Mesophase Stability Research Articles

Three-Dimensional Imaging of Bioinspired Lipidic Mesophases Using Multicolored Light-Emitting Carbon Nanodots.

Recent progress in the design of carbon nanostructures exhibiting strong multiphoton-excited emission opens new pathways to explore the self-organization of lipids found in living organisms. Phospholipid-based lyotropic myelin figures (MFs) are promising materials as simplified models of biomembranes due to their structural resemblance to a multilamellar sheath insulating the axon. This study demonstrates the possibility of selective labeling of MFs by strongly emitting multicolor phloroglucinol-derived carbon nanodots (PG CNDs). Such dopants are efficiently excited by visible and near-infrared light; therefore, one- and two-photon fluorescence microscopies are incorporated to gain 3D insights into the MFs. Combining nondestructive fluorescence microscopy and spectroscopy techniques along with polarized light microscopy gives details on the stability and morphology of lipidic mesophases. Our findings suggest that PG CNDs can be a viable and simple alternative to conventional fluorescent lipid stains to image biologically relevant phospholipid-based structures.

Coumarin Schiff base derivatives with terminal cyano group: Synthesis, Mesomorphic properties and DFT investigation

Coumarin Schiff base derivatives with terminal cyano group were synthesized and analysed for their mesomorphic behaviour. The homologous series CN6–16 (n = 6,8,10,12,14,14,16) with 4-cyano benzaldehyde, lower member (n = 6,8) exhibited enantiotropic nematic mesophase, while smectic A mesophase started appearing with n = 8 during cooling process. Enantiotropic smectic A mesophase was observed with higher chain length n = 10,12,14,16. Similar trend of mesomorphic properties was exhibited by Schiff base derivatives BPCN8–14. Introduction of cyano biphenyl at aldehyde end of the molecule has led to formation of stable smectic A mesophase as compared to that by compounds CN8–14. Introduction of ester linkage in Schiff based derivatives, compounds ECN10–12 and RECN10–12 showed smectic A mesophase with high clearing temperature. VT-XRD analysis of two compounds has confirmed orthogonal smectic A mesophase. Additionally, DFT calculations were carried out for all the newly synthesized compounds and compared with similar literature molecules for various structural and electronic parameters followed by their correlation with the mesophase type and stability.

Self‐Assembled Cyclotriguaiacyclene‐Integrated Supramolecular Systems for Liquid Crystal and Self‐Assembly Behavior

AbstractAn advanced tri‐substituted supramolecular material was synthesized via conversion of cyclotriveratrylene to cyclotriguaiacyclene with further esterification reaction with fluorescein unit embedded with side‐arms. All four luminescent materials exhibited columnar hexagonal type mesophase on both heating and cooling conditions. The materials with hexadecyloxy and octadecyloxy tail group exhibit liquid crystalline behavior at room temperature indicating the presence of a mesophase even under ambient conditions. By combining polarizing optical microscopy, differential scanning calorimetry, and high‐temperature X‐Ray diffraction techniques to understanding the optical, thermal, and molecular packing behavior of the compounds in the liquid crystalline state. The cyclotriguaiacyclene core with high fluorescent nature displayed columnar hexagonal type self‐assembly at room temperature. All four supramolecular mesogens showed higher thermal stability of mesophase. The computational study provides the importance of the electronic nature of the compounds.

Coumarin Schiff base derivatives with 4′-alkoxy biphenyl-4-carboxaldehyde: Synthesis, mesomorphic studies and DFT calculations

Two homologous series of coumarin Schiff base derivatives with 4′-alkoxy biphenyl-4-carboxaldehyde have been designed and synthesized. All the compounds were analyzed IR, 1H NMR, 13C NMR, ESI-MS and CHN analysis followed by mesomorphic properties polarizing optical microscopy (POM) and differential scanning calorimetry (DSC) analysis. In the first homologous series BPS(6–16), Schiff base of 7-alkoxy-3-aminocoumarin with 4′-alkoxy biphenyl-4-carboxaldehyde, alkoxy chain length was varied systematically at both end of the molecules such as n = 6,8,10,12,14,16. In this series, BPS(6–10) (n = 6,8,10) exhibited enantiotropic nematic(N) and smectic C (SmC) mesophase and turned to monophasic on increasing the chain length n = 12,14,16 in BPS(12–16) with stable SmC mesophase. While in the second homologous series 10BPU(2–16), systemic variation of alkoxy chain length was carried out at coumarin end only (n = 2–18) and 4′-decyloxy-biphenyl-4-carboxaldehyde was used for Schiff base formation. In the this series, early member of the series with n = 2,3 showed enantiotropic very stable (∼ 145 °C) nematic mesophase, while N as well as SmC mesophase were observed for n = 4–8 at, whereas with increase of chain length stability of nematic mesophase was decreased and that of SmC was increased. Higher membered analogous 10BPU(12–16) exhibited SmC mesophase with stability in the rage of 130–160 °C. VT-XRD analysis was also confirmed the tilted SmC mesophase in this class of compounds. For both the series, all compounds were studied for the DFT calculations as well as literature molecules with similar variations. Based on the calculated structural (length, aspect ratio) and electronic (dipole moment, polarizability) parameters were correlated with mesomorphic behaviour observed for literature compounds and compounds from both the series followed by the detailed discussion.

Asymmetric naphthalene centred bis-ester Schiff base: Self-assembling behaviour and DFT approach

New asymmetric 2,6-disubstituted naphthalene embedded Schiff base-bis esters NEKE-(2–18) synthesized and investigated for their mesomorphic behaviour. One end of naphthalene has been substituted by decyloxy long chain whereas the other end connected with imine-bis ester aromatic core with terminal long chains. New molecules have been found to exhibit polymorphic behaviour with good thermal stability and enhanced mesophase stability upon POM (polarising optical microscopy) and DSC (differential scaling calorimetry) investigations. Early members (C2 and C3) showed nematogenic behaviour along with SmA (smectic-A) mesophase, whereas molecules with C4 and C5 showed only SmA phase. Compounds with C6 and C7 showed monotropic SmC (smectic-C) upon cooling whereas molecules from C8-to-C18 exhibited enantiotropic SmC along with SmA mesophase. The presence of mesophase has been confirmed by VT-XRD (variable temperature X-ray-crystallography) analysis. For comparison and better understanding, the mesomorphic data of compounds from literature has been compared. The DFT (density functional theory) calculations were performed on both new compounds and structurally analogous molecules found in literature. A detailed discussion was carried out regarding the correlation between the mesomorphic behaviour observed in new compounds and literature, and the computed structural (length, aspect ratio) and electronic (dipole moment, polarizability) variables.

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.

The interplay of chirality and restricted rotation: stabilisation of chiral, frustrated mesophases over a wide thermal range.

Introducing restricted rotation in a molecule, often achieved through the incorporation of double or triple bonds, constitutes a crucial approach to induce a frustrated mesophase. Furthermore, the inclusion of a chiral moiety, such as cholesterol, serves to enhance the stabilization of chiral frustrated mesophases. This study presents the synthesis and characterization of novel optically active dimers incorporating cholesterol and phenyl 3-phenylpropiolate segments interconnected by an ω-oxyalkanoyloxy spacer with varying lengths and parity. Comprehensive characterization using POM, DSC, and X-ray diffraction techniques reveals that these mesogens exhibit enantiotropic liquid crystal (LC) phases. Due to the restricted rotation caused by the triple bonded system, these dimers stabilized the frustrated chiral mesophase TGBC* over a wide temperature range. The identified phases include BP-I/II, N*, and SmA, with odd-membered dimers commonly displaying N* and SmA phases and one member additionally exhibiting BP-I/II. Even-membered dimers exhibit N* and TGBC* phases, with the latter spanning an impressive thermal range of 37 °C to 84 °C. Notably, the thermal range of the TGBC* phase widens with an increase in the terminal tail length. Across the series, clearing temperatures generally decrease with the elongation of the terminal tail, and even-membered dimers consistently exhibit higher clearing temperatures than their odd-membered counterparts, illustrating the spacer's parity-dependent odd-even effect on the dimers' phase transition behavior.

Induction and Stabilization of Columnar Mesophases in Fluorinated Polycyclic Aromatic Hydrocarbons by Arene-Perfluoroarene Interactions.

The straightforward synthesis of several Fluorinated Polycyclic Aromatic Hydrocarbons by the efficient, transition-metal-free, arene fluorine nucleophilic substitution reaction is described, and the full investigation of their liquid crystalline and optical properties reported. The key precursors for this study, i. e. 2,2'-dilithio-4,4',5,5'-tetraalkoxy-1,1'-biphenyl derivatives, were obtained in two steps from the highly selective Scholl oxidative homo-coupling of 3,4-dialkoxy-1-bromobenzene, followed by quantitative double-lithiation. In situ room temperature nucleophilic annulation with either perfluorobenzene or perfluoronaphthalene leads to 1,2,3,4-tetrafluoro-6,7,10,11-tetraalkxoytriphenylenes and 9,10,11,12,13,14-hexafluoro-2,3,6,7-tetraalkoxybenzo[f]tetraphenes, respectively, in good yields. Exploiting the same strategy, subsequent double annulations resulted in the formation of 9,18-difluoro-2,3,6,7,11,12,15,16-octa(alkoxy)tribenzo[f,k,m]tetraphenes and 9,10,19,20-tetrafluoro-2,3,6,7,12,13,16,17-octakis(hexyloxy)tetrabenzo[a,c,j,l]tetracenes, respectively. Despite the presence of only four alkoxy chains, the polar "Janus" mesogens display a columnar hexagonal mesophase over broad temperature ranges, with higher mesophase stability than the archetypical 2,3,6,7,10,11-hexa(alkoxy)triphenylenes and their hydrogenated counterparts. The improvement or induction of mesomorphism is attributed to efficient antiparallel face-to-face π-stacking driven by the establishment of non-covalent perfluoroarene-arene intermolecular interactions. The larger lipophilic discotic π-extended compounds also exhibit columnar mesomorphism, over similar temperature ranges and stability than their hydrogenated homologs. Finally, these fluorinated molecules form stringy gels in various solvents, and show interesting solvatochromic emission properties in solution as well as strong emission in thin films and gels.

Influence of monohalogenated flexible tails on the mesomorphism of triphenylene-based discotics

A series of triphenylene-based discotic liquid crystals (DLCs) modified by fluorination or chlorination at the end of peripheral flexible chains were examined in this work. DLC derivatives containing one mono fluorine or chlorine-substituted flexible chain 4a-e and six mono fluorine or chlorine-substituted flexible chains 8a & 8b, 10a & 10b were mainly synthesized and molecular structures confirmed by 1H NMR, 19F NMR and MALDI-TOF MS. The mesogenic properties of the obtained compounds were further studied by differential scanning calorimetry (DSC), polarizing optical microscopy (POM) and X-ray diffraction (XRD). Impressively, compounds 4a-e were found exhibiting hexagonal columnar phases and the π-π stacking distances of 4a-e were lower than that of the parent molecule HAT5. Due to the influence of atomic radius and molecular symmetry, the mesophase stability of the fluorinated triphenylene compounds was greater than the chlorinated ones. Through the modification of the side chain, the self-assembly behavior of triphenylene was stronger and the intracolumnar distance was decreased, which may give rise to a higher charge transport mobility. Compound 10b showed self-assembly behavior and formed a spherulite texture that could also remain orderly until room temperature. This is rare in reported DLCs and it might be applied as active components of in electronic devices. These ordered stacked discotic molecules may exhibit improved charge carrier mobility as semiconducting materials.

Synthesis, characterization and structure-mesomorphic properties relationship of palm-based azo-ester bridged liquid crystals from caprylic acid

This paper discussed the liquid crystal properties of a new homologous series derived from palm caprylic acid that differ in terms of terminal substituents. The chemical structures of synthesized compounds were characterized by nuclear magnetic resonance (NMR), fourier transform infrared (FT-IR) and CHN elemental analysis, while the mesomorphic behaviors were evaluated by polarized optical microscopy (POM) and differential scanning calorimetry (DSC). The insertion of a polar substituent i.e. -CH3 (BME), -OCH3 (BMO), -OCH2CH3 (BEO) at the sixth position on the benzothiazole ring was able to reveal broad nematogenic temperature ranges (65.60–141.48 °C). The nematic mesophase stability is in order of BEO > BMO > BME, with two of them revealing their mesophase characteristics at nearly room temperature. This finding endorses a strong association between polarity factor and mesomorphism which was confirmed through density function theory with the basis set of 6–311 G d,p. The molecules also exhibit relatively high thermal stability (218–312 °C). This finding might be helpful in future structure design of palm-based LCs, as well as encourage the efforts in utilizing palm oil as a renewable and cheaper resource alternative, particularly in non-edible areas such as oleochemical-related research and development.

Effect of molecular aspect ratio on structure, dynamics and phase stability of thermotropic liquid crystals studied by molecular dynamics simulation

Due to the importance of liquid crystals in modern technology and food industry, understanding their structural and dynamical properties are scientifically important. In this study, we applied extensive molecular dynamics simulations to infer the effect of the molecular elongation on the formation, stability and dynamics of liquid crystal mesophases in a system of Gay-Berne model mesogens with parameters GB (k,k′=20,μ=1,ν=1). Four aspect ratio values, k=2,3,4.4 and 5, were studied at pressure P*=4. Thermodynamics properties, the order parameter and pair distribution functions (both translational and positional), helped to identify phases, hysteresis, and consequently phase diagrams. By increasing aspect ratio from 2 to 5, nematic and smectic phases were induced and all transition temperatures were shifted to higher values, hence, the range of stability of the nematic and smectic mesophases became wider. The analysis of the coordination numbers and angular distribution functions showed that the structure of the solid phase of system with k=2 at lowest temperatures was fcc which by increasing the aspect ratio changed to a complete hexagonal in-layer structure. Moreover, by increasing the axial ratio of particles, decoupling between the principal components of diffusion coefficients increased, where it reflects an increase in the molecular orientational order in the system with higher k. The effect of increasing aspect ratio was more pronounced on inter-layers diffusion rather than the in-layers. In all mesophases parallel components of diffusion coefficients were greater than the perpendicular components. We analyzed the results based on the existing theoretical descriptions and experimental observations.

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.

Liquid crystalline electrolytes derived from the 1,12-disubstituted [closo-CB11H12]– anion

A new approach to anisotropic liquid electrolytes is explored. Thus, a non-ionic liquid crystalline host exhibiting SmC and N phases is doped with a lithium salt containing an anion structurally similar to the host and derived from the weakly-nucleophilic [closo-CB11H12]– cluster. The resulting unaligned 5, 10, and 15 mol% solutions of the lithium salt in the host were investigated by optical, thermal, powder XRD and impedance spectroscopy methods in a broad temperature range. The results showed that the increasing concentration of the ionic additives essentially does not affect the mesophase stability, but expands the lamellar SmA phase possessing ion conducting channels. At the same time ionic conductivity, σ, monotonically increases from 10-8 to 10-4 S cm−1 with increasing temperature (20–120 °C) and with increasing Li+ ion concentration. The Arrhenius analysis of the conductivity data revealed progressively decreasing activation energy EaIC from crystalline (∼102 kJ mol−1), to SmA (∼70 kJ mol−1) and to nematic (∼30 kJ mol−1) phases. The electrochemical stability window of the 15 mol% electrolyte was determined as 1.3–4.6 V vs Li metal anode.

Design of Liquid Crystal Materials Based on Palmitate, Oleate, and Linoleate Derivatives for Optoelectronic Applications

Herein, liquid crystalline derivatives based on palmitate, oleate, and linoleate moieties with azomethine cores were synthesized, and their physical, chemical, optical, and photophysical properties were investigated in detail. The mesomorphic activity of these materials was examined through polarized optical microscopy (POM) and differential scanning calorimetry (DSC). The observed results revealed that the stability of the thermal mesophase depends on the terminal polar as well as on the fatty long-chain substituents. Purely smectogenic phases were detected in all three terminal side chains. A eutectic composition with a low melting temperature and a broad smectic A range was found by constructing a binary phase diagram and addressing it in terms of the mesomorphic temperature range. The energy bandgap of the palmitate-based derivative (Ia) was determined as 3.95 eV and slightly increased to 4.01 eV and 4.05 eV for the oleate (Ib) and linoleate (Ic) derivatives, respectively. The optical constants (n, κ, εr, and εi) were extracted from the fitting of measured spectroscopic ellipsometer data. The steady-state spectra of these samples exhibited a broad emission in the range 400-580 nm, which was found to be blue shifted to 462 nm for both Ib and Ic derivatives. The average fluorescence decay lifetime of the Ia derivative was found to be 598 ps, which became faster for the Ib and Ic derivatives and slower for the sample with a chloride end polar group.

Identifying pathways to metal-organic framework collapse during solvent activation with molecular simulations.

Metal-organic framework (MOF) materials are a vast family of nanoporous solids with potential applications ranging from drug delivery to environmental remediation. Application of MOFs in these scenarios is hindered, however, by difficulties in MOF 'activation' after initial synthesis - removal of the synthesis solvent from the pores to make the pore space accessible - often leading to framework collapse if improperly performed. While experimental studies have correlated collapse to specific solvent properties and conditions, the mechanism of activation-collapse is currently unknown. Developing this understanding would enable researchers to create better activation protocols for MOFs, accelerating discovery and process intensification. To achieve this goal, we simulated solvent removal using grand-canonical Monte Carlo and free energy perturbation methods. By framing activation as a fluid desorption problem, we investigated activation processes in the isoreticular metal organic framework (IRMOF) family of MOFs for different solvents. We identified two pathways for solvent activation - the solvent either desorbs uniformly from each individual pore or forms coexisting phases during desorption. These mesophases in turn lead to large capillary stresses within the framework, corroborating experimental hypotheses for the cause of activation-collapse. Finally, we found that the activation energy of solvent removal increased with pore size and connectivity due to the increased stability of solvent mesophases, matching experimental findings. Using these simulations, it is possible to screen MOF activation procedures, enabling rapid identification of ideal solvents and conditions and thus enabling faster development of MOFs for practical applications.

Electronic and structure conformational analysis (HOMO-LUMO, MEP, NBO, ELF, LOL, AIM) of hydrogen bond binary liquid crystal mixture: DFT/TD-DFT approach

Novel hydrogen bond liquid crystal (HBLC) binary mixture is designed and optimized through density functional theory (DFT) calculation and time dependent density functional theory (TD-DFT). HBLC binary mixture is derived from mesogenic compounds of liquid crystalline 4-methoxycinnamic acid (4MCA) and 4-hexyloxybenzoic acid (6OBA). Theoretically predicted vibrational IR assignments HBLC binary mixture is compared with experimental FTIR and validated. TD-DFT calculation is used to identify electronic absorption spectrum of HBLC binary mixture. Molecular electrostatic potential analysis explores the electrophilic/nucleophilic charge distribution and chemical reactivity of binary mixture, whereas natural bond orbital (NBO) study discloses the possible intermolecular hyper-conjugative interaction. HOMO and LUMO study shows charge transfer phenomena between 4MCA and 6OBA compounds. Further, Topological studies confirm the strong hydrogen bond between 4MCA and 6OBA. It is identified as the π- π stacking of the aromatic part of carboxylic acid plays an important role in the improved phase stability of mesophases.

Synthesis, Characterization, and Investigation of Mesomorphic Properties of a New 2,5-Bis-(4-alkanoyloxybenzylidene)cyclopentan-1-one.

A new set of cyclopentanone chalcone esters2,5-bis-(4-alkanoyloxybenzylidene)cyclopentan-1-one (B2-B10) has been synthesized and monitored by TLC. Structures of these compounds were determined by spectroscopic techniques (FTIR, H NMR, and mass spectrometry). Differential scanning calorimetry (DSC) and polarized optical microscopy were used to evaluate their transition temperatures and mesophase properties (POM) throughout heating and cooling scans. The thermal data indicate that the compounds B5-B10 have mesomorphic properties with thermal stabilities; the data also reveal that the compounds B6-B10 are monotropic, whereas B5 is enantiotropic. B6, B7, and B9 only have a nematic phase, but B8 and B10 have a smectic phase followed by a nematic phase, and B5 only has a smectic phase. In addition, the study reveals that the inclusion of an acyl group as a terminal chain had the opposite effect on isotropization temperatures for compounds B6, B8, and B10, resulting in an increase in transition temperatures and a decrease in mesophase stability. The lack of a smectic phase in B7 and B9 compounds could be attributed to the narrow phase temperature range, which makes examination difficult, or to the molecules' lack of lateral attraction.

Hydrogen-bonding stabilized columnar mesophases in hexasubstituted triphenylene 2,3-Dicarboxamides

A series of new mixed tail triphenylene derivatives having four β-alkoxy and two adjacent β-carboxamide side chains have been prepared and characterized. The synthesis was carried out by amidation of the triphenylene 2,3-dicarboxylic methyl ester with various primary amine. All the dicarboxamides exhibit an enantiotropic Colh phase, except compound TPC6-(CONHC6H13)2 bearing the shortest hexyloxy chains. Effects of variation in lengths of alkoxy and N-alkyl chains on mesogens were also studied and the pronounced influence of lengths of alkoxy chains turned out to be more important than that of N-alkyl chains. Furthermore, the intermolecular hydrogen bonding induced by amide functions in TPC8-(CONHC4H9)2 does indeed enhance the mesophase stability in comparison to the non-hydrogen bonding ester TPC8-(COOC4H9)2, as reflected by higher clearing temperatures and evidenced by temperature-dependent FT-IR studies. Although the compound TPC6-(CONHC6H13)2 was found to decompose to imide compound on the hot stage before clearing in the course of the POM experiment, only it shows good gelation property in single toluene, indicating that the intermolecular hydrogen bonding is not the only factor responsible for the formation of gel in these molecules.

Evidence of Counterion Size Effect on the Stability of Columnar Phase of Ionic Liquid Crystals Based on Pyridinium Salts Derived from N-3,4,5-Tri(alkyloxy)-benzyl-4-pyridones

The synthesis and characterization of novel ionic liquid crystals based on pyridinium salts with Br− and PF6− counterions are described in this work. These pyridinium salts were derived from 4-hydroxypyridine, both by N- and O-alkylation. The 3,4,5-tri(alkyloxy)-benzyl mesogenic unit was attached to the nitrogen atom of the pyridinium ring. Alkyl chains with a different number of carbon atoms (6, 8, 10, 12 and 14) were employed in order to show the effect on the stability of mesophase. The POM (polarizing optical microscopy) and XRD (powder X-ray diffraction) studies indicated that bromide salts with shorter chains C6, C8 and C10 do not show mesomorphic properties, while longer chain analogues with C12 and C14 exhibit two enantiotropic columnar phases. Surprisingly, the pyridinium salts with the larger size PF6− counterion do not exhibit liquid crystal properties.

New (-)-menthol-based blue phase liquid crystals with different polar substituents in the terminal group: Synthesis, mesophase behaviors, and DFT calculations

Eight novel Schiff base ester chiral liquid crystals, MtLC-X (X: -OCH3, -CH3, -F, -H, -CF3, -OCF3, -NO2, -CN), were successfully synthesized and analyzed for their mesophase formation and stability. Each of them was attached to the end of (-)-menthol as a chiral group, and the other end of these molecules was connected with different polar substituent X. The chemical structures of the prepared compounds were characterized via FT-IR, 1H NMR and 13C NMR. The combination differential scanning calorimeter (DSC), polarizing optical microscopy (POM) and X-ray diffraction (XRD) measurements were carried out to systematically study the characterization of mesomorphic properties. The photophysical property was studied by UV–vis spectroscopy. All the prepared CLCs, besides the H derivative, MtLCH, are mesomorphic exhibiting N* and/or SA* mesophase. The results revealed that the mesomorphic behavior and the clearing point of mesophase (Tc) correlate well with polarizability anisotropy (Δα).