Enantiotropic SmA Phase Research Articles

A “core determination” phenomenon in four dichiral liquid crystals containing two lactate groups

Four dichiral liquid crystals with one perfluoroalkyl chain and two lactate groups were synthesized. They all exhibit an enantiotropic SmA phase. An enantiotropic SmCd* phase was identified in a pair of enantiomers. Their optical activity was mainly controlled by the chirality of the lactate residue near mesogenic core. These liquid crystals could self-assemble into twisted nanoribbons or helical nanofibers. The stacking handedness of mesogenic cores and the handedness of nanoribbons/nanofibers were also dominated by the chirality of lactate group near mesogenic core. This “core determination” phenomenon was proposed to originate from the π–π stacking among mesogenic cores.

Mesomorphic behaviors of some acrylate liquid crystals and their application for polarizer preparation

ABSTRACT Two series of acrylate liquid crystals with enantiotropic SmA and SmC phases were synthesised. With increasing the alkoxy chain length, SmC phase was favourable to be formed. The mesophases were confirmed by taking small angle X-ray scattering patterns. Moreover, a diacrylate liquid crystal with an enantiotropic SmA phase was synthesised. Smectic liquid crystal mixtures were prepared using the diacrylate liquid crystal (or a mixture of an acrylate liquid crystal and the diacrylate one) and a dichroic dye. After photopolymerisation at the SmA phase, polymeric polarisers were obtained. The degree of polarisation was increased with increasing the dye concentration and film thickness.

Lateral fluoro-substitution driven molecular packing difference in a series of pyridinium-based chiral ionic liquid crystals

ABSTRACT A series of pyridinium-based chiral ionic liquid crystals (ILCs) and the intermediated, non-ionic ones (NILCs), were designed and synthesised. All ILCs exhibit enantiotropic SmA phases, while all NILCs exhibit enantiotropic cholesteric and SmA phases. In addition, few of NILCs and ILCs exhibit enantiotropic SmC* phases. Due to the Coulombic force, the clearing points of the ILCs are higher than those of the corresponding NILCs. For ILCs, the lateral fluoro-substitution not only decreases the clearing points, but also drives the formation of bilayer molecular packing structures at the smectic phases.

Molecular packing handedness dominated by the chirality of the lactic acid residue near the liquid crystalline core

ABSTRACT Eight dichiral compounds containing two lactic acid residues and one perfluorocarbon chain are synthesised. Six of them are liquid crystals with an enantiotropic SmA phase. Two of them are liquid crystals with enantiotropic SmA and SmC* phases. Although (R,R)-3 and (R,R)-4 molecules pack in monolayer structures at the crystalline states, (S,R)-3 and (R,S)-4 molecules pack in bilayer structures at the crystalline states. The optical activity of these compounds is mainly controlled by the chirality of the lactic acid residue near the liquid crystalline core. The dichiral compounds can self-assemble into nanotubes or twisted nanoribbons in methanol. Circular dichroism characterisation indicated that the stacking handedness of the liquid crystalline cores in the organic self-assemblies was also dominated by the chirality of the lactic acid residue near the liquid crystalline core.

Synthesis, mesomorphic and dielectric properties of new bent-core liquid crystal with a terminal lactate group

The synthesis, liquid crystalline properties and dielectric properties of a new bent-core compound (DBOB) composed of terephthalate based rod-like units with a O-dodecyl lactate group substituted at one side as well as n-octyloxy located at other terminal are presented. The liquid crystalline properties have been investigated by polarizing optical microscopy, differential scanning calorimetry and electro-optical studies. The dielectric parameters and phase regions of DBOB, which exhibits an enantiotropic non-polar SmA phase between 156 and 100 °C as well as SmA phase with a ferroelectric polar response at lower temperatures than 100 °C, have been carried out by impedance spectroscopy at different temperatures. The dielectric relaxation mechanisms have been analyzed by Cole-Cole plots. The Debye distribution parameters and activation energies have also been determined.

Synthesis and characterization of new bent-core liquid crystal with a ferroelectric-like switching / modified magnetite nanocomposite

A new bent-core liquid crystal (LC) compound 4-Cyano-1,3-phenylenebis[4-(4-(S)-2-Dodecyloxypropionyloxyphenoxycarbonyl)benzoate] (CyPDB) consisting of O-dodecyl lactate substituted terephthalate based rod-like units which were located at 1,3-positions of 4-cyanoresorcinol central unit has been synthesized and LC/1.0% modified Fe3O4 nanocomposite has been prepared. The effects of being the doped with 1.0% modified Fe3O4 (magnetite) nanoparticles on mesomorphic properties of the new bent-core liquid crystal, which exhibits an enantiotropic SmA phase with a ferroelectric-like switching, were investigated by differential scanning calorimetry, optical polarizing microscopy and electro-optic studies. The surface of Fe3O4 (magnetite) nanoparticles was modified with a silane surfactant, octadecyltrimethoxysilane (OTMS), used as a compatibilizer for the attractive interaction of liquid crystal molecule with Fe3O4 nanoparticles. The size, morphology and distribution of modified Fe3O4 (magnetite) nanoparticles in LC host were investigated by using Transmission Electron Microscope (TEM) and Scanning Electron Microscopy (SEM). The magnetic properties of nanocomposite were studied using a vibrating-Sample Magnetometer (VSM).

Dielectric properties of liquid crystals from the thioester series with a terminal polar group

ABSTRACTThis paper presents the results of our studies of the phase transition behaviour and dielectric properties of three compounds from two series of thiobenzoates characterised by the presence of polar terminal groups. In two of the compounds (5OSCl and 6OSCl), the polar terminal substituent is −Cl, whereas the third compound (11OSNO2) has a terminal nitro group. The compound 5OSCl has an enantiotropic nematic phase N and monotropic smectic A phase and 6OSCl is characterised by the existence of two enantiotropic phases, the N and smectic A phases. The compound 11OSNO2 only exhibits an enantiotropic SmA phase. The permanent dipole moments of the studied molecules are located parallel to their long axes, which promotes the formation of SmA phase variants. The results of dielectric permittivity dispersion and absorption and spontaneous polarisation measurements allowed the SmA phase to be identified in the compounds we investigated.

Chirality driven mesomorphic behaviour difference: dichiral compounds containing two lactate groups

ABSTRACTFour compounds containing two lactate groups and one perfluorocarbon chain are designed and synthesised, whose chirality is tuned by changing the chirality of the lactic acid residues. (R,S)- and (S,R)-2 stereoiosomers exhibit an enantiotropic SmA phase, while (R,R)- and (S,S)-2 stereoisomers exhibit an enantiotropic SmA phase and an enantiotropic SmCd* one. Therefore, the chirality of the compounds plays an important role in the mesomorphic behaviours of the compounds. The optical activity of these liquid crystals is dominated by the chirality of the lactate group near the core. (R)- and (S)-1 with one lactic acid residue and one perfluorocarbon chain exhibit only an enantiotropic SmA phase.

Liquid crystalline behaviours of some 3-perfluoroalkylbenzoate esters

ABSTRACTA series of 3-perfluoroalkylbenzoate esters are synthesised. They tend to exhibit enantiotropic SmA and SmC phases. The clearing points are decreased with increasing the alkoxy chain length and show odd-even effect. With increasing the fluorocarbon chain length, the melting and clearing points increase; however, the SmC phase is suppressed.

Terminal Effect of the Semi-fluorocarbon Chain on the Liquid Crystalline Behaviors of Some Compounds

Two series of chiral compounds with semi-perfluorocarbon chains and alkoxy ones, nBP4F and nBP6F, are synthesized. Enantiotropic SmA phase is identified in all of these compounds. When the alkoxy chain length is short, enantiotropic SmB is also identified. When the alkoxy chain length is longer than 6 carbons, enantiotropic SmC* phase is formed. Their clearing points increase with increasing the perfluorocarbon chain length. Comparison of compounds with -CF3, -CHF2 and -CF2Cl groups at the terminals of the fluorocarbon chains, the clearing point sequence is -CHF2 < -CF2Cl < -CF3; and the melting point sequence is -CF3 < -CHF2 < -CF2Cl. Therefore, the compounds with semi-perfluorocarbon chains show the widest liquid crystalline temperature range. Moreover, the SmC* phase of the compounds with -CF3 at the terminals shows the highest thermostability.

Asymmetric 1,3,4-thiadiazole derivatives: Synthesis, characterization and studying their liquid crystalline properties

Non-symmetrically series of eleven compounds derived from 2,5-disubstituted central 1,3,4-thiadiazole derivatives, n-alkyl-4-(5-(4-methoxyphenyl)-1,3,4-thiadiazol-2-yl)benzoate, n = 1–10, 12 (B1-B11) were synthesized. These homologues were characterized by FTIR, 1HNMR, 13CNMR and most of them by mass spectrometry. The mesophase textures and thermal behaviors were investigated by polarizing optical microscopy (POM) and differential scanning calorimetry (DSC), respectively. Thermodynamic parameters, ΔH and ΔS, of the transitions were calculated from (DSC) thermograms. The derivatives with short ester arm (B1-B7) displayed enantiotropic liquid crystal behaviors with SmA and N phases on heating and cooling cycles, whilst the last four analogues with the longest ester arm (B8-B11) exhibiting enantiotropic SmA phase on heating and SmA, SmE phases on cooling. The effects of the heterocyclic core and the number of carbon atoms in ester chain on the mesomorphic behaviors of these compounds were discussed. Also, these results were compared to other compounds that have similar confirmations.

Novel bent-core mesogenic of 4-amino-triazole derivatives: synthesis, characterization and liquid crystalline study

The synthesis, characterization and mesomorphism of twelve new bent-shaped mesogens containing 4-amino-1,2,4-triazole as a central rigid core (II)n are reported. The amino triazole derivatives were characterized by 1H, 13C NMR spectroscopy, FT infrared, elemental analysis and one of them by mass spectrometry. The mesophase behavior was investigated using polarizing optical microscopy (POM) and differential scanning calorimetry (DSC). The homologues with short alkoxy terminal groups (II)a–d do not show any mesomorphic properties and only crystal to isotropic transition was observed by POM, whilst the analogue with the longest alkoxy terminal groups (II)e–l exhibit enantiotropic SmA, B1, B2, B6 and B7 phases with wide mesomorphic temperature ranges. The effect of the triazole ring and the length of the terminal alkoxy chains on the liquid crystals behavior of the compounds were discussed.

Effect of lateral substituent and chain length on mesomorphic properties of novel alkoxy benzyloxy benzoates of cyanophenyl rod-shaped compounds

Three novel homologous series of rod-shaped cyanophenyl alkoxy benzoate liquid crystalline compounds with lateral polar fluorine and chlorine substituent were prepared, and chemical structures of novel materials have been characterized by standard spectral technique and elemental analysis. The mesophase characterization was carried out using the combination of polarized optical microscopy and differential scanning calorimetry. All the compounds exhibit wide thermal range of enantiotropic SmA phase.

Calamitic liquid crystals of 1,2,3-triazole connected to azobenzene: synthesis, characterisation and anisotropic properties

Azobenzene-based calamitic liquid crystals, 4-((4-(4-methoxymethyl-1,2,3-triazol-1-yl)phenyl)diazenyl)phenylalkanoates have been isolated and their structures were characterised. The structure–property correlation with respect to the different alkanoyloxy terminal chain (–COOCnH2n+1 where n adopts odd numbers ranging from 3 to 15) has also been given attention in the present study. In this series, all compounds exhibit smectogenic properties. The lower homologues shows enantiotropic SmA phase as well as monotropic SmC phase. The higher homologues exhibit homeotropic alignment of smectic phases. These compounds possess very high anisotropic inclination in which the mesomorphic region covers nearly 80°C.

4-[4-(Heptyloxy)benzoyloxy]phenyl 2-oxo-7-trifluoromethyl-2H-chromene-3-carboxylate

The title compound, C31H27F3O7, is a liquid crystal and exhibits enanti­otropic SmA and nematic phase transitions. In the crystal, the the 2H-chromene ring system makes dihedral angles of 54.46 (17) and 7.79 (16)°, respectively, with the central benzene ring and 4-(hept­yloxy)benzene ring. The three F atoms of the –CF3 group are disordered over two sets of sites, with an occupancy ratio of 0.62 (3):0.38 (3). The crystal structre features two pairs of C—H⋯O hydrogen bonds, which form inversion dimers and generate R 2 2(10) and R 2 2(30) ring patterns. C—H⋯O inter­actions along [100] and C—H⋯π inter­actions futher consolidate the packing, leading to a three-dimensional network.

Mesomorphism Behavior of Two Series of Chiral Compounds with Semiperfluorocarbon Chains

Thermotropic liquid crystals with fluorocarbon chains have attracted much attention, because they are feasible to form smectic phases. Herein, two series of chiral compounds with semiperfluorocarbon chains were designed and synthesized. These compounds were characterized by IR, 1H NMR, 19F NMR, mass spectroscopy, and elemental analysis. Phase transition behavior was investigated by differential scanning calorimetry and polarized optical microscopy. Members of the two-ring series do not exhibit liquid crystalline phases. However, the three-ring analogues exhibit an enantiotropic SmA phase. When the length of alkyl chains is sufficient, an enantiotropic SmB phase is also identified.

Luminescent mesogen jacketed poly(1‐alkyne) bearing lateral terphenyl with hexyloxy tail

AbstractMesogen jacketed liquid crystalline poly(1‐alkyne) and poly(1‐phenyl‐1‐alkyne) linked pendants of terphenyl mesogens with hexyloxy tails at the waist position ({RCC [(CH2)3OOC‐terpheyl‐(OC6H13)2]}n, where RH, PHATP(OC6)2; RC6H5, PPATP(OC6)2) were synthesized. The influences of structural variations on the thermal, mesomorphic, and luminescent properties were investigated. Polymerizations of all monomers are carried out by WCl6‐Ph4Sn catalysts successfully. The polymers are stable (Td ≥ 340 °C) and soluble in common solvents. The monomers and polymers show enantiotropic SmA phases in the heating and cooling processes, and the lateral side chains of the mesogenic units are perpendicular to the main chain. The “jacket effect” of chromophoric terphenyl core “shell” around the main chain also contributes to polymers with high photoluminescence, and the pendant‐to‐backbone energy transfer path is involved in the luminescence process of this polymers. In comparison with monosubstituted polyacetylene PHATP(OC6)2, the disubstituted polyacetylene PPATP(OC6)2 shows better photoluminescence in both THF solution and film, and exhibited about 40 nm red‐shifted than PHATP(OC6)2, indicating that the “jacket effect” of terphenyl mesogens forces poly(1‐phenyl‐1‐alkyne) backbone to extend in a more planar conformation with a better conjugation. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010

Effects of substitution and terminal groups for liquid-crystallinity enhanced luminescence of disubstituted polyacetylenes carrying chromophoric terphenyl pendants

Liquid-crystalline and light-emitting poly(2-alkyne)s containing terphenyl cores with hexamethyleneoxy spacers, and cyano or n-propoxy tails −“[CH3C=C(CH2)6O-terphenyl-R]” n −, where R=CN, CH3PA6CN, R=OCH2CH2CH3, CH3PA6OPr, were synthesized. The effects of the substitution and terminal groups on the properties, especially the mesomorphic and optical properties of the polymers, were investigated. The disubstituted acetylene monomers (CH3A6CN, CH3A6OPr) were prepared through multistep reaction routes and were polymerized by WCl6-Ph4Sn in good yields (up to 82%). All the monomers and CH3PA6CN exhibited the enantiotropic SmA phase with a monolayer arrangement at elevated temperatures, whereas CH3PA6OPr formed a bilayer SmAd packing arrangement. Upon excitation at 330 nm, strong UV and blue emission peaks at 362 and 411 nm were observed in CH3PA6OPr and CH3PA6CN, respectively. The luminescent properties of CH3PA6CN and CH3PA6OPr have been improved by introducing the methyl substituted group, and the quantum yield of the polymer with cyano tail CH3PA6CN (Φ = 74%) was found to be higher than that of CH3PA6OPr (Φ = 60%). Compared to polyacetylene parents, both CH3PA6OPr and CH3PA6CN showed a narrower energy gap. This demonstrated that the electrical conductivities of polyacetylenes could be enhanced by attaching appropriate pendants to the conjugated polyene backbones.

Synthesis and Mesomorphic Properties of Some Chiral Fluorinated Benzoates

One series of chiral fluorinated benzoates have been synthesized. These compounds were characterized by IR, 1H NMR, 19F NMR, MS, and elemental analysis. Their phase transition behavior was investigated by DSC and polarizing optical microscopy. Generally, they show an enantiotropic SmA phase. The effect of lateral and terminal fluoro-substitution was studied in this series.

Mesomorphism of Four-Coordinated Four-Chained Metal Complexes Based on Pyrazolylpyridine Derivatives

A homologous series of four-chained silver(I) and zinc(II) metal complexes based on the coordination of two N N′-bidentate ligands pzR2py 2-[3,5-bis(4-alkyloxy)phenyl]pyrazol-1-yl]pyridine (R = C6H4OCnH2n+1, n = 16, 18) have been synthesised. All compounds [M(pzR2py)2][A]m (M = Ag, m = 1, n = 16, 18, (1,2), (3,4), CF3 (OTf–) (5,6), (7,8); M = Zn, m = 2, n = 16, 18, (9,10)) exhibit liquid crystal properties showing enantiotropic SmA phases, independently of the starting pzR2py ligands (non-mesomorphism for n = 18 or monotropic liquid crystal for n = 16), as well as the coordination geometry. The silver(I) derivatives [Ag(pzR2py)2]+ containing and as counteranions (1–4) are four-coordinated cationic complexes, but those containing OTf– and (5–8) exhibit a five-coordinated metal environment with distorted base-square pyramidal/trigonal bipyramidal geometry involving the counteranion. For the zinc(II) related compounds [Zn(pzR2py)2][NO3]2 (9–10), the tetrahedral metal environment is also distorted by the presence of coordinative interactions with the groups. Neutral tetrahedral compounds [ZnCl2(pzR2py)] (R = C6H4OCnH2n+1, n = 16 (11), 18 (12), 1 (13)) have also been investigated. Crystal structure of the first member of this series with n = 1, [ZnCl2(pzAn2py)] (13), has been characterised by single crystal X-ray diffraction. The molecules adopt the tetrahedral coordination environment with a planar ZnNNCN core. That structure for the related compounds containing longer alkyloxy chains (11–12) suggests a rod-like molecular shape in agreement with their observed liquid crystal lamellar phases.