Lateral Substituents Research Articles

Synthesis and physical properties of tolane liquid crystals containing 2,3-difluorophenylene and terminated by a tetrahydropyran moiety

ABSTRACTFour series of tolane liquid crystals containing 2,3-difluorophenylene and terminated by a tetrahydropyran (THP) moiety have been synthesised via multistep reactions based on 4-alkylcyclohexanecarboxylic acids and 4-bromo-2,3-difluorophenol. Their properties were measured by differential scanning calorimetry, polarising optical microscopy, Abbe refractometer and an electrical constants instrument. The results show that the THP-based liquid crystals nT reveal a relatively high value of the birefringence, negative dielectric anisotropy, good solubility and a broad nematic mesophase. The effects of the terminal alkyl chain, the lateral fluoro substituents and the THP terminal group on the mesomorphic and physical properties are discussed. Meanwhile, density functional theory calculations of molecular conformation and polarisability were conducted to correlate the experimental findings.

Bent-shaped liquid crystals based on 4-substituted 3-hydroxybenzoic acid central core – Part II

ABSTRACTThe synthesis and mesomorphic properties of new series of bent-shaped liquid crystals are presented. The properties of the materials were tuned by the character of the lateral substituent in position 4 of the central aromatic ring and length of terminal alkyl chains. Further modification of physical properties was achieved by the introduction of an additional ester unit in the terminal alkyl chain. The physical properties of the studied materials were determined by differential scanning calorimetry, polarising optical microscopy and for selected compounds by x-ray diffraction. The influence of structural changes as well as the orientation of ester linkages (in comparison with previously described materials) is discussed. The addition of the fifth ester unit into the structure of the studied compounds leads to significant changes in their mesomorphic behaviour.

Correction: A polymeric membrane permeabilizer displaying densely packed arrays of crown ether lateral substituents

Correction for ‘A polymeric membrane permeabilizer displaying densely packed arrays of crown ether lateral substituents’ by Ming Liu et al., RSC Adv., 2012, 2, 8606–8609.

Photosensitive chiral self-assembling materials: significant effects of small lateral substituents

Substituent effects are correlated with thermal Z–E isomerization as a crucial factor for applications in azo-based materials.

The effects of lateral halogen substituents on the low-temperature cybotactic nematic phase in oxadiazole based bent-core liquid crystals

We have previously demonstrated that the incorporation of lateral methyl groups on oxadiazole-based liquid crystals leads to relatively low-temperature cybotactic nematic phases which, in some cases, supercool to room temperature. We report here the synthesis and phase behaviour of related compounds that possess lateral halogen groups and in some cases, lateral methyl groups as well. Derivatives with three lateral substituents (one halogen and two methyl groups) in a specific pattern supercool in the nematic phase to room temperature. As was the case with the previously reported trimethylated derivatives, the low-temperature nematic phase is glassy in nature. Two of the new trisubstituted derivatives (with bromo and chloro groups) remain in the nematic phase upon subsequent heating until transitioning to the isotropic phase indicating that the low-temperature nematic phase may be more stable than that shown by the trimethylated analogue. Preliminary X-ray diffraction analysis confirms the presence of a tilted cybotactic nematic phase. In addition, the splitting observed in the wide-angle scattering feature is indicative of enhanced local biaxial packing.

Ruthenium-Grafted Vinylhelicenes: Chiroptical Properties and Redox Switching.

The properties of mono- and bis-Ru-vinyl[6]helicene complexes (2 a and 2 b, respectively), recently synthesized by using molecular engineering of helicenes based on the grafting of lateral organometallic substituents on the π-helical backbone through a vinyl bridge, are presented. These helicene derivatives are thoroughly characterized, with special attention given to their chiroptical properties and redox switching activity. The UV/Vis and electronic circular dichroism (ECD) spectra of P and M enantiopure species, both in the neutral and oxidized states ([2 a](·+), [2 b](·+), and [2 b](2+)), are analyzed with the aid of quantum-chemical calculations. The extended π-conjugation facilitated by the vinyl moiety, clearly visible in the electronic structures of 2 a,b, introduces new active bands in the ECD spectra that consequently lead to a significant increase in optical rotation of Ru-vinylhelicenes compared with the organic precursors. The vibrational circular dichroism (VCD) spectra were measured and calculated for both the organic and organometallic species and constitute the first examples of VCD for metal-based helicene derivatives. Finally, the redox-triggered chiroptical switching activity of 2 a,b is examined in detail by using ECD spectroscopy. The modifications of the ECD spectra in the UV/Vis and NIR region are well reproduced and rationalized by calculations.

Mesophase behaviour of laterally di-fluoro-substituted four-ring compounds

Four new groups of the di-fluoro-substituted 4-(2′-(or 3′)-fluoro phenylazo)-2-(or 3-) fluoro phenyl-4″-alkoxyphenylazo benzoates (In–IVn) were prepared and investigated for their mesophase behaviour. An alkoxy group of variable chain length (n = 6, 10 and 14 carbons) is attached to the terminal phenylazo benzoate moiety, and two lateral fluoro substituents are attached individually with different orientations to the other two adjacent rings. The molecular structures of the prepared compounds were confirmed by Fourier transform infrared spectroscopy and 1H NMR spectroscopy. The study aims to investigate the steric effect of the spatial orientation and relative positions of the two lateral fluorine atoms on the mesomorphic properties in their pure states. The mesophase behaviour was investigated via differential scanning calorimetry and mesophases were identified by polarised light microscopy. The investigation shows that these compounds exhibit high enantiotropic mesophases (SmC and N) and broad mesophase temperature range. The type and stability of the mesophase depends on the length of the terminal alkoxy chain and the position the two fluoro substituents. A comparison between these investigated compounds with their corresponding three-ring analogues was discussed.

Improved mesophase stability of benzoxazole derivatives via dipole moment modification

By modifying the molecular dipole moments with lateral monofluorine substituent, improved mesophase stabilities were obtained for novel benzoxazole derivatives, 2-(4ʹ-alkoxy-3-fluorobiphenyl-4-yl)-benzoxazole liquid crystals (coded as nPPF(3)Bx). The series of nPPF(3)Bx with lateral monofluorine substituent ortho to benzoxazole group have larger calculated dipole moments by about 2 D than the corresponding fluorine-substituted analogs (compounds I) with lateral monofluorine ortho to alkoxy group; it is interesting to note that they show lower melting and clearing points but better mesophase stability with wider mesophase ranges for the molecules with both polar (NO2, Cl) and nonpolar (CH3, H) terminal groups. Meanwhile, compounds nPPF(3)Bx show greater red-shifted photoluminescence emissions than compounds I, which suggest that π–π interaction between molecules is reinforced by the enhanced dipole–dipole interaction caused by increased dipole moments. These results suggest that modification of the molecular dipole moment is an effective method to improve the mesophase stability of the classical mesogenic compounds.

Synthesis and the effect of 2,3-difluoro substitution on the properties of diarylacetylene terminated by an allyloxy group

A series of 2,3-difluoro tolane allyloxy-based liquid crystals (LCs), which are composed of the tolane unit, lateral fluoro substituents, alkoxy and allyloxy terminal groups, were synthesised with 4-bromo-2,3-difluorophenol as the starting material via a five-step reaction. Their structures were confirmed by infrared spectroscopy (IR), mass spectroscopy (MS) and nuclear magnetic resonance (NMR). The mesomorphic properties were investigated by differential scanning calorimetry (DSC) and polarising optical microscopy (POM). The dielectric measurement was performed using an independent analyser EC-1 and the birefringence was determined using an Abbe refractometer. The results reveal that LCs have large negative dielectric anisotropy and high birefringence, which are potentially important for the fast response displays and liquid crystal photonic devices (LCDs).

Preparation and properties of lateral monofluoro-substituted benzoxazole-based mesogenic compounds

A series of 2-(3ʹ-fluoro-4ʹ-alkoxy-1,1ʹ-biphenyl-4-yl)-benzoxazole liquid crystals (coded as nPF(3)PBx) were prepared, where a lateral fluorine substituent, as well as methyl, chlorine and nitro terminal groups, was introduced into the molecules to investigate the effects of different polar substituents on the liquid crystal properties. The mesomorphic and photophysical properties were investigated. The results show that compounds nPF(3)PBx have enantiotropic mesophases; meanwhile, they exhibit UV–vis absorption bands with maxima at 323–326 nm and photoluminescence emission peaks at 389–395 nm, respectively. It is noted that nPF(3)PBx with terminal polar groups or electron-withdrawing groups (NO2, Cl) display higher clearing temperatures and wider mesophase range than those of the corresponding homologues with terminal non-polar groups or electron-donating groups (CH3, H). Meanwhile, compared with two lateral fluorine-substituted analogues containing 3,5-difluorophenyl unit, lateral monofluoro-substituted nPF(3)PBx display enhanced mesophase range both in heating and cooling except for terminal methyl-substituted compounds, as well as show obvious red-shifted UV–vis absorption bands and photoluminescence emission, which are attributed to the enhanced dipole–dipole interaction caused by increased dipole moment.

Paper No S3.2: Chiral Mesomorphic Compounds and Materials for Display Applications

AbstractIn this paper, we describe the effect of the molecular structure of chiral anisotropic compounds and materials on their mesomorphic and physico chemical properties. Modifications of the molecules via cyclic and bridge fragments or via lateral substituents allowed the preparation and optimization of specific mixtures for different display applications. The formation of defect free layers in ferroelectric liquid crystals stable against various mechanical or temperature deformations was studied. A new electro‐optic effect based on chiral‐nematic mixtures for creating high‐speed devices with switching time less than 1 ms was developed.

Characterization and Biological Potency of Mono- to Tetra-Halogenated Carbazoles.

This paper deals with the characterization and aryl hydrocarbon receptor (AhR) agonist activities of a series of chlorinated, brominated, and mixed bromo/chlorocarbazoles, some of which have been identified in various environmental samples. Attention is directed here to the possibility that halogenated carbazoles may currently be emitted into the environment as a result of the production of carbazole-containing polymers present in a wide variety of electronic devices. We have found that any carbazole that is not substituted in the 1,3,6,8 positions may be lost during cleanup of environmental extracts if a multilayer column is utilized, as is common practice for polychlorinated dibenzo-p-dioxin (dioxin) and related compounds. In the present study, (1)H NMR spectral shift data for 11 relevant halogenated carbazoles are reported, along with their gas chromatographic separation and analysis by mass spectrometry. These characterization data allow for confident structural assignments and the derivation of possible correlations between structure and toxicity based on the halogenation patterns of the isomers investigated. Some halogenated carbazoles exhibit characteristics of persistent organic pollutants and their potential dioxin-like activity was further investigated. The structure-dependent induction of CYP1A1 and CYP1B1 gene expression in Ah-responsive MDA-MB-468 breast cancer cells by these carbazoles was similar to that observed for other dioxin-like compounds, and the magnitude of the fold induction responses for the most active halogenated carbazoles was similar to that observed for 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). 2,3,6,7-Tetrachlorocarbazole was one of the most active halogenated carbazoles and, like TCDD, contains 4 lateral substituents; however, the estimated relative effect potency for this compound (compared to TCDD) was 0.0001 and 0.0032, based on induction of CYP1A1 and CYP1B1 mRNA, respectively.

Reinforcement in the mechanical properties of shape memory liquid crystalline epoxy composites

ABSTRACTIn this work, novel thermoresponsive shape memory composites based on glass fiber and nanosilica‐modified liquid crystalline epoxies (LCEs) with lateral substituent were prepared and characterized. According to the comprehensive analysis of polarized optical microscopy, wide‐angle X‐ray diffraction measurements, and tan δ data, the orientation of mesogen units were hindered by the introduction of nanosilica and lateral substituents of liquid crystalline epoxies, so that additional physical cross‐links except for similar chemical cross‐links emerged with the introduction of surface‐treated nanosilica. And the increased cross‐links could enhance the shape memory properties of the composites which could recover to their original state quickly in a time shorter than 30 s with high shape fixing ratios (>96%) and high shape recovery ratios (>98%), which indicated the composites could be applied into self‐deployable structural materials. Moreover, the reinforcement in the dynamic storage moduli, tensile modulus, and the tensile strength and shape memory properties indicated that glass fiber and nanosilica‐modified shape memory liquid crystalline epoxy composites could be high‐performance composites and could be used as new candidates for aerospace smart materials. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 42616.

Polarity and steric effect of the lateral substituent on the mesophase behaviour of some newly prepared liquid crystals

Eight homologous series of 2- (or 3-) substituted phenyl 4ʹ-(4ʺ-alkoxy phenylazo) benzoates (Ina–h) were prepared in which, within each homologous series, the length of the terminal alkoxy group varies between 6, 8, 10 and 12 carbons, while the other substituent, X, is a laterally attached polar group that alternatively changed from CH3, H, F, Br and CN. Compounds prepared were characterised by infrared and 1H-NMR spectroscopy, and their mesophase behaviour investigated by differential scanning calorimetry and identified by polarised light microscopy. The results were discussed in terms of polarity and steric effects. The stability of the mesophase was correlated once with the dipolar anisotropy of the whole molecule and another with the dipolar anisotropy of the substituent, X. A comparative study was made between the investigated compounds and their previously prepared linear 4-substituted isomers, namely 4-substituted phenyl 4ʹ-(4ʺ-alkoxy phenylazo) benzoates (Ini–k).

Polyfunctional intermediates for the preparation of liquid-crystalline and anisotropic materials

This paper describes the polyfunctional intermediates for the preparation of various anisotropic and liquid-crystalline compounds with different combinations of cyclic, bridge, terminal fragments and lateral substituents. Both chiral and nonchiral nematic, smectic mesomorphic and anisotropic compounds can be prepared by the transformations of the corresponding 3,6-disubstituted cyclohex-2-enones, trans-2,5-disubstituted cyclohexanones, 3,5-disubstitiuted 2-isoxazolines, substituted cyclohex-2-enonyl 2-isoxazolines, 1,2-disubstitiuted cyclopropanols and substituted unsaturated epoxyketones.

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Abstract Two series of unsymmetric dimesogenic compounds containing a butylene or pentamethylene group as the flexible spacer were synthesized and their thermal and mesomorphic properties were studied. Mesogenic groups of the synthesized compounds consisted of a cholesteryl and an azobenzene group with lateral substituent. Chemical structures and mesomorphic properties of the synthesized compounds were investigated by FT-IR, 1 H-NMR, differential scanning calorimeter (DSC), and polarizing optical microscope (POM). All synthesized compounds, apart from D5-OCH 3 , showed enantiotropic liquid crystal phases. Compounds having an even number of carbon atoms in the flexible spacer exhibited wide mesophase temperature ranges and high isotropic transition temperatures. Regarding the effect of lateral substituents, compounds with bulky substituents exhibited decreased mesophase temperature ranges and isotropic transition temperatures, while those with polar substituents showed the increased thermal stability of the smectic phase.

Prospects of the Development of New Approaches of the Preparation of Anisotropic Compounds and Materials

New synthetic approaches for the preparation of various anisotropic and liquid-crystalline compounds with different combinations of cyclic, bridge, terminal fragments and lateral substituents are proposed and realized. Both chiral and nonchiral nematic, smectic mesomorphic and anisotropic compounds were prepared by the transformations of the corresponding 3,6-disubstituted cyclohex-2-enones, 2,5-disubstituted cyclohexanones, 5-substituted cyclohexan-1,3-diones, 1,2-disubstitiuted cyclopropanoles and 3,5-disubstitiuted 2-isoxazolines, substituted cyclohex-2-enonyl-2-isoxazolines.

The influence of lateral substituents on the occurrence of a transition between two polar smectic phases with antiferroelectric properties

The synthesis and mesomorphic properties of two homologous series of bent-core (BC) compounds derived from 2,7-dihydroxynaphthalene are reported. The two series differ from one another by an electron-withdrawing or an electron-donating lateral substituent on the middle phenyl ring of the arms of the BC. Very interestingly, contrasting results are obtained in which polar phases are observed in compounds containing a chloro substituent and apolar smectic C and nematic phases are obtained when this substituent is replaced by a methyl group. The mesophases have been characterised by using a combination of polarised light optical microscopy, differential scanning calorimetry, X-ray diffraction measurements, electro-optical and dielectric studies.

Synthesis, mesomorphic behaviour and optical anisotropy of some novel liquid crystals with lateral and terminal fluoro substituents and a 2,6-disubstituted naphthalene core

The synthesis, mesomorphic properties and optical anisotropy of a range of diphenylnaphthalenes are detailed. One phenyl ring contains two lateral ortho fluoro substituents, with either a terminal butoxy chain or a pentyl chain; in both cases, the other phenyl ring possesses one, two or three fluoro substituents at the end of the molecule. The synthesis of the materials was effected efficiently using a combination of low-temperature lithiations and Suzuki palladium-catalysed cross-coupling reactions. All six novel compounds exhibit the nematic phase at very high temperature (between 125°C and 245°C), particularly those with fewer lateral fluoro substituents, and all show a smectic A phase. The melting points are rather high, but those compounds with a terminal pentyl chain and more lateral fluoro substituents do have much lower melting points (around 100°C). As expected from naphthalene liquid crystals, the optical anisotropy (measured as extrapolated values at 25°C) is very high (0.27–0.35), particularly for those compounds with a terminal butoxy chain and fewer lateral fluoro substituents.

The effect of lateral fluorination on the properties of phenyl-tolane liquid crystals

Multifluorinated phenyl-tolane liquid crystals were synthesised by two steps cross-coupling reactions, and their structures were confirmed by nuclear magnetic resonance (NMR), mass spectra (MS) and infrared spectrometry (IR). All of these compounds show only nematic phase, and their melting points decrease dramatically with the introduction of lateral fluorine atom. The physical properties of the compounds were also evaluated. The extrapolated birefringence of the compounds are at the range of 0.32–0.37 at 589 nm, and the dielectric anisotropies exist between 3.1 and 20.6, and the rotational viscosities are as low as 63.7–130.7 mPa·s. With the increase of lateral fluorine substituents in the benzene ring, the Δε value increases tremendously while the clearing points, birefringence and rotational viscosity decrease. These compounds show good solubilities and are favourable to form eutectic mixtures. The effect of lateral fluorine atoms at different region of the core on the dielectric anisotropy and mesophase is also discussed.