Mesomorphic Properties Research Articles

Discotic liquid crystals of transition metal complexes 59 : Parity effect of the number of d-electrons on the columnar mesomorphism and homeotropic alignment of 1,4-diazatriphenylenocyaninato metal(II) complexes

Twenty super-discotic liquid crystals based on a largely expanded [Formula: see text]-conjugated macrocycle of 1,4-diazatriphenylenocyaninato metal(II) complex, (abbreviated as (C[Formula: see text]O)[Formula: see text]TzM: M = Co(1), Ni(2), Cu(3), Zn(4); [Formula: see text] = 8(a), 10(b), 12(c), 14(d), 16(e)) were synthesized in order to investigate their mesomorphism and homeotropic alignment properties by using polarization microscopic observations, differential calorimetry, thermogravimetry, and temperature-variable X-ray diffraction. As a result, the (C[Formula: see text]O)[Formula: see text]TzCo and (C[Formula: see text]O)[Formula: see text]TzCu complexes with an odd number of [Formula: see text]-electrons in the central metal ions showed a tetragonal columnar (Col[Formula: see text] mesophase for [Formula: see text] = 8[Formula: see text]14, which exhibit spontaneous homeotropic alignment for a very wide temperature range from rt to the decomposition temperature at around 340[Formula: see text]C. On the other hand, the (C[Formula: see text]O)[Formula: see text]TzNi and (C[Formula: see text]O)[Formula: see text]TzZn complexes with an even number of [Formula: see text]-electrons in the central metal ions showed a rectangular columnar (Col[Formula: see text](P21/a[Formula: see text] mesophase for [Formula: see text] = 8[Formula: see text]16, which did not exhibit homeotropic alignment. As far as is known, such a unique parity effect of the number of [Formula: see text]-electrons on mesomorphism accompanied by homeotropic alignment has never been reported to date.

Synthesis, mesomorphic properties, and theoretical study of benzothiazole-aromatic molecules with ester- and azomethine-linking groups

ABSTRACT Two novel groups of rod-like molecules with benzothiazole-aromatic systems: one group (group A) having an ester linkage with different thioalkyl chain length and the other (group B) ester- and azomethine-linkages with methoxy groups in the tip of the molecules were synthesised. The structures of the synthesised compounds were confirmed by using physicochemical techniques such as 1H NMR, mass spectra, FT-IR spectra, melting points, and elemental analyses. Differential scanning calorimeter and polarising optical microscopy have been employed to verify their liquid crystalline behaviours and transition temperatures. All the synthesised compounds (groups A and B) showed enantiotropic nematic phase except the compound 13d showed the nematic phase in cooling only. The mesomorphic properties of the present compounds were compared with some other structurally related compounds to understand the chemical structure–mesophase properties relationship. The thermal range of nematic phase for the compounds (group A) were decreased with the increase of the thioalkyl chain length. The liquid crystalline properties of the compounds (group B) were greatly affected by the position of terminal methoxy groups. The change of the position of terminal methoxy groups in the compounds (group B) was theoretically studied to investigate if the theoretical calculations possess an agreement with the practical results.

Mesogens with four-benzene molecular core and two lactate units in the chiral chain

ABSTRACT We prepared and studied new series of mesogens with a molecular core based on two biphenyls connected via ester linkage, with the biphenyl in central part laterally substituted by a chlorine atom. The studied compounds have two lactate groups and methylbutyl in the chiral chain and they exhibit the SmA phase in a very broad temperature range. We pursued the mesomorphic property and confirmed the phase identification by X-ray measurements. Additionally, we compared the studied compounds with previously prepared analogous materials. In comparison with homologues with different positions of the lateral substitution, we attempted to explain modified mesomorphic properties and absence of tilted mesophases for the studied series. We performed ab-initio calculations and found that the dipole moment is oriented along the long molecular axis, so its small transversal component probably causes the stability of the SmA phase and lack of ferroelectricity or antiferroelectricity.

Optical and Thermal Investigations of New Schiff Base/Ester Systems in Pure and Mixed States.

New mesomorphic series, 4-hexadecyloxy phenyl-imino-4′-(3-methoxyphenyl)-4″-alkoxybenzoates (An), were prepared and investigated with different thermal and mesomorphic techniques. The synthesized homologous series constitutes four members that differ from each other in the terminal length of flexible chain (n) attached to phenyl ester moiety, which varies between n = 6, 8, 10, and 12 carbons. A lateral CH3O group is attached to the central benzene ring in the meta position with respect to the ester moiety. Molecular structures of all newly prepared homologues were elucidated via FT-IR, 1H and 13C NMR spectroscopy. Mesomorphic and thermal properties were examined by differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) and the mesophases identified by polarized optical microscopy (POM). DSC and POM examinations revealed that all members of the present series (An) exhibit a purely enantiotropic nematic (N) phase. Comparative evaluations and binary phase diagrams were established between the present homologues and their corresponding shorter one (Bn). The examination revealed that, the length of the flexible alkoxy chain incorporated into the phenylimino moiety is highly effective on the temperature range and stability of the mesophase observed. With respect to the binary mixtures An/Bn, the exhibited N phase showed to cover the whole composition range with eutectic behavior.

New-Generation Liquid Crystal Materials for Application in Infrared Region.

This study presents 13 new organic compounds with self-assembling behavior, which can be divided into two groups. The first synthesized group includes compounds based on 4′-(trifluoromethoxy)-[1,1′-biphenyl]-4-yl-4-(trifluoromethoxy) benzoate core, and the second includes compounds based on 4-((4-(trifluoromethoxy)phenyl)ethynyl)phenyl-4-(trifluoromethoxy) benzoate core. They differ in the number and location of the fluorine atom in the lateral position. Mesomorphic properties, phase transition enthalpies, refractive indices, birefringence, and MWIR (mid-wavelength infrared) spectral properties of the compounds were investigated, and the results were compared with currently used materials. The influence of the length of the core as well as type and position of substituents in the molecular core was analyzed. The lack of aliphatic protons in the molecular structure generated unique infrared properties.

Synthetic, Mesomorphic, and DFT Investigations of New Nematogenic Polar Naphthyl Benzoate Ester Derivatives.

Four new non-symmetrical derivatives based on central naphthalene moiety, 4-((4–(alkoxy)phenyl) diazenyl)naphthalen–1–yl 4–substitutedbenzoate (In/x), were prepared, and their properties were investigated experimentally and theoretically. The synthesized materials bear two wing groups: an alkoxy chain of differing proportionate length (n = 6 and 16 carbons) and one terminal attached to a polar group, X. Their molecular structures were elucidated via elemental analyses and FT-IR and NMR spectroscopy. Differential scanning calorimetry (DSC) and polarized optical microscopy (POM) were carried out to evaluate their mesomorphic properties. The results of the experimental investigations revealed that all the synthesized analogues possess only an enantiotropic nematic (N) mesophase with a high thermal stability and broad range. Density functional theory (DFT) calculations were in accordance with the experimental investigations and revealed that all prepared materials are to be linear and planar. Moreover, the rigidity of the molecule increased when an extra fused ring was inserted into the center of the structural shape, so its thermal and geometrical parameters were affected. Energy gap predictions confirmed that the I16/c derivative is more reactive than other compounds.

Synthesis, mesomorphic and geometrical approaches of new non-symmetrical system based on central naphthalene moiety

ABSTRACT New non-symmetrical homologues series based on central naphthalene moiety, (E)-4-(4-(hexyloxy phenyl diazenylnaphthalene-1-yl-4ʹ-alkoxybenzoate (I 6/n), were synthesised and their mesomorphic properties was investigated. The prepared group constitutes four homologues bearing two terminal alkoxy chains of different proportionation. Elemental analyses, FT-IR and NMR spectroscopy were carried out to elucidate their molecular structures. Examination of their mesomorphic properties, were conducted via differential scanning calorimetry (DSC) and polarised optical microscopy (POM). DSC and POM investigations indicated that all the synthesised homologues are monomorphic possessing the enantiotropic nematic (N) phase. A comparative study was conducted between the present investigated central naphthalene series (I 6/n) and their corresponding central benzene analogues (II 6/n). The results indicated that, the mesophase type and stability as well as the mesophase temperature are affected by the protrusion of the naphthalene group. Theoretical calculations are in accordance with the experimental values of the investigated series. Moreover, the location of naphthalene group in the centre of the molecular geometry, increases the rigidity of the molecule, thus affects their thermal and physical parameters. The experimentally determined nematic stability was correlated with the calculated parameters and the study reveals that there are many factors sharing together to different extents in the enhancement of the behaviour of the observed nematic phase, depending on the different proportionation of the terminal lengths.

Main-chain biodegradable liquid crystal materials base on diosgenin: synthesis and mesomorphism

ABSTRACT Reinforcing the stability of aliphatic carbonate is an intractable problem that the mesomorphism of the material still needs to solve today. Here, novel main-chain liquid crystal compounds with mesomorphism are designed via the bulk ring-opening polymerisation to improve the stability and mesomorphic properties. The compounds were synthesised by bulk copolymerisation reaction of the monomers and initiator. The monomers of the 1, 3-trimethylene carbonate and the d, l-lactide were initiated by the diosgenyl derivative, without adding any catalyst. The chemical structures of obtained compounds were characterised by FT-IR and 1H NMR. The mesomorphic behaviour of the materials was determined by polarising optical microscopy and X-ray diffraction measurement. The thermal performance was investigated by differential scanning calorimetry and thermo gravimetric analyser. The results indicated that the phase transition temperature of the obtained compounds can be adjusted by the variation content of the monomers, and the compounds displayed an enantiotropic smectic phase in the room-temperature.

Photoinduced Exfoliation of a Polymeric N‐Benzylideneaniline Liquid‐Crystalline Composite Based on a Photoisomerization‐Triggered Phase Transition

AbstractHydrogen‐bonded liquid crystalline polymer composites containing N‐benzylideneaniline (NBA) as a photoresponsive mesogenic unit are prepared. The mesomorphic properties of the composite decrease upon exposure to UV light because of trans‐to‐cis photoisomerization, which affects the adhesive properties and allows facile exfoliation. In addition, the destabilized phase spontaneously reverts to the initial state when UV light irradiation stops. After exfoliation, the composite can be rebonded to a glass substrate by heating above its melting point. This is the first observation of the phase transition of an NBA liquid crystalline polymer.

Electro-Optical and Photo Stabilization Study of Nematic Ternary Mixture.

Liquid crystal materials composed of mixed nematic compounds find broad use in liquid crystal displays and photonic applications. A ternary mixture formed from three different nematic compounds shows peculiar behavior such as tunable electro-optical properties dependent on the frequency of the driving voltage. The paper presents an analysis of the response time and phase retardation of a frequency tunable nematic liquid crystal mixture (under code name 5005). This material possesses high birefringence (Δn = 0.32 at 633 nm) as well as high dielectric anisotropy (Δε = 6.3 at 100 Hz). The unique property of the 5005 mixture is frequency-controlled phase modulation, as in a dual frequency liquid crystal, while dielectric anisotropy goes to zero instead of being negative at high frequencies. For each component of the mixture, details on mesomorphic properties and their role in the formulation of the mixture are reported. The 5005 mixture was characterized by multiple investigation techniques, such as temperature dependence dielectric anisotropy, transmittance measurements image polarizing microscopy, and UV stability.

Mesomorphic, optical, dielectric, and electro-optic properties of azo-ester materials: Effect of lateral methyl and terminal substituents

The effect of introducing a lateral methyl substituent and the two different alkoxy terminal groups on the mesophase behavior of three-benzene-ring molecular core of azo-ester compounds bearing 2-methylbutoxy unit on the opposite terminal side (C1–C6) were explored. Their structures were confirmed by several spectroscopic techniques (Fourier transform infrared spectroscopy, 1H and 13C nuclear magnetic resonance spectroscopy). The mesomorphic properties of these compounds were studied by differential scanning calorimetry, polarized optical microscopy, and small- and wide-angle X-ray scattering. Except for the un-substituted terminals (C1 and C4), all other derivatives are liquid crystalline, exhibiting enantiotropic nematic liquid crystal phase. The alteration of the alkoxy chain length from methoxy to butoxy at the phenyl ester terminal group (ring A) for each set of laterally-neat and laterally methyl-substituted mesogens decreases the nematic temperature range. A decrease in the mesophase temperature range is also observed when a lateral methyl substituent is incorporated into phenylazo ring of the mesogenic core (ring C). Optical study demonstrated that their absorption spectra are identical in shape due to the structural similarities of the mesogenic core. The corresponding fluorescence spectra exhibited blue-emission with the laterally methyl substituted compounds having a relatively higher fluorescence intensity compared to that of its laterally un-substituted analogues. Furthermore, the laterally methyl-substituted derivatives were subjected to the planar alignment and their dielectric and electro-optic properties were investigated. The nematic phase of the aligned samples shows antiferroelectric switching behavior with spontaneous polarization, Ps ~ 5 μC/cm2.

Synthesis and mesomorphic properties of new azo H-shaped liquid crystal compounds

ABSTRACT Using tartaric acid as the core, six azo H-shaped liquid crystal compounds M1-M6 with different terminal substituents were synthesised. All products were structurally well characterised by elemental analysis, 1HNMR, and FT-IR. The phase behaviours were investigated by means of polarised optical microscopy and differential scanning calorimetry. M1-M6 were thermotropic enantiotropic nematic liquid crystals. They all showed schlieren texture in the process of heating up, and exhibited spherulite texture in the process of cooling down. M1 and M4 whose terminal substitution was nitro had the widest liquid crystal range in the same series of liquid crystal compounds, which were 135.1°C and 96.1°C, respectively, under heating cycle and 167.4°C and 112.7°C, respectively, under cooling cycle. The results show that the terminal substituents and flexible chain have important influence on the mesogenic phase and range. With the increase of flexibility, the mesogenic range of liquid crystal compounds becomes smaller when the end groups are the same. And when the flexible chain is the same, the greater the induced and polarised force of the terminal substituents, the better the mesogenic properties of the liquid crystal compounds.

Multichiral liquid crystals based on terphenyl core laterally substituted by chlorine atom

We designed a new type of antiferroelectric liquid crystalline structure with versatile properties. For this purpose, we modified the previously studied liquid crystalline compounds based on terphenyl molecular core laterally substituted with a chlorine atom. Two lactate units were attached to the chiral chain with the aim to support antiferroelectric structures. We studied the mesomorphic properties of new compounds by means of texture observations under a polarised light microscope, by dielectric spectroscopy and electro-optical measurements. To confirm the phase identification, x-ray measurements were performed. We found that the studied compounds revealed a SmA*-SmC* phase sequence in a broad temperature range. We proved an antiferroelectric phase with orthoconic properties for selected structural modifications. Such valuable optical properties with the tilt angle about 45° promise a big potential for applications.

Synthesis and mesomorphic properties of bis ester derivatives of coumarin containing chalcone linkage

Bis ester derivatives of coumarin containing chalcone linkage with various terminal alkoxy groups were designed, synthesized and characterized. Compounds 11a-m were studied for their mesomorphic properties using polarizing optical microscope & differential scanning calorimetry and photophysical properties using UV-vis & fluorescence spectroscopy. In this particular homologous series, compounds having lower flexible alkoxy chains showed very good mesogenic property with nematic mesophase formation, while analogues with higher chains failed to show any liquid crystalline property. Compound 11a with methoxy group showed very good absorbance and fluorescence as compared to higher chain length analogues.

Synthesis, Mesomorphic and Computational Characterizations of Nematogenic Schiff Base Derivatives in Pure and Mixed State.

Homolog series based on three aromatic rings bearing terminal alkoxy chain of various lengths named 4-(4-(alkoxy)phenylimino)methyl)phenyl nicotinate (An) were synthesized. The alkoxy-chain length changed between 6, 8 and 16 carbons. Mesomorphic and optical properties were carried out via differential scanning calorimetry (DSC) and polarized optical microscopy (POM). Elemental analyses, FT-IR and NMR spectroscopy were carried out to elucidate the molecular structures of the prepared derivatives. Mesomorphic results indicated that all the synthesized homologs (An) are monomorphic possessing the nematic (N) phase enantiotropically with wide thermal stability. Computational simulations were measured via density functional theory (DFT) theoretical calculation tool. The estimated thermal and geometrical parameters are in agreement with the experimental data. By discussing the estimated parameters, it was found that the molecular architecture, dipole moment and the polarizability of the investigated compounds are highly affected by the length of the attached terminal flexible chain and the location of the nitrogen atom in the other terminal aromatic ring. Binary phase diagrams of two corresponding homologs with different proportionating terminals were constructed, and their binary phase physical properties were discussed in terms of the temperature range and stability of the N phase.

Synthesis, identification and study of mesomorphic properties of compounds containing two C2H2N2O rings

The novel compounds of 1,3,4-C2H2N2O were manufactured from the response of acid hydrazides with carboxylic acids using POCl3 under reflex. These compounds were obtained from many sequence reactions as in Scheme 1. Converted anasic acid to acorresponding ester and acid hydrazid. The acid hydrazide used as starting materials for synthesis new carboxylic acid [IV] via condensation the acid hydrazide with 4-aminobenzoic acid in POCl3 to yield compound [III]. Then, the later compound coupling with benzoic acid in suitable conditions to formation compound [IV]. Also this new carboxylic acid [IV]converted to a corresponding ester and acid hydrazide. Finally, the synthesized acid hydrazides [VI] reacted with different type of carboxylic acid in POCl3 to get new derivatives of 1, 3, 4-C2H2N2O in two synthetic routs. The novel compounds were identified by using FTIR, NMR and Mass spectroscopy. The behaviour of these derivatives was examined under OPM and DSC. Compounds [IV], [VIII]1 and [XI]aexhibited nematic mesophase, while the other compounds [V], [VI], [VIII]3, 4, 5, 8, 9 and [XI]b, c did not show any mesomorphic properties.

Retraction: Synthesis, identification and study of mesomorphic properties of compounds containing two C2H2N2O rings (IOP Conf. Ser.: Mater. Sci. Eng. 1145 012055)

This article (and all articles in the proceedings volume relating to the same conference) has been retracted by IOP Publishing following an extensive investigation in line with the COPE guidelines. This investigation has uncovered evidence of systematic manipulation of the publication process and considerable citation manipulation.IOP Publishing respectfully requests that readers consider all work within this volume potentially unreliable, as the volume has not been through a credible peer review process.IOP Publishing regrets that our usual quality checks did not identify these issues before publication, and have since put additional measures in place to try to prevent these issues from reoccurring. IOP Publishing wishes to credit anonymous whistleblowers and the Problematic Paper Screener [1] for bringing some of the above issues to our attention, prompting us to investigate further.[1] Cabanac G, Labbé C and Magazinov A 2021 arXiv:2107.06751v1 Retraction published: 23 February 2022

New Nitro-Laterally Substituted Azomethine Derivatives; Synthesis, Mesomorphic and Computational Characterizations.

Two new homologues series, based on two rings of the azomethine central group bearing the terminal alkoxy group of various chain lengths, were prepared. The alkoxy chain length varied between 6 and 16 carbons. The other terminal wing in the first series was the F atom, and the compound is named N-4-florobenzylidene-4-(alkoxy)benzenamine (In). The second group of compounds included a lateral NO2 substituent in addition to the terminal F atom, named N-(4-fluoro-3-nitrobenzylidene)-4-(alkyloxy)aniline (IIn). Mesomorphic and optical properties were carried out via differential scanning calorimetry (DSC) and polarized optical microscopy (POM). Elemental analyses, FT-IR, and NMR spectroscopy were carried out to elucidate the molecular structures of the synthesized groups. Mesomorphic investigations indicated that all the synthesized homologues (In) were monomorphic, possessing the smectic A (SmA) phase monotropically, while the second group (IIn) members were non-mesomorphic. The experimental data indicated that the formation of the mesophase is affected by the protrusion of the lateral nitro group. The disruption of the mesophase in the second group was attributed to the increase of its molecular width, which affects its lateral intermolecular interactions. The computational simulations were in agreement with the experimental data. On the other hand, the location of NO2 group within the molecular geometry increased the melting temperature of the molecule, and thus, affected their thermal and physical properties. By discussing the estimated parameters, it was found that the molecular architecture, the dipole moment, and the polarizability of the investigated compounds are highly affected by the electronic nature and position of the terminal and lateral substituents as well as their volumes.

Influence of different linkages on the mesomorphic properties of aromatic ring system liquid crystals

In order to study the effect of the central linkage on the mesomorphic behaviour of aromatic ring liquid crystals we have synthesized two homologues groups, group A includes compounds 1a-d and group B includes compounds 2a-e. Group A has azo, azomethine, azo-ester, and azomethine-ester central linkages whereas the group B has azomethine, ether-azomethine, heterocyclic, and methylene-azomethine central linkages. The synthesized compounds were identified and characterized by elemental analyses and spectroscopic methods (proton nuclear magnetic resonance and Fourier transform infrared). The mesomorphic properties were investigated by polarizing optical microscopy (POM) with a heating stage and differential scanning calorimetry (DSC) thermograms with an aim to investigate the influence of different types of linkages on the mesomorphic properties in such aromatic ring systems. The results revealed that the change of the central linkages has a crucial effect on the mesomorphic properties when compared to the influence of different types of linkages. We found that the synthesised compounds (1a-d) showed smectic phase with different thermal ranges, while the synthesised compounds (2a-e) showed nematic phase except the compounds 2c-e which did not exhibit any liquid crystalline phase.

Luminescent Ionic Liquid Crystals Based on Naphthalene‐Imidazolium Unit

AbstractIn this article, we describe an efficient synthetic pathway and the characterization of liquid crystal luminescent imidazolium salts based on a naphthalene unit. The luminescent imidazolium‐naphthalene rigid part is decorated with a benzyl group functionalized by two or three dodecyloxy chains. A crystalline structure shows unambiguously the segregation between the rigid ionic and flexible parts conducive to the emergence of mesomorphic properties. A complete thermotropic properties study of these salts has been carried out according to different anions. The alkyl tail number variation and therefore the amphipathic character (balance between hydrophilic/hydrophobic) makes it possible to induce liquid crystal state with different architectures of self‐organization in layers (Smectic A) or columns (Columnar hexagonal). Finally, the photophysical properties were measured in solution and in the solid state at room temperature and showed photoluminescence quantum yields around 20 %.