Synthesis and mesomorphic properties of novel high birefringence azobenzene liquid crystals with lateral fluorosubstituent

In order to obtain liquid crystals with high birefringence (Δn), four azobenzene compounds based on lateral fluorinated bistolane moieties with trifluoromethyl terminal groups were synthesized with Hagihara–Sonogashira cross-coupling reaction. The molecular structures of the compounds were confirmed by Fourier transform infrared, ¹H-nuclear magnetic resonance. The transition temperatures, optical textures, and optical anisotropies were determined by differential scanning calorimetry, polarizing optical microscopy. The effect of the alkyl substituents on liquid crystal behavior is discussed in detail. The compounds have showed higher birefringence values.     

Amphotropic Properties of Cyclic Scyllitol Hexaesters [1]

Abstract

The new Scyllitol hexaesters with cyclic fragments in lateral substituents of series 1 were synthesized and their thermo- and lyotropic properties (with various organic linear or cyclic solvents) have been studied. It was established that the presence of benzene fragments in the substituents of the scyllitol hexaesters (1a-e) reduces the ability of the mesophase formation. The cyclohexane unit instead (sf. 1f) increases the thermostability of mesophase. While using above mentioned solvents a lot of cases of the induction of mesomorphic properties for non-mesogenic compounds of series 1 have been described. With cyclic solvents lyotropic mesophases were induced in binary mixtures of the hexaester 1a which showed mesomorphic properties neither under thermotropic conditions nor in binary mixtures with linear alkanes.     

Conformation of two 1-benzenesulphonyl-2-oxo-5-alkylthiopyrrolidine cognition activators

The molecular structures of the cognition activators (±)1-benzenesulphonyl-2-oxo-5-ethylthiopyrrolidine (1) and (±)1-benzenesulphonyl-2-oxo-5-isopropylthiopyrrolidine (2) were determined by means of X-ray diffraction and semi-empirical quantum mechanical methods. The conformational properties of the compounds, in the solid state andin vacuo (free molecule), were compared with those of the corresponding oxygenated derivatives bearing, in position 5, ethoxy and isopropyloxy substituents, respectively. The molecular arrangements of (1) and (2) in the solid state are similar, with the exception of the side chain on C(5), and they are retained alsoin vacuo. Both present an envelope conformation of the five-membered ring, and the relative positions of the five- and six-membered rings look similar and parallel those of their oxygenated parents. Fromin vacuo calculations another low-energy arrangement seems to be possible, and a detailed examination of the side-chain freedom in (1) and (2) gives more insight in the conformational properties of the compounds.     

Highly Birefringent Nematic Liquid Crystals for Reflective STN Applications

Abstract

An important parameter of any LCD containing portable electronic device is a low power requirement. The reflective STN display mode offers a moderate to high information content display with low power consumption. One method to realise colour in this mode is to use a large retardation (dΔn) value in the cell. For a cell gap of 6 μm, and a retardation of ?1.5, a birefringence (Δn) of greater than +0.2 is necessary. To achieve such a value in an STN LC mixture, materials with broad nematic range, good solubility and a Δn value of <+0.25 are required.

A study of the trans-cyclohexyldifluorophenyltolane core structure was made and a large number of dialkyl, alkenyl-alkyl and alkoxy materials were synthesised and characterised. These materials possess low to moderate melting points, broad purely nematic mesophases, a high Δn and very good solubility in nematic LC hosts. They are suitable materials for inclusion in mixtures for colour reflective STN displays.     

Mesogenic 3,6-bis(4-hydroxyphenyl)-1,2,4,5-tetrazine alkanoate esters

A novel series of 3,6-bis(4-hdroxyphenyl)-1,2,4,5-tetrazine alkanoate esters were synthesized and their mesogenic properties were studied using differential scanning calorimetry (DSC) and polarizing optical microscopy (POM). The impact of changing the tail-core linkage from alkyl or alkoxy to ester is profound. Compared to the alkyl or alkoxy linkages, the ester linkage reduced mesogenic properties. Short-tailed compounds are non mesogenic (4a-4e), while long-tailed compounds (4f-4r) exhibit nematic phases. Unlike the alkyl or alkoxy tail series, none of the 18 presented esters in this series exhibits a smectic phase.     

Electro-Optical Properties in Polymer-Stabilized Blue Phase of n-OCB Homologue Chiral Nematic Liquid Crystal Mixtures

In this study, the chemical structures and physical property dependencies of the electro-optical properties were investigated in polymer-stabilized blue phase (BP) using the four kinds of 4-n-alkyloxy-4′-cyanobiphenyl (n-OCB) homologue chiral nematic LCs. It was confirmed that the optical response time and Kerr coefficient in polymer-stabilized BP was varied with the molecular parity as determined by the alkyl chain length of the n-OCB homologue chiral nematic LC mixtures.     

Novel cyclotriveratrylene columnar liquid crystal with three alkyl chains: The balance between the number and length of alkyl chains for liquid crystalline behavior

Series of cyclotriveratrylene (CTV) derivatives with triazole ring and three alkyl groups were prepared by one-pot click condensation in yield of 80–88%. The structures and crown conformations were confirmed by NMR and MS. Their liquid crystalline properties were investigated by DSC, POM and XRD analysis. The studies on mesomorphic properties suggested that the CTV derivatives with pentyl, hexyl or dodecyl groups show no mesophase but the one with octadecyl groups possesses ordered hexagonal columnar mesophase. In comparison with the reported columnar CTV liquid crystals with six alkyl chains at least, the CTV columnar CTV liquid crystal with three alkyl chains was reported for the first time. These results suggested a subtle balance between the number and length of alkyl chains for columnar CTV liquid crystalline behavior.     

Properties of liquid crystals and Cu2+ recognition based on Schiff bases

Two series of new Schiff base compounds were synthesized. For Schiff base compounds with a pyridine nitrogen atom in 4-position (7a–e), their supramolecular hydrogen bonding complexes show good liquid crystal properties. However, no liquid crystal property is observed for 8a–e. Results of theoretical calculations demonstrate that it is the intermolecular hydrogen bond of Schiff base compounds (8a–e) that prevents the formation of supramolecular hydrogen bonding. The Schiff base compounds, with terminal alkoxy chains, can recognize Cu²⁺ selectively with a color change. Nevertheless, others cannot recognize Cu²⁺.     

First Truly Ferroelectric Liquid Crystal

The first faroelectric liquid crystalline phase (in 8SI* (ΔS-(+)-(4-(2′methylbuty1) phenyl-4′-n-octylbiphenyl-4 carboxylate) is reported and its physical properties are discussed. The close connection between the phase sequences of 8SI* and its racemate are established. Both compounds show a number of smectic phases above the newly discovered ferroelectric phase and its analogue in the racemate. These phases (CI and G') are tilted in the racemate 8SI and tilted with a helicoidal structure in 8SI*. In the truly ferroelectric phase, X, the director of the molecules can be oriented in a bistable way in an electric field Furthermore when the field is turned off the director orientation remains unchanged. This behaviar is fundamentally different from that in bulk smectic phases which support the helix structure in the absence of external forces. A model far ‘racemates’ in higher smectic phases like G, G', H’ etc as well as a the newly discovered ferroelectric phase is presented. The response of cholesteric blue phases of 8SI* to an external field is discussed in an appendix.     

Effects of aromatic core and flexible terminal chain structures on the properties of luminous liquid-crystalline gold(i) complexes for functional materials

ABSTRACT

Luminescent liquid-crystalline (LC) Au complexes with various aromatic cores and flexible terminal chains were synthesized. The aromatic core aspect ratio crucially affected the LC temperature range and melting point of the complexes. Moreover, branched flexible chains reduced the melting point, thus expanding the LC temperature range. In the crystalline and LC phases of the complexes, fluorescence was quenched by the aggregation-caused quenching effect, but phosphorescence was enhanced by the crystallization-induced phosphorescence effect. However, no phosphorescence was observed in the isotropic phase. Thus, not only aggregation but also regularity of molecular aggregates is necessary for the observed crystallization-induced phosphorescence effect.     

The X-ray Structures of Sulfones

Abstract  

The X-rays structures of diphenyl sulfone 1, bis(3-aminophenyl) sulfone 2, bis(4-nitrophenyl) sulfone 3, 2-nitrophenylphenyl sulfone 4, benzylphenzyl sulfone 5, 4-nitrobenzylphenyl sulfone 6, 4-methylphenylbenzyl sulfone 7, dibenzyl sulfone 8, benzylisopropyl sulfone 9, and methylacetate,ethyl sulfone 10, are reported. B3PW91 DFT calculations were performed on selected sulfones for comparison. The S = O distances in these compounds range from 1.392(5) to 1.463(3) Å and S–C bond distances range from 1.743(7) to 1.790(3) Å. The C–S–C bond angles vary from 101.1(3)° to 106.80(14)° and the O–S–O bond angles vary from 116.7(2)° to 120.61(8)°. Using data obtained here and comparison with published structural data no evidence was found for para substituents on aryl groups influencing S–O bond distances, however, small changes on S–C bond distances were noted. Additionally, if the sulfur is flanked by an alkyl group the S–C distance is slightly larger than when it is flanked by an aryl group. Most of the sulfone compounds studied here display intermolecular soft hydrogen bonding interactions which influence their solid state packing. Furthermore, in dialkyl sulfone compounds these interactions appear to be strong enough to overcome conformational barriers calculated to be ca. 6 kJ mol⁻¹.     

Fabrication of half-polyimide-less liquid crystal device with fast response using reactive self-aligning amphiphile

ABSTRACT

We propose a new vertical alignment method for fast switching liquid crystal displays (LCDs) without the polyimide alignment layer on one side of a substrate. The key to this new method is the use of the amphoteric 2-carboxyethyl acrylate, which combines reactive acrylate and carboxylic acid groups to allow hydrogen bonding with substrate. The reactive group can achieve pre-tilt for a fast-switching of LC molecule, and the hydrogen bonding allow for vertical alignment of LC. The amphoteric material enables the manufacturing of cost-effective LCDs by reducing the number of steps in the process and fast switching by establishing pre-tilt alignment.     

The Liquid Crystal Properties of Some Aromatic Esters Derived From Naphthalene

Abstract The 2,6-naphthylene ring system has been used to replace each of the 1,4-phenylene rings in various 4-substituted-phenyl 4-substituted-benzoates, where the substituents were alkyl and/or alkoxy. For the dialkyl esters, the N-I temperatures were increased by 60–80° compared with the simpler, analogous phenyl benzoates, irrespective of the position of the 2,6-naphthylene ring. For the esters with one alkyl and one alkoxy substituent, the N-I temperatures were again higher than those of the corresponding phenyl benzoates (～60°); S_A properties were quite pronounced in the 6-alkyl-2-naphthyl 4-alkoxybenzoates. When both substituents were alkoxy groups, S_C phases of quite wide thermal range were exhibited, usually preceded on cooling by a nematic and a S_A phase.     

Highly Dichroic Triphenodioxazine Dyes for Guest Host Liquid Crystalline Mixtures

Abstract

Novel triphenodioxazines have been synthesized and evaluated. The dyes were not only highly dichroic in guest-host liquid crystal mixtures but also vivid because of a sharp peak in absorption spectra. Mesogenic substituents to the 2,9- position of the chromophore improve the order parameter in the mixture. Moreover, the mixtures also showed significant polarized photoluminescence. These results would reveal a few advantages of the novel dyes for some possible applications.     

Synthesis and Mesomorphic Properties of New Columnar Liquid Crystal Containing 1,3,5-triiminebenzene with Pendant 1,3,4-thiadiazole Group

A novel discotic liquid crystal series based on 1,3,5-benzenetrisazomethine derivatives with three pendant 2-amino-5-(4′-n-alkoxy)phenyl-1,3,4-thiadiazole has been synthesized, which is the first columnar molecules containing 1,3,4-thiadiazole moiety exhibiting a discotic liquid crystal. The molecular structure of compounds was confirmed by FT-IR, ¹H-NMR, and mass spectroscopy and elemental analysis. The electron excitation properties of these compounds were investigated by UV-vis absorption spectroscopy. Their liquid crystalline properties were studied by polarizing optical microscopy and differential scanning calorimetry. The formation of a columnar mesophase was found to be dependent on the number of methylene unit in alkoxy side chains.     

Trans−1,2-Difluorostilbenes: Promising Materials for High Dielectric Biaxiality Ferroelectric Mixtures

Abstract

A range of two- and three-ring liquid crystals have been synthesised that incorporate a trans?1,2-difluoroethene linking group. Some of the materials have surprisingly low melting points and high smectic C phase stability, and they exhibit the ideal phase sequence for ferroelectric hosts of smectic C to smectic A to nematic. The synthesis was accomplished in a convergent manner through the use of low-temperature lithiations to generate organometallics based on boron and tin. Palladium-catalysed cross-couplings and Michael-type reactions were used to generate the final mesogenic materials. The polar fluoro substituents enable the generation of ferroelectric mixtures with a high dielectric biaxiality which is very important in τV minimum driving schemes. The alkenic linking group in stilbenes normally confers instability, but the difluoro-substituted analogues are stable compounds.     

The X-Ray Structures of Sulfoxides

Abstract  We have structurally characterized and investigated a range of sulfoxide compounds containing aryl and alkyl substituents. Compounds 1 and 3–6 all crystallize in an orthorhombic space group, where compounds 2 and 7 crystallize in a monoclinic space group. The unit cell parameters of the compounds are as follows: 1 (Fdd2), a = 17.653(5) ?, b = 53.153(14) ?, and c = 10.071(3) ?; 2 (P2 ₁ /c), a = 7.894(13) ?, b = 5.653(10) ?, and c = 27.02(5) ?, β = 97.347(15)°; 3 (P2 ₁ 2 ₁ 2 ₁ ), a = 5.7569(6) ?, b = 12.2139(12) ?, and c = 17.5974(18) ?; 4 (Pca2 ₁ ), a = 8.256(4) ?, b = 5.470(3) ?, and c = 23.995(13) ?; 5 (P2 ₁ 2 ₁ 2 ₁ ), a = 5.848(4) ?, b = 7.568(5) ?, and c = 27.650(17) ?; 6 (Pbca), a = 10.0569(15) ?, b = 9.9403(16) ?, and c = 17.843(3) ?; and 7 (Pc), a = 13.217(4) ?, b = 5.3766(14) ?, and c = 8.370(2) ?, β = 90.673(6)°. The S=O bond distances in these compounds range from 1.489(7) to 1.515(8) ?. In all seven structures, the O(1)–S–C bond angles vary from 105.1(4) to 111.7(30)° and the C(1)–S(1)–C(11) bond angles range from 94.1(4) to 100.56(12)°. The compounds contain unique intra- and intermolecular interactions depending on the groups attached to the sulfoxide moiety. The polarity of the sulfoxide bond in these compounds allows for intramolecular S···O interactions to occur. When the sulfur is bound to alkyl groups, there tends to be a shorter S···O intermolecular distance than when the sulfur is bound to aromatic substituents. Additionally, if the sulfur is flanked by an aryl group, the S–C bond distance is slightly shorter than if flanked by an alkyl group, suggesting a possible weak O···H_aryl intramolecular interaction, weak conjugation of the aromatic ring with the S–O bond or both. Furthermore, if the sulfur is flanked by an alkyl group, a CH₂ proton of S–CH₂–R can be properly oriented to participate in an intermolecular hydrogen bond with the sulfoxide oxygen of another molecule. Index Abstract  We have structurally characterized and investigated a range of sulfoxide compounds containing aryl and alkyl substituents that contain unique intra- and intermolecular interactions depending on the groups attached to the sulfoxide moiety.      

Alkyloxy azo-cinnamate ester based thermotropic liquid crystals and their photophysical investigations

Two series of rod shaped Schiff base containing azo-cinnamate thermotropic liquid crystalline compounds were synthesized and characterized. These molecules have four different alkyl spacers (n = 6, 8, 10, and 12) at one end and a dodecyloxy chain at another end (n = 12) which influence their liquid crystalline properties. Liquid crystallinity commence from six methylene spacer onwards in the series exhibiting with Nematic to Smectic-C mesophases. Analytical data confirm the molecular structures of homologues series of compounds. The characteristic texture of liquid crystalline phases obtained using polarizing‐light microscope with a heating stage. The structural transformation of these liquid crystals was confirmed by differential scanning calorimetry. All the compounds exhibited various calamitic mesophases with wide mesomorphic temperature ranges. The relationship between structure and mesomorphic properties was discussed in framework of geometrical configuration of central unit, linking part, and length of alkoxy chains. Photosensitive azobenzene group undergoes photoisomerization under UV light and monitored by UV-Visible spectroscopy.     

Glass Dispersed Liquid Crystals

Abstract

Liquid crystals can be trapped into inorganic (silica) substrates by sol-gel processes. The sol-gel process consists of hydrolysis and polycondensation reactions of metal organic monomers, i.e. organoalkoxy silanes, which allows the formation of a silica gel-glass. These processes have been used since 1984 for trapping organic molecules into inorganic oxides; usually, single molecules are trapped into isolated gel-glass (nm size) pores. However, it is possible, by chemical means, to induce larger (0.1–10 pm) cavities in the network of the gel-glass allowing the formation of embedded micron size droplets of low molecular weight nematic LC molecules. Surface variations in these cavities (e.g., providing a molecular oriented surface using Si-CH,CH, groups on the pore cage) may allow a lamellar structure and alignment of the nematogenic LC compounds at the surface. It was suggested that order arises as a consequence of the chemical affinity between the apolar character of the pore surface and the lipophilic groups of the LC. Therefore, the main concern has been to ascertain whether the sample manufacturing keeps the LC structure, thus giving gel-glass dispersed liquid crystals (GDLCs) with electrooptical response.     

Asymmetrical Azobenzene Liquid Crystals with High Birefringence Prepared via Click Chemistry

Asymmetrical azobenzene liquid crystals with high birefringence were prepared via the click chemistry method. The chemical structures of the synthetic intermediates and compounds were confirmed by FT-IR and ¹H-NMR. The liquid crystal behavior, including transition temperatures and phase sequences, were investigated by DSC and POM. The effect of the alkyl substituents on liquid crystal behavior is discussed in detail. Then, the birefringence values of the liquid crystals were measured using polarizing light interferometry method. Moreover, the characteristics of selective reflection, which was associated with the value of birefringence, were studied.