Lateral Substituents Research Articles

Preparation of new supramolecular liquid-crystalline polyesters containing 3-chloro-4-(alkoxy)benzoic acids

Supramolecular liquid-crystalline polyester complexes based on intermolecular hydrogen bonds between the carboxylic group and the pyridyl moieties was prepared by using non-liquid-crystalline H-donors, [3-chloro-4-(butyloxy)benzoic acid (2a), 3-chloro-4-(octyloxy)benzoic acid (2b), 3-chloro-4-(dodecyloxy)benzoic acid (2c) and 3-chloro-4-(tetradecyloxy)benzoic acid (2d)] and H-acceptor-polyester containing pyridyl units. Intermolecular hydrogen bond formation was confirmed by Fourier transform infrared spectroscopy. The liquid-crystalline behavior of the complex formed was established by differential scanning calorimetry (DSC) and polarizing optical microscopy (POM). The polyester complexes containing 2c and 2d donor components exhibit liquid crystalline mesophase and behave as side-chain liquid-crystalline polymers. Compared with unsubstituted parent acid, the presence of chloro group as a lateral substituent has a little negative effect on the induction of liquid crystallinity on the polyester complexes systems. The results show that the more stability of the obtained H-bonded complexes in comparison with analogues without 3-Cl substituents is due to the increased acidity of benzoic acid moiety.

Synthesis and properties of allyloxy-based biphenyl liquid crystals with multiple lateral fluoro substituents

Allyloxy-based biphenyl liquid crystals, composed of alkyl chain, trans-cyclohexane and biphenyl mesogenic cores, ethylene linking groups, lateral fluoro substituents and allyloxy terminal groups were prepared via a six-step reaction based on 4-alkylcyclohexanecarbonitrile. Their structures were confirmed via infrared spectrometry, mass spectra and nuclear magnetic resonance. The mesomorphic properties of the present compounds were investigated by differential scanning calorimetry and polarising optical microscopy. The compounds exhibited negative dielectric anisotropy from −3.36 to −4.29 and a broad nematic mesophase with low melting points and high clearing points. The effects of the allyloxy terminal group and the lateral fluoro substituents on the mesomorphic properties and negative dielectric anisotropies are discussed. The present allyloxy-based biphenyl liquid crystals have potential for use in liquid crystal display mixtures.

New Angular-Shaped and Isomerically Pure Anthradithiophene with Lateral Aliphatic Side Chains for Conjugated Polymers: Synthesis, Characterization, and Implications for Solution-Prossessed Organic Field-Effect Transistors and Photovoltaics

An isomerically pure anti-anthradithiophene (aADT) arranged in an angular shape is developed. Formation of the framework of aADT incorporating four lateral alkyl substituents was accomplished by a one-pot benzannulation via multiple Suzuki coupling. This newly designed 2,8-stannylated aADT monomer was copolymerized with a ditheniodiketopyrrolopyrrole (DPP) unit and a bithiophene unit, respectively, to furnish an alternating donor–acceptor copolymer poly(anthradithiophene-alt-dithienyldiketopyrrolopyrrole) (PaADTDPP) and a thiophene-rich poly(anthradithiophene-alt-bithiophene) (PaADTT). PaADTT with crystalline nature achieved a high FET mobility of 7.9 × 10–2 cm2 V–1 s–1 with an on–off ratio of 1.1 × 107. The photovoltaic device based on the PaADTDPP:PC71BM (1:2.5, w/w) blend exhibited a Voc of 0.66 V, a Jsc of 9.49 mA/cm2, and a FF of 58.4%, delivering a power conversion efficiency (PCE) of 3.66%. By adding 1.5 vol % 1-chloronaphthalene (CN) as a processing additive, the PCE can be improved to 4.24%. We demonstrated that these angular-shaped and alkylated aADT-based polymers have better organic photovoltaic (OPVs) and field-effect transistor (FETs) characteristics than the linear-shaped ADT-containing polymers.

Increased mesophase range in liquid crystalline crown ethers via lower molecular symmetry

Herein, we report the synthesis and characterisation of liquid crystalline crown ethers bearing central [15]crown-5, unsymmetric [18]crown-6 and [21]crown-7 with lateral o-terphenyl and triphenylene substituents. Comparison with similar derivatives of [12]crown-4, symmetric [18]crown-6 and [24]crown-8 revealed beneficial effects of symmetry reduction on the mesomorphic properties. Decreasing symmetry led to broader phases and melting points at lower temperatures.

Synthesis and mesomorphic properties of but-3-enyl-based fluorinated biphenyl liquid crystals

But-3-enyl-based fluorinated biphenyl liquid crystals, composed of alkyl chain, trans-cyclohexane and biphenyl mesogenic core, ethylene linking group, lateral fluoro substitute, and but-3-enyl terminal group, were prepared via nine step reactions based on 4-alkylcyclohexanecarboxylic acids, and their structures were confirmed via infrared spectrometry, nuclear magnetic resonance, and mass spectrometry. The mesomorphic properties of these compounds were investigated by differential scanning calorimetry and polarising optical microscopy. The results showed that these compounds exhibited a broad nematic mesophase with low melting points and high clearing points. The effects of the but-3-enyl terminal group and the lateral fluoro substituent on the mesomorphic properties were discussed. These but-3-enyl-based biphenyl liquid crystals have potential for use in liquid crystal display mixtures.

Laterally substituted symmetric and nonsymmetric salicylideneimine-based bent-core mesogens

Bent-core mesogens have gained considerable importance due to their ability to form new mesophases with unusual properties. Relationships between the chemical structure of bent-core molecules and the type and physical properties of the formed mesophases are relatively unknown in detail and differ strongly from those known for calamitic liquid crystals. In this paper symmetric and nonsymmetric five-ring salicylideneaniline-based bent-core mesogens are presented, and the effect of lateral substituents attached at the outer phenyl rings (F, Cl, Br) or the central phenyl ring (CH3) on the liquid-crystalline behaviour and on the physical properties is studied. Corresponding benzylideneaniline-based compounds were additionally prepared in order to study the influence of the intramolecular hydrogen bond. The occurring mesophases were investigated by differential scanning calorimetry, polarising microscopy, X-ray diffraction and dielectric and electro-optical measurements. The paper reports on new findings with respect to the structure–property relationships of bent-core mesogens. On one hand, the disruptive effect of laterally substituted halogen atoms, F, Cl and Br, on the mesophase behaviour of three isomeric series was much lower than expected. On the other hand, an increase of the clearing temperature by 34 K was observed, caused by small lateral substituents. The electro-optical behaviour, especially the type of polar switching and corresponding molecular movements, is sensitive to variations in the molecular structure.

Synthesis, Structure, and Properties of Alkyl-Substituted PPXs by Chemical Vapor Deposition for Stent Coatings

High-molecular-weight un-cross-linked poly(p-xylylene) (PPX) derivatives (3) with one lateral linear alkyl substituent (methyl–octyl) on each phenylene moiety were prepared by pyrolysis of corresponding paracyclophanes followed by chemical vapor deposition (CVD). Most of these PPX derivatives showed good solubility in organic solvents which allowed purification by reprecipitation, structural analysis by solution NMR techniques, and molecular weight analysis by gel permeation chromatography. High thermal stability of 3 was found by thermogravimetric analysis. The glass transition temperatures decreased systematically with increasing alkyl chain length from 53 to −23 °C. Increased elongation to break up to 380% was analyzed by stress–strain experiments for as-deposited films indicating excellent coating properties, which were proven by initial coating tests on stents.

The locally polar smectic A phase in V-shaped molecules

For focusing on the polar smectic A phase derived from the V-shaped molecules, bent-core molecules with an acute-angled central core (Ar = 1,2-phenylene or 2,3-naphthylene) and a lateral halogen substituent (X = F or Cl) were synthesized. Their mesomorphic properties were investigated by DSC, polarizing microscopy, X-ray and electro-optical measurements. We found that a compound with Ar/X = 2,3-naphthylene/Cl forms the conventional smectic A phase, whereas three compounds with Ar/X = 1,2-phenylene/F, 1,2-phenylene/Cl and 2,3-naphthylene/F form the locally polar smectic A phase (SmAPR). According to our knowledge this is the first obvious experimental evidence that V-shaped molecules with an acute-subtended angled central core, in cooperation with a lateral halogen substituent, can form the SmAPR.

Increasing the flexoelastic ratio of liquid crystals using highly fluorinated ester-linked bimesogens

We present experimental results on the bulk flexoelectric coefficients e and effective elastic coefficients K of non-symmetric bimesogenic liquid crystals when the number of terminal and lateral fluoro substituents is increased. These coefficients are of importance because the flexoelastic ratio e/K governs the magnitude of flexoelectro-optic switching in chiral nematic liquid crystals. The study is carried out for two different types of linkage in the flexible spacer chain that connects the separate mesogenic units: these are either an ether or an ester unit. It is found that increasing the number of fluorine atoms on the mesogenic units typically leads to a small increase in e and a decrease in K, resulting in an enhancement of e/K. The most dramatic increase in e/K, however, is observed when the linking group is changed from ether to ester units, which can largely be attributed to an increase in e. Increasing the number of fluorine atoms does, however, increase the viscoelastic ratio and therefore leads to a concomitant increase in the response time. This is observed for both types of linkage, although the ester-linked compounds exhibit smaller viscoelastic ratios compared with their ether-linked counterparts. Highly fluorinated ester-linked compounds are also found to exhibit lower transition temperatures and dielectric anisotropies. As a result, these compounds are promising materials for use in electro-optic devices.

Phosphorescent, liquid-crystalline complexes of platinum(ii): influence of the β-diketonate co-ligand on mesomorphism and emission properties

Two series of rod-like ortho-platinated complexes bound to a range of β-diketonate co-ligands are reported of the form [Pt(N^C)(O^O)]. The liquid crystal and luminescent properties are influenced through the introduction of different β-diketonates (O^O) as well as through the presence of a fused cyclopentene ring on the N^C-coordinated 2-phenylpyridine ligand. For metal complexes, smectic phases are dominant but no mesomorphism is exhibited when the β-diketonate is hexafluorinated acetylacetonate (1,1,1-5,5,5-hexafluoro-2,4-pentandione). The introduction of an unsymmetrical trifluoroacetyl acetonate (1,1,1-trifluoro-2,4-pentandione) ligand is particularly interesting due to the discovery of the β-diketonate as a dynamic system that readily isomerises to a 1:1 ratio under thermal conditions, from an initial ratio of 3:1 formed during the synthesis. As expected, the presence of the 3,5-heptanedionato co-ligand decreases the transition temperatures due to the introduction of a larger lateral substituent. Unfortunately complexes based on 2-phenylpyridine ligands with a fused cyclopentene ring are, with one exception, not mesomorphic. With the exception of the hexafluoroacetyl acetonate complexes, the materials are brightly luminescent and have excited state lifetimes between 13 and 30 μs with emission quantum efficiencies exceeding 0.5, with one as high as 0.7. A time-dependent density functional theory (TD-DFT) study suggests that the lack of emission from the hexafluoroacetyl acetonate complexes may be associated with large structural distortion upon formation of the excited state, as well as to poorer overlap of orbitals leading to a lower radiative rate constant. The same analysis provides an explanation for the apparently quite different emission efficiencies of the two isomers of the trifluoroacetyl acetonate complexes.

Highly Flexible Poly(ethyl‐2‐cyanoacrylate) Based Materials Obtained by Incorporation of Oligo(ethylene glycol)diglycidylether

AbstractPoly(ethyl‐2‐cyanoacrylate) (PECA) is a polymer with potential medical or technical applications, which are limited due to its high brittleness. In this work, the capability of different ethylene or propylene glycol‐based oligomers to provide flexible poly(ethyl‐2‐cyanoacrylate) films upon blending is analyzed. The used oligoethers have been chosen with different end groups or lateral substituents and their effects the on macroscopic behavior of the obtained materials have been characterized. During its synthesis, in situ blending of PECA was performed with increasing quantities of oligo(ethylene glycol) diglycidyl ether providing homogeneously miscible materials with single Tg's. The Tg's decreased in a concentration dependent manner and showed negative deviation from predictions by the Fox equation, possibly due to specific intermolecular interactions. Remarkably, the mechanical properties could be tailored over a wide range with Young's moduli of 0.2 to 900 MPa, which so far has not been reported for cyanoacrylate‐based materials. Therefore, the concept of compatible blends should be further explored to establish flexible cyanoacrylate‐based materials for various technical or biomedical applications.

A direct route to polythiophenes displaying lateral substituents: Easy one-step synthesis and polymerization of thiophene monomers substituted by a dimethylenecarboxylate (CH2CH2COOR) appendage on the 3-position

Thiophene monomers displaying a dimethylenecar- boxylate (CH2CH2COOR) substituent on the 3-position of the aromatic ring can be easily obtained and in one step from the electrochemically induced reaction of 3-bromothiophene with the corresponding acrylate (CH2=CHCOOR). The synthesis of the ethyl ester monomer, of related 2,5-dihalogenothiophenes, and their polymerization are reported. Despite the surprisingly low solubilities displayed by the polymers, a full spectroscopic characterization could be performed and the data fully analyzed. Oxidative polymerizations (FeCl3 or electropolymerization) yield a regioirregular polythiophene, with 60–70% of head-to-tail diads. Both experimental and theoretical results suggest that the nonconjugated ester plays a very minor role - if any - in the polymerizations under oxidative conditions, but has a significant influence on the polymer properties. Preliminary attempts to polymerize the dihalogenothiophenes under reductive conditions were hampered by the even lower solubilities exhibited by the regioregular oligomers.

Photoluminescence quenching effects of surface-modified gold nanoparticles on side-chain polymers containing pyridyl H-acceptors with various lateral polarities

In this study, we used photoluminescence (PL) quenching and transmission electron microscopy (TEM) to study the morphological behavior of hydrogen-bonded (H-bonded) supramolecular assemblies of luminescent H-acceptor polymers and H-donor gold nanoparticles (Au NPs). In fluorescence titration experiments, the lateral Me and MeO substituents on the fluorescent H-acceptor side-chain polymers PBOT1– PBOT3 and PBT1– PBT3 exhibited different electron-donating capabilities, thereby inducing different degrees of H-bonding and dipole–dipole interactions, as evidenced by effective fluorescence quenching upon the addition of surface-modified Au NPs bearing acid and acid-free surfactants ( AuSCOOH and AuSC10, respectively). Among all of our tested nanocomposites, the highest Stern–Volmer quenching constant ( K SV) was that obtained from the assembly of AuSCOOH with the homopolymer PBOT1. In addition, we developed fittable exponential equations to predict the values of K SV of other fluorescent polymers (containing various molar ratios of pyridyl conjugated units) when titrated with these NP quenchers. The morphologies observed in the TEM images confirmed that fluorescence quenching resulted from the self-assembly of the supramolecular nanocomposites, mediated by H-bonds between the fluorescent H-acceptors of the polymers and the H-donors of the Au NPs presenting acid-modified surfactants.

Structure of the Major O-Specific Polysaccharide from the Lipopolysaccharide of Pseudomonas fluorescens BIM B-582: Identification of 4-Deoxy-d-xylo-hexose As a Component of Bacterial Polysaccharides

A novel constituent of bacterial polysaccharides, 4-deoxy-D-xylo-hexose (D-4dxylHex), was found in the major O-specific polysaccharide from the lipopolysaccharide of Pseudomonas fluorescens BIM B-582. D-4dxylHex was isolated in the free state by paper chromatography after full acid hydrolysis of the polysaccharide and identified by GLC-mass spectrometry, 1H and 13C NMR spectroscopy, and specific rotation. It occurs as a lateral substituent in ∼40% of the oligosaccharide repeating units, making the polysaccharide devoid of strict regularity. The structure of the polysaccharide was established by sugar analysis, Smith degradation, and two-dimensional 1H and 13C NMR spectroscopy. In addition, a minor polysaccharide was isolated from the same lipopolysaccharide and found to contain 4-O-methylrhamnose.

Modification of Filled, Rigid PVC Composites with Polyorganosiloxane

This article looks at the impact of a modifying addition of liquid polyorganosiloxane containing extended alkyl lateral substituents (PENTA-1006) as process lubricant in chalk-filled PVC composites. Demonstrates that this is a good universal process lubricant which improves the conditions for and reduces the energy input into processes of mixing and extrusion of rigid, chalk-filled PVC composites. The strength of the composites is not lessened by this and their material deformation characteristics are significantly improved.

Effect of Lateral Fluorine Substituent on Mesophase Behavior of Bent-shaped Molecules with Asymmetric Central Naphthalene Core

Abstract Novel lateral fluorinated bent-shaped molecules based on 1,7- and 1,6-naphthalene central core are prepared. Their mesomorphic properties are discussed in comparison with those of conventional unsubstituted bent-shape molecules.

Effect of dipole moment and conformation on the mesophase behavior of di-laterally substituted phenylazophenyl benzoate liquid crystals

The dipole moments of the previously prepared 4-(3′-fluoro phenylazo)-2-(or 3-) substituted phenyl-4′′-alkoxybenzoates ( I n a–d), have been determined in benzene at 30 °C. The data obtained were compared with those theoretically calculated by molecular modeling program to deduce the most probable conformations for each individual homologous series. Probable conformations deduced were found to vary according to type and position of the lateral substituent attached to the central benzene ring. The results were used to correlate the mesophase behavior, in pure and mixed derivatives, with the conformation deduced for each series. Each homologous series, that have in common a lateral fluorine atom on the first terminal ring, differs from the other by a second lateral group substituted on the central ring. The latter group varies between 2-CH 3, 3-CH 3, 2-Cl and 3-CN groups. Within each homologous series, the number of carbons in the other terminal alkoxy group varies between 8 and 16 carbons. The study aims to investigate the steric effect of the spatial orientation of the central lateral substituent, based on deduced conformations, on the mesomorphic properties in their pure or mixed states. The mesophase behavior was investigated via differential scanning calorimetry, DSC, and mesophases identified by polarized light microscopy, PLM.

Nonsymmetric bent-core liquid crystals based on a 1,3,4-thiadiazole core unit and their nematic mesomorphism

The synthesis and thermotropic properties of novel V-shaped molecules having a central 1,3,4-thiadiazole core with a bend-angle of 160° are reported. The compounds consist of a shape-persistent oligo(phenylene ethynylene) scaffold with lateral alkyloxy substituents. One of the terminal aromatic units possesses an alkoxy chain capped by an ethyl ester group while the second terminus is a pyridyl group. They exhibit enantiotropic nematic phases and are characterized by polarized optical microscopy, differential scanning calorimetry, and X-ray diffraction. Results from conoscopy indicate a biaxial nature of the nematic phase near room temperature. DFT calculations of dipole moments and molecular polarizabilities are used to substantiate the experimental findings.

Remarkable effect of a lateral substituent on the molecular ordering of chiral liquid crystal phases: A novel bromo-containing dichiralcompound showing SmC* variants

A bromo-substituted chiral smectic liquid crystal was synthesized for the purpose of the study on the sub-phases of the chiral smectic C* (SmC* variants) using resonant X-ray scattering. The introduction of a bromo atom was found to have a significant effect on the phase sequence. The bromo-substituted compound exhibited enantiotropic smectic phases in a wide temperature range of more than 130 K, in which at least five SmC* variants appeared below the smectic A phase. On the basis of the electro-optic and dielectric measurements, each SmC* variant was identified and assigned, and the structures of which were investigated by resonant X-ray scattering.

Antiferroelectric Behaviors of the SmCP Phase in Liquid-Crystalline Compounds with Achiral Bent-Core Liquid-Crystalline Molecules Containing Salicylaldimine-Based

A new series of bent-shaped mesogens has been synthesized and their mesomorphic properties studied. All compounds exhibit the B2 (SmCP) phase. Compounds with a 3,4′-biphenyldiol central core containing salicylaldimine-based and two terminal tetradecyloxy tails are reported. In addition, the effects of lateral substituent (R˭F and Cl) at the biphenyl core into 3′-position are examined. These substituents have a strong influence in reducing the clearing temperatures and increasing temperature range of the SmCP phase. The electro-optical switching characteristics have been investigated using both triangular-wave and DC electric fields. For several compounds, chirality switching from racemic to the homochiral state was seen after application of a low-frequency AC field. We studied spontaneous polarization, switching time, tilt angle, switching time, voltage-transmittance effect, and dielectric parameters (namely dielectric strength, relaxation frequency, distribution parameter) of a 7.5-µm-thick planar-oriented sample of a highly tilted anti-ferroelectric liquid-crystal material and investigated the correlation between their electro-optical properties and the chemical structures of these compounds.