and the frontier molecular orbitals has been considered to demonstrate the influence of the polarity of the terminal chains and the mesogenic cores on the energy gap of the FMOs and the distribution of electrostatic charges on the investigated compounds.

The effect of position of (-)-menthyl on the mesomorphic and photoisomerization behavior in azobenzene chiral liquid crystals

As the mesomorphic type of liquid crystals could be largely altered by the molecular chirality, we herein explored the effect of position of chiral (-)-menthyl on the mesomorphic and photoisomerization behavior in azobenzene liquid crystals. By modifying the position of chiral (-)-menthyl in the menthol based liquid crystal compounds through gradually increasing the alkyl chain length of the dicarboxylic spacer, seven new chiral liquid crystal compounds 4-(4-menthyloxy-n-oxoalkanoyloxy)-4′-(4-ethoxybenzoyloxy) azobenzene MnAZO2B (n = 2–8) were prepared. A combination of analysis methods was conducted to systematically investigate their structures, mesophase behaviors and optical properties. The length and parity of the flexible spacers has a dramatic influence on the mesomorphic behaviors, and an odd-even effect is observed for these chiral liquid crystal compounds.

Engineering the Thermodynamic Stability and Metastability of Mesophases of Colloidal Bipyramids through Shape Entropy.

We report several types of entropy-driven phase transition behaviors in hard bipyramid systems using Monte Carlo simulations. Bipyramidal nanoparticle shapes are synthesizable from gold and silver, with sizes ranging from tens to hundreds of nanometers. We report numerous colloidal crystalline phases with varying symmetries and complexities as the bipyramid aspect ratio and base polygon are varied. Some bipyramids are mesogenic and undergo either monotropic or enantiotropic phase transitions. We show that such mesophase behavior can be modulated by tuning the bipyramid aspect ratio. In addition, we report stepwise kinetic crystallization and melting pathways that occur via an intermediate mesophase as the system gains or loses order in successive stages. Our results demonstrate that complex phase transition behavior involving mesophases can be driven by entropy alone. Importantly, our results can guide the synthesis of bipyramid shapes able to assemble target structures and can be used to engineer the kinetic pathways to and from those structures to involve or avoid mesophases.

Generation of mono-mesophase in allylidene-based homologues with a longer molecular axis

In this article, we have synthesized twenty-eight nematogenic homologous derivatives of allylidene base with cinnamates and benzoates linkages. All nematogenic homologous derivatives were characterized by ultraviolet spectroscopy, Infrared and proton magnetic resonance with study of their mesophase properties by the polarized optical microscope (POM) where they were found to be enantiotropically nematogenic. The thermograms of mesophase transition enthalpies and entropies were recorded by differential scanning calorimetry (DSC). The geometries of all molecules were optimized by DFT/B3LYP method using a basis set def2-SVP, the result of these calculated molecule's geometries for all molecules showed to have an electron-rich longer molecular axis, which enables the molecule to form a stronger pi interaction with adjacent molecules and induces the nematogenic mesophase behavior. The effect of an additional diene system on mesophase behavior of a stepped type of molecules was also studied. The role of the number of rings on mesophase behavior as an odd-even effect on mesophase transition temperature as well as the role of the substitution on the terminal ring for the same was considered.

Lipid doping of the sponge (L3) mesophase.

The polymorphism of lipid aggregates has long attracted detailed study due to the myriad factors that determine the final mesophase observed. This study is driven by the need to understand mesophase behaviour for a number of applications, such as drug delivery and membrane protein crystallography. In the case of the latter, the role of the so-called 'sponge' (L3) mesophase has been often noted, but not extensively studied by itself. The L3 mesophase can be formed in monoolein/water systems on the addition of butanediol to water, which partitions the headgroup region of the membrane, and decreases its elastic moduli. Like cubic mesophases, it is bicontinuous, but unlike them, has no long-range translational symmetry. In our present study, we show that the formation of the L3 phase can delicately depend on the addition of dopant lipids to the mesophase. While electrostatically neutral molecules similar in shape to monoolein (DOPE, cholesterol) have little effect on the general mesophase behaviour, others (DOPC, DDM) significantly reduce the composition at which it can form. Additionally, we show that by combining cholesterol with the anionic lipid DOPG, it is possible to form the largest stable L3 mesophases observed to date, with characteristic lengths over 220 Å.