Novel supramolecular columnar liquid crystals based on thiosemicarbazides

Novel liquid crystal materials based on 3,4-di-n-alkoxybenzoylthiosemicarbazides (3a–h, n = 5–10, 12, 14) were synthesised. The mesomorphic properties of these compounds were characterised and studied by differential scanning calorimetry, polarising optical microscopy and X-ray diffraction. Compound 3a did not show mesomorphic properties; 3b shows a monotropic hexagonal columnar (Col_h) phase. Compounds 3c–h display an enantiotropic Col_h phase. The mesomorphic properties were found to be dependent on the length of alkoxy side chains. In N,N-dimethylformamide solution, all the compounds displayed a room temperature emission with λ_max at 361–332 nm. A thermogravimetric analysis also was performed.     

The synthesis and mesomorphic behaviour of tetracatenar di-hydrazine derivatives

Symmetrical four-chained (tetracatenar) di-hydrazine derivatives, namely oxalyl N',N'-bis(3,4-dialkoxybenzoyl)-hydrazide (BFH-n, n?=?4, 6, 8, 10), were synthesised. Investigations on the liquid crystalline properties by differential scanning calorimetry (DSC), wide-angle X-ray diffraction (WAXD) and polarising optical microscopy (POM) showed that the di-hydrazine derivatives exhibited columnar mesophases and the symmetry of the mesophase changes from rectangular to hexagonal on increasing the temperature. The rectangular columnar mesophases of BFH-n (n?=?6, 8, 10) remained stable down to 10°C during cooling and the subsequent recrystallisation from the Col_r phase of BFH-n (n?=?6, 8, 10) was observed on the second heating runs. Furthermore, the average number of molecules packing in a column slice was estimated to be three, based on their X-ray diffraction results. Intermolecular hydrogen bonding between –C=O and ?N?H groups in crystalline and liquid crystalline phases was confirmed.     

Restudy of the unusual phase behavior of the mesogen-jacketed liquid crystal polymers

1 Introduction Liquid crystals (LC) are a state of order between crystals and liquids. They have imperfect long range orders of orientation and position. Thus, they can be fluid like a liquid and they can have anisotropic prop-erties like crystals. For th…     

Synthesis of new monodendrons,gallic acid derivatives,self- assembled in a columnar phase

This article describes the synthesis and liquid crystal properties of new compounds that are derived from gallic acid. All the compounds were characterised by ¹H and ¹³C nuclear magnetic resonance spectroscopy (¹H NMR and ¹³C NMR), Infrared spectroscopy (IR) and Elemental analysis (CHN). The mesophases of these compounds were characterised using polarising optical microscopy (POM), differential scanning calorimetry (DSC) and SAXS measurements. The morphology of the surface of the films was investigated using atomic force microscopy (AFM). Compounds 9 and 13, which remain in a supercooled state until room temperature, do not exhibit liquid crystalline behaviour. The other compounds (i.e., 5, 7 and 8) self-assemble into tubular supramolecular architectures generating hexagonal columnar (Col_h) mesophases, which was confirmed by SAXS measurements.     

官能化苯并菲盘状液晶的合成及不饱柔链对介晶性的影响

合成了12个含不饱和软链的苯并菲盘状液晶化合物,C18H6（OC5H11）6-x（OR）x（x=1,2,3）,R=-C3H6CH=CH2（a）,-C3H6C≡CH（b）,-C2H4OCH=CH2（c）.化合物结构通过核磁共振氢谱和高分辨质谱表征.化合物热致液晶性通过偏光显微镜（POM）,差视扫描热量法（DSC）,和X射线衍射（XRD）进行了研究.结果显示目标化合物呈现有序的六方柱状介晶相.端炔基链化合物b系列熔点最高.乙烯氧基柔链化合物c系列有最高的清亮点和最宽的介晶性温度范围,且随着不饱和醚链数的增多,清亮点明显升高.对称苯并菲化合物sym-C18H6（OC5H11）3（OR）3比不对称化合物asym-C18H6（OC5H11）3（OR）3具有更高的熔点和清亮点.乙烯氧基柔链可极化的偶极相互作用对液晶稳定性有较大贡献.     

Elliptical diffusion of dye in hexagonal columnar polycatenar mesophases

We have studied polycatenar compounds which exhibit hexagonal columnar mesophases. In the planar orientation of these mesophases, the elliptical diffusion of the dissolved dyes is visualized by taking several pictures of the sample. The diffusion ratio D// /D is deduced for these columnar mesophases. Furthermore, using a classical optical absorption technique, we present measurements of dye diffusion in the same mesophases. The diffusion constants are measured in two geometries, along and perpendicular to the columns. The diffusion anisotropy ratios are in agreement with those deduced from the ellipse axes. The structure of these new columnar mesophases exhibited by rod-like mesogens is compared with that of disk-like mesogens.     

Enhanced stability of the columnar matrix in a discotic liquid crystal by insertion of ZnO nanoparticles

An experimental characterisation of dispersions of ZnO nanoparticles (NPs) in the columnar matrix of a discotic liquid crystal has been carried out. Thermophysical properties have been investigated by absorbance spectroscopy, differential scanning calorimetry, polarising optical microscopy, dielectric measurements, dc conductivity, X-ray diffraction and infrared (IR) dichroism technique. The experimental results show that inclusion of ZnO NPs into the columnar matrix enhances the orientational order in the columnar phase and does not affect the two-dimensional hexagonal lattice. The alignment in homeotropic samples is also found to be better with the addition of the NPs. The real (?′) and imaginary parts (?′′) of the permittivity increase by a small amount in the dispersions. The order parameter measured using the IR dichroism technique in the face-on geometry (homeotropic alignment) shows an enhancement for the composite system. The dc conductivity is also found to increase by an order of magnitude by addition of the NPs. These results suggest an improved stacking of the disc-like molecules within the columns by the insertion of the ZnO NPs possessing high charge mobility. Such composite systems would be highly beneficial for potential applications such as organic conductors.     

Elliptical diffusion of dye in hexagonal columnar polycatenar mesophases

We have studied polycatenar compounds which exhibit hexagonal columnar mesophases. In the planar orientation of these mesophases, the elliptical diffusion of the dissolved dyes is visualized by taking several pictures of the sample. The diffusion ratio D// /D is deduced for these columnar mesophases. Furthermore, using a classical optical absorption technique, we present measurements of dye diffusion in the same mesophases. The diffusion constants are measured in two geometries, along and perpendicular to the columns. The diffusion anisotropy ratios are in agreement with those deduced from the ellipse axes. The structure of these new columnar mesophases exhibited by rod-like mesogens is compared with that of disk-like mesogens.     

From smectic to columnar phase of polypedal liquid crystals based on tetrathiafulvalene/1,3-dithiol-2-thione and cholesterol

Bipedal 1,3-dithiole-2-thiones attached two cholesteryl through a ω-thioalkanoyloxy spacer of varying length were synthesized. The bipedals were easily transformed to the appropriate tetrapedal tetrathiafulvalene derivatives by self-coupling reaction in net triethyl phosphite. All the synthesized compounds exhibit mesogenic phases in a wide temperature region, no crystallization but vitrifying to form glassy mesogens during cooling from the isotropic melt. The liquid crystals with shorter spacer (n=2-6) exhibited only a smectic A phase and those with the longest spacer (n=7) exhibited only a hexagonal columnar. In these series, the molecular packing depended on the length of spacers.     

Columnar liquid crystalline assembly of a U‐shaped molecular scaffold stabilized by covalent or noncovalent incorporation of aromatic molecules

We report on our serendipitous finding of the anomalous behavior of a novel liquid crystalline (LC) molecule U _H/H , containing a U‐shaped handle. While U _H/H itself shows a bicontinuous cubic (Cub_bi) phase, U _H/H in the presence of pyrene molecules as an external guest forms a hexagonal columnar (Col_h) phase without phase separation. Interestingly, even when the pyrene molecules were covalently attached to U _H/H ( U _Py/Py ), the molecule exhibited a Col_h phase, with a similar columnar geometry to that of U _H/H mixed with pyrene molecules (1–4 equiv.). This result means that no matter how the pyrene moieties are incorporated in the LC system, the resultant material exhibited a similar molecular assembly with a columnar geometry. This finding is interesting because U _H/H and pyrene molecules do not seem to have specific interactions or shape complementarity to form a columnar assembly, as in the case of U _Py/Py . © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019 , 57, 342–351     

Columnar bis(pyridinium) ionic liquid crystals derived from 4-hydroxypyridine: synthesis,mesomorphism and emission properties

A series of flexibly linked bis(pyridinium) salts with various counterions (Br^?, PF₆^?, BF₄^? and OTf-) was designed and prepared starting from corresponding N-alkylated 4-pyridones precursors with mesogenic 3,4,5-tris(alkyloxy)benzyl moieties (alkyl = dodecyl or tetradecyl). These salts were investigated for their liquid crystalline properties by a combination of differential scanning calorimetry, polarising optical microscopy and temperature-dependent powder X-ray diffraction (XRD). Their thermal stability was checked by thermogravimetric analysis. All bis(pyridinium) salts, except the triflate salt with shorter terminal carbon chain, display an enantiotropic liquid crystalline behaviour with a hexagonal columnar (Col_h) phase assigned on the basis of its characteristic texture and XRD studies. It was found that these luminescent bis(pyridinium) salts show weak emission in dichloromethane solutions at room temperature and a pronounced red-shifted emission in solid state. The emission properties of these bis(pyridinium) salts do not depend significantly on the nature of counterion employed.     

Columnar liquid crystals based on amino-1,3,4-thiadiazole derivatives

Novel liquid crystal materials base on amino-thiadiazoles, specifically 5-(3,4-di-, and/or 3,4,5-tri-n-alkoxy)phenyl-2-amino-1,3,4-thiadiazoles (3a–f, n?=?10, 12, 14) and 5-(3,4-di- and/or 3,4,5-tri-n-alkoxy)phenyl-2-(4-amino)phenyl-1,3,4-thiadiazoles (6a–f, n?=?10, 12, 14) were synthesised. The mesomorphic properties of these compounds were studied by differential scanning calorimetry and polarising optical microscopy. All the compounds in series 3a–f and series 6a–f display an enantiotropic columnar phase. The mesomorphic properties were found to be dependent on the number of the side alkoxy chains, and on the length of the rigid core, and on the position of the thiadiazole ring. The best results were obtained with compounds of series 3a–f.     

High-pressure phase transitions in liquid crystals

Simultaneous measurements of the rate of heat evolution and changes of the mechanical variable of a transformation such as volume or pressure, performed in a p-V-T controlled scanning calorimeter have been applied to investigations of phase transitions in liquid crystals. In the instrument, the phase transitions can be induced by a controlled change of pressure, volume or temperature under isothermal, isobaric or isochoric conditions respectively. The present investigations have ben performed on 4-n-penthyl-penthylthiol-4-decycloxybenzoate which demonstrates in the liquid crystal state a nematic and three smectic phases

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Zusammenfassung In einem p-V-T-kontrollierten Scanning Kalorimeter wurden zur Untersuchung der Phasenumwandlungen in Flüssigkeitskristallen simultane Messungen der Geschwindigkeit der Wärmeentwicklung und der Veränderungen von mechanischen Größen von Umwandlungen, wie z.B. von Volumen oder Druck durchgeführt. In diesem Gerät kann die Phasenumwandlung durch eine kontrollierte Veränderung von Druck, Volumen oder Temperatur unter isothermen, isobaren oder isochoren Bedingungen ausgelöst werden. Vorliegende Untersuchungen wurden an 4-n-Pentyl-phenylthiol-4-dezyloxybenzoat durchgeführt, welches im Flüssigkristallzustand eine nematische und drei smektische Phasen aufweist.

     

Ionic hexagonal columnar metallomesogens derived from tetrabenzo[b,f,j,n] [1,5,9,13]tetraazacyclohexadecine

A series of transition metal (Ni, Cu, Pd) complexes derived from macrocyclic tetrabenzo[b,f,j,n] [1,5,9,13]tetraazacyclohexadecine (TAAB) was synthesized and their mesomorphic properties studied by differential scanning calorimetry, polarized optical microscopy and X-ray powder diffraction (XRD). These compounds have eight alkoxy side chains attached around the central molecular core and form disc-like molecules. All the derivatives exhibited columnar mesophases over a wide range of temperature. The mesomorphic behaviour was found to be dependent on the incorporated metal and the carbon length of the alkoxy side chains. The clearing temperatures decreased in the order M = Ni > Pd > Cu; this decrease was probably due to the size of the metal ions. Some derivatives with shorter side chains (n = 10, 12) were room temperature liquid crystals. All compounds were found to exhibit hexagonal columnar (Col_h) phases which were confirmed by powder XRD.     

Effect of alkoxy terminal chain length on mesomorphism of 1,6-disubstituted pyrene-based hexacatenar liquid crystals: columnar phase control

Synthesis and mesophase-transition behaviors of six 1,6-disubstituted pyrene-based hexacatenar liquid crystals 1_n (n=8–18) are reported here. They were synthesized by the Sonogashira coupling between 1,6-diethynylpyrene and 2-bromothiophene bearing a trialkoxybenzoyl group. The phase-transition behavior was studied by differential scanning calorimetry and polarized optical microscopy; a few mesophase progressions, I–Col/I–X–Col and Col–Sm, were observed, where X was an optically isotropic but unidentified phase. The structures of Col_r, Col_h, and Sm phases were analyzed by the X-ray crystallography, and the effect of the terminal alkoxy chain length on the mesomorphism was evaluated.     

Polycatenar Mesogens with Various Degree of Flexibility of Molecular Structure

A series of newly synthesised rod‐like polycatenar mesogens forms columnar phases, with the number of molecules in the column cross section depending on the core rigidity. For non‐symmetric molecules, an additional density modulation, namely helical arrangement of molecules with a periodicity of approximately 10 molecular distances develops along the columns. For one of the compounds, a new type of columnar liquid crystal phase with 3D positional order is observed. Introducing a stilbene unit in the mesogenic core enhances the fluorescent properties of the compounds. In the hexagonal columnar phase, polarised light emission is observed.     

Columnar liquid crystalline benzenetrisamides with pendant 1,3,4-oxadiazole groups

Novel liquid crystal materials based on 1,3,5-benzenetrisamide derivatives with three pendant 2-phenyl-5-(mono-, di-, and/or tri-n-alkoxyphenyl)-1,3,4-oxadiazole arms (Ia–c, IIa–c) were prepared. The mesomorphic properties of these compounds were characterised and studied by differential scanning calorimetry, polarising optical microscopy and X-ray diffraction. The formation of a columnar mesophase was found to be dependent on the number of alkoxy side chains. The compounds Ib and IIb, with a total of six alkoxy chains, and compounds Ic and IIc, with nine alkoxy chains, exhibited an enantiotropic hexagonal columnar (Col_h ) phase with high isotropisation temperatures; however, compounds Ia and IIa with a total of three alkoxy chains formed a crystalline phase. Compounds IIb and c were room temperature liquid crystals.     

A room-temperature heptazine core discotic liquid crystal

Heptazine is the fundamental structural and functional unit of graphitic carbon nitrides and has a π-conjugated planar symmetry with semiconducting properties. Molecular self-assembly is one of the key factors to drive the electronic behaviour of π-conjugated organic molecules. To enhance the semiconductivity, heptazine is decorated at its active sites with 2,3,5-tris(dodecyloxy)aniline to get well-organised columnar packing. A novel heptazine-core room-temperature discotic liquid crystal (HDLC) with hexagonal columnar geometry is discovered. The molecular structure and mesomorphic properties of HDLC are investigated by ¹H-NMR, ¹³C-NMR, IR, polarised optical microscopy, differential scanning calorimetry and X-ray diffraction. Photophysical and electrochemical properties of HDLC are studied by UV–vis/fluorescence spectroscopy and cyclic voltammetry (CV), respectively. The energy band gap of HDLC estimated from CV at room temperature is 1.63 eV, which is much narrower than the previously reported band gap for heptazine derivatives. This decrease in the energy band can be attributed to the particular designing of HDLC for columnar packing. As a columnar liquid crystal providing a smooth path to the charge transport, HDLC with such a narrow energy band gap may find applications in organic electronics.     

The influence of sodium chloride and urea on chromonic liquid crystals formed by CI Acid Red 266

Chromonic liquid crystals are currently receiving renewed interest with particular attention on the Edicol Sunset Yellow (ESY)/water system, which forms columnar nematic and hexagonal phases. CI Acid red 266 is structurally fairly similar to ESY and also forms columnar nematic and hexagonal phases but at much lower concentrations (>1%). In this study, we have examined the influence of sodium chloride and urea on chromonic liquid crystals formed by CI acid red 266. The techniques employed were polarising microscopy, X-ray diffraction and ²H NMR. Sodium chloride moves the concentration at which mesophases form to higher values. Once formed, the mesophases are stable to slightly higher temperatures. Screening of the interstack electrostatic repulsions by added electrolyte appears to be responsible for the changes. Urea can be added in fairly large concentrations (up to 25 wt%) without significant changes in mesophase stability. X-ray diffraction measurements show that there is little change in the aggregate structure with added urea. NMR measurements on urea and water ordering show that urea has much larger order parameters than water. Both order parameters are much smaller than values reported for ESY, but this is simply because of the lower dye concentrations. The larger order parameters for urea appear to arise from some intercalation of urea into the acid red 266 stacks. There is no evidence for changes in ‘water structure’ by the addition of urea.