Hydrogen-bonded complexes between mesogenic heterocyclic Schiff's bases and mesogenic 4- n -nonyloxybenzoic acid: mesomorphic behaviour, FTIR study and PM3 semi-empirical calculations

A new series of intermolecular hydrogen-bonded complexes has been obtained using mesogenic 4- n -nonyloxybenzoic acid and mesogenic 5-(4-pyridyl)-2-(4- n -alkoxy) benzylideneamino-1,3,4-thiadiazole moieties. The thermal and phase behaviour of these complexes were studied by thermal microscopy and differential scanning calorimetry. Intermolecular hydrogen bonding was studied by FTIR spectroscopy, from crystalline to the isotropic state. A study by PM3 semi-empirical calculations is also described.     

Studies on thermotropic liquid crystalline polyurethanes. III. Synthesis and properties of polyurethane elastomers by using various mesogenic units as chain extender

Four series of thermotropic polyurethane elastomers (TPUEs) were synthesized in this study. The hard segments were formed by using 4,4′-methylenedicyclohexyl diisocyanate (H₁₂MDI) reacted with various mesogenic units, such as benzene-1,4-di(4-iminophenoxy-n-hexanol), benzene-1,4-di(4-iminophenol), and 3,3′-(4,4′-biphenylene)dipropanol, which also acted as the chain extender. Poly(oxytetramethylene)glycols (PTMEGs), PTMEG-2000 (M_n 2,000) and PTMEG-1000 (M_n 1,000) were used as a soft segment. The structures of all synthesized thermotropic liquid crystalline polyurethanes (TLCPUs) were characterized by FTIR spectroscopy. The effects of mesogenic units on the LC properties and elastic behaviors of LCPUs were studied. It was difficult to show LC behaviors for the PU elastomers derived from the mesogenic units with a lower aspect ratio, such as 3,3′-(4,4′-biphenylene)dipropanol, or the long soft segments, PTMEG-2000. In addition, these PU elastomers show better elastic properties by using a higher aspect ratio mesogenic unit as the chain extender, such as benzene-1,4-di(4-iminophenoxy-n-hexanol and benzene-1,4-di(4-imino-phenol)). The thermal properties were investigated by DSC measurements, thermal optical polarized microscopy, wide angle X-ray diffraction, dynamic mechanical analysis, and thermogravimetric analysis. The mechanical properties were measured by a tensilemeter. © 1996 John Wiley & Sons, Inc.     

Synthesis and thermal properties of diurethanes containing various mesogenic units

Abstract

Five homologous series of diurethanes containing mesogenic moieties were synthesized by addition reactions of ω-alkenols to aromatic diisocyanates. The thermal behaviour of the compounds was studied by differential scanning calorimetry and on the hot stage of a polarizing microscope. Thermotropic liquid crystal behaviour was found for the diurethanes having a central core of more than two aromatic rings. Smectic C mesophases were observed for the derivatives of 4,4″-p-terphenylene and nematic mesophases for the diurethanes containing a di(4-phenylene)terephthalate unit. The compounds of both series possess high transition temperatures and narrow mesomorphic ranges.     

Mesogenic behaviour of two series of orthopalladated polar inline derivatives and their organic ligands (II)

Abstract

One series of 4-n-octyl-N-(4-X-benzylidene)anilines and two series of polar orthopalladated complexes derived from these of type Pd₂(μ-Y)₂ p-X-C₆H₃-CH = N-C₆H₄-C₈H_{17 2}; X: -H, -F, -Cl, -Br, -NO₂, -CN, -CH₃, -OCH₃, -CF₃, -COOCH₃, -OCOCH₃ and -OCOQH₅; Y: -OAc and -Cl; have been synthesized and their mesogenic properties studied. In the polar Schiff bases used as organic ligands, the polar end group determines both the presence of the mesophase and the type of mesophase exhibited. In the complexes, however, it is the central structure of the molecule that practically always determines mesogenic behaviour. No acetato-bridged complex is mesogenic. All the chloro-bridged complexes, however, show mesogenic behaviour. All these compounds show smectic A mesophases with the exception of the CN compound, which only exhibits a nematic mesophase.     

Evidence of re-entrant ferroelectric ordering in an achiral AFLC: a detailed study by spontaneous polarization

A winged achiral antiferroelectric liquid crystalline compound, 1,3-phenylene bis-[phenylene1-(biphenyldicarboxylato)-3-(4-n-tetradecyloxybenzoyl)biphenyldicarboxylate] (PBPBTB), having 1,3-phenylene [4-biphenyldicarboxylate-(4-n-tetradecyloxy benzoate)] units as wings, has been synthesized. Its mesogenic properties were characterized by thermal microscopy, differential scanning calorimetry, response time and spontaneous polarization measurements, and dielectric studies, suggesting the presence of new achiral phases. An interesting enantiotropic cyclic sequence among ferro- and antiferro-electric ordering was confirmed by the polarizing current profiles. The occurrence of re-entrant ferroelectric phenomena in the present compound was confirmed by detailed spontaneous polarization and preliminary dielectric studies.     

Synthesis,characterisation and liquid crystalline properties of some Schiff base and cinnamate central linkages involving 1,3,5-trisubstituted pyrazolone ring system and their Cu(II) complexes

Two new mesogenic homologous series, each containing 1,3,5-trisubstituted pyrazolone derivatives, 4-n-alkoxyphenyl and Schiff base–cinnamate central linkages, have been synthesised to give 4-[(5-hydroxy-3-methyl-1-phenyl-4,5-dihydro-1H-pyrazol-4-yl) methyleneamino] phenyl 3-(4-n-alkoxyphenyl)acrylate [Series-A] and 4-[(5-hydroxy-3-methyl-1-p-tolyl-4,5-dihydro-1H-pyrazol-4-yl)methyleneamino] phenyl 3-(4-n-alkoxyphenyl)acrylate [Series-B] and their Cu(II) complexes have also been synthesised. These compounds were characterised by elemental analysis, Fourier transform infrared (FT-IR), proton nuclear magnetic resonance (¹H NMR), carbon-13 NMR (¹³C NMR) and ultraviolet (UV)-visible and mass spectral studies. Their mesomorphic behaviour was studied by polarising optical microscope (POM) with a heating stage. POM data were compared with differential scanning calorimetry thermograms. In Series-A and -B, all compounds exhibit mesomorphism. Series-A compounds exhibit an enantiotropic nematic mesophase except propyl derivative, while a smectic A (SmA) mesophase is observed from the heptyl derivative and persists up to the last member of the homologous series. n-Heptyloxy derivative is monotropic for SmA phase. Series-B compounds also exhibit the enantiotropic nematic mesophase, while the SmA mesophase is observed from the heptyl derivative and persists up to the last member of the homologous series. n-Dodecyloxy derivative exhibits monotropic SmA and nematic mesophases. The mesomorphic properties of both series are compared with each other and the other structurally related compounds. The study reveals that cinnamate linkage containing liquid crystals have higher thermal stability compared to structurally related series containing chalcone linkage. In case of complex series, only one compound from each series gives nematic mesophase.     

Studies on thermotropic main chain liquid crystalline segmented polyurethanes I. Synthesis and properties of polyurethanes from high aspect ratio mesogenic diol as chain extender

Thermotropic main chain liquid crystalline polyurethanes were prepared from 4-{[4-(6-hydroxyhexyloxy)phenylimino]methyl}benzoic acid 4-{[4-(6-hydroxyhexyloxy)phenylimino]methyl}phenyl ester (mesogenic diol) and 1,6-hexamethylene di-isocyanate. The effects of partial replacement of the mesogenic diol by 20-50 mol% of poly(tetramethylene oxide)glycol (PTMG) of varying molecular mass (M _n =650, 1000, 2000) on the liquid crystalline properties were studied. Structural characterization was carried out by FTIR spectroscopy and the molecular mass distribution was determined by GPC. Differential scanning calorimetry and hot stage polarizing optical microscopy were used to study the mesomorphic properties. It was observed that the partial replacement of the mesogenic diol by PTMG of varying molecular masses influenced the phase transitions and the occurrence of mesophase textures. When the molecular mass of PTMG was enhanced, a higher content of mesogenic agent was needed to obtain liquid crystalline properties.     

Phase behaviour of hydrogen-bonded liquid crystalline complexes of alkoxycinnamic acids with 4,4'-bipyridine

The hydrogen-bonded liquid crystalline complexes of 4-n-alkoxycinnamic acids (nCNA: n=4-8, 10, 12, 16, 18, where n is the number of carbons in the alkoxy chain) with 4,4'-bipyridine (BPy) have been prepared and characterized. The existence of smectic C, smectic A, and nematic mesophases of these complexes was demonstrated by a combination of polarized optical microscopy and X-ray diffraction (XRD). In this H-bonded mesogenic structure, nonmesogenic BPy functions as the core unit of the mesogen through the H-bond, as confirmed by infrared spectroscopy and XRD. A general comparison of nCNABPy with the benzoic acid analogues (nOBA)_2-BPy, showed that the elongated nCNABPy mesogen behaves as a rod unit and increases the transition temperature. Smectic phases in nCNAs (5≤ n≤ 12) were induced on complexation with BPy. The favouring of smectic phases in these complexes is believed to originate from the increment of polarity of the mesogen by intermolecular H-bonding. With increasing chain length of the nCNABPy complexes the smectic C phase becomes stabilized, like conventional rod-coil molecules.     

Coumarin based emissive rod shaped new schiff base mesogens and their zinc(II) complexes: synthesis,photophysical, mesomorphism,gelation and DFT studies

New homologous series of coumarin Schiff base derived from 6-aminocoumarin and their zinc(II) complexes have been synthesised. The spectroscopic characterisations, photophysical properties, phase transition temperature, characterisation of phase and gelation behaviour are reported. The ligand is non-mesogenic at lower 4-n-alkoxy chain length (n = 4) and mesogenic for longer chains (n > 4). For small chains (n = 5, 7, 8), ligand displays monotropic nematic or nematic-smectic A phase sequences, whereas longer homologues (n = 12, 14, 16 and 18) display only enantiotropic smectic A phase. The ligands and their Zn(II) complexes are fluorescent in nature. Interestingly, ligands exhibit gelation property only in polar solvents, whereas Zn(II) complexes discourage gelation. The effect of 4-n-alkoxy chain length on the gelation properties was also discussed. Density functional theory calculations show broad agreement with observed molecular conformation, dipole moment, molecular orbitals and polarisability of the coumarin Schiff base molecules and their Zn(II) complexes.     

Liquid crystalline properties of unsegmented and segmented polyurethanes synthesised from high aspect ratio mesogenic diols

A series of novel tetrad high aspect ratio mesogenic diol monomers 4-{[4-(n-hydroxyalkoxy)-phenylimino]-methyl}-benzoic acid 4-{[4-(n-hydroxyalkoxy)-phenylimino]-methyl}-phenyl ester were prepared with varying alkoxy spacer length (n=2,4,6,8,10) by reacting 4-formylbenzoic acid 4-formylphenyl ester and 4-(n-hydroxyalkoxy) anilines. Two series of thermotropic main chain liquid crystalline unsegmented polyurethanes (PUs) were obtained by the polyaddition of the mesogenic diols with hexamethylene diisocyanate (HMDI) and methylene bis(cyclohexylisocyanate) (H₁₂MDI) in dimethylformamide respectively. The effect of the incorporation of a third component namely polyol on the liquid crystalline properties of the polyurethanes was also studied. Linear segmented PUs were synthesised by a two-step block copolymerisation method. The PUs synthesised were based on six spacer mesogenic diol chain extender, soft segments poly(tetramethylene oxide)glycol (PTMG) (M_n= 650,1000,2000) and polycaprolactone diol (PCL) (M_n=530,1250,2000) of varying molecular weights and different diisocyanates including HMDI, H₁₂MDI and methylene bis(phenylene isocyanate) (MDI). Structural elucidation was carried out by elemental analysis, fourier transform infra red (FT-IR), nuclear magnetic resonance (¹H NMR and ¹³C NMR) spectroscopy. Inherent viscosity of the unsegmented polymers measured in methanesulphonic acid at 26°C was in the range of 0.13 - 0.65 dL/g while the molecular weights and molecular weight distribution of the segmented polyruethanes was determined using gel permeation chromatography (GPC). Mesomorphic properties were studied by differential scanning calorimetry (DSC) and hot stage polarising optical microscopy and the thermal stability was determined by thermogravimetric(TG)analysis. The monomeric diols and the polyurethanes exhibited nematic texture and good mesophase stability. It was observed that the partial replacement of the mesogenic diol by the polyol of varying molecular weights influenced the phase transitions and the occurrence of mesophase textures. The phase transition temperatures of the investigated polyurethanes showed dependence on the chain length of the soft segment and on the content of the mesogen moiety. A higher content of mesogenic moiety was needed to obtain liquid crystalline property when the soft segment length was increased as observed in the case of PTMG. Grained and threaded textures were observed depending on the molecular weight of the soft segment, the mesogen content and the diisocyanate. The stress-strain analyses showed that the polymers bused on high molecular weight PTMG soft segment have elastomeric property while the PCL based PUs displayed no elastomeric property.     

Synthesis,characterisation and mesomorphic properties of ester containing aroylhydrazones and their nickel(II) complexes

A new series of mesogenic aroylhydrazone-based ligands, N-[4-(4′-alkoxy)benzoyloxybenzylidene]-N′-[4″-alkoxybenzoyl]hydrazine with either the same or different peripheral alkyl chains, and nickel(II) complexes of some of them have been synthesised. They were characterised by elemental analyses, Fourier transform infrared, proton and carbon nuclear magnetic resonance and ultraviolet-visible spectroscopy. The mesomorphic properties of these compounds were investigated by differential scanning calorimetry and polarising optical microscopy. All the aroylhydrazones, except those with no lateral chains on either end of the molecule and where m?=?n?=?14, 16, exhibit a monotropic or enantiotropic smectic C mesophase, which are almost insensitive to the peripheral alkoxy chain length. The square planar nickel(II) complexes of the ligands show only an isotropic phase at higher temperature (>175°C) and no mesogenic nature is observed. Density functional theory calculations have been performed using the GAUSSIAN-03 program at the Becke, three-parameter, Lee–Yang–Parr level to obtain the stable electronic structure of the ligand.     

Synthesis and characterisation of asymmetrical mesogenic materials based on 2,5-disubstituted-1,3,4-oxadiazole

New mesogenic homologous series bearing 1,3,4-oxadiazole ring with a nitro terminal group, 4-(5-(4-nitrophenyl)-1,3,4-oxadiazol-2-yl)phenyl 4-((4-methoxybenzylidene)amino)benzoate (G₁–G₁₁), were synthesised. Their chemical structures are identified by fourier transform infrared spectroscopy (FT-IR), proton nuclear magnetic resonance (¹H-NMR) and elemental analysis. The liquid crystalline properties of the series G_n and their precursory F_n were screened by differential scanning calorimetry and optical polarising microscopy (OPM). The compounds of the series G_n were screened by thermogravimetric analysis to observe their thermal stability. The target compounds (G_n) in this study, were displayed different liquid crystalline mesophase, the first two homologous (G₁ and G₂) did not show any liquid crystalline behaviour, the homologous (G₃–G₁₀) which have an alkoxy terminal group (n = 3–10) exhibited nematic phase, whilst the last derivative of the series (G₁₁), n = 12, displayed SmA phase. The mesomorphic properties of these derivatives were affected by the presence of the nitro group at the end of the molecules which was classified as a strong polar group. Also, the role of alkoxy terminal chain and the bent heterocyclic ring (1,3,4-oxadiazole) in the liquid crystalline properties of these molecules were debated.     

Synthesis and study of mesogenic compounds having a methylene ketone (-CH2-CO-) linking group

Abstract

Recently we have reported isoflavone derivatives as potential mesogens [1]. During the synthesis of isoflavone derivatives, 2,4-dihydroxyphenyl benzyl ketone was synthesized as an intermediate. Nguyen Huu Tinh et al. [2] have reported the effect of the influence of the central linkage, such as ethylene, methylene ketone and ketone on the mesogenic compounds. Vora et al. [3] have also reported a mesogenic homologous series with terminal and lateral phenolic groups. To understand the effect of hydrogen bonding originating between methylene ketone and free lateral hydroxy groups, ortho to the methylene ketone group, on mesogenicity, the present homologous series of 2-hydroxy, 4(4′-n-alkoxybenzoyloxy)phenyl benzyl ketone was synthesized. The synthesized compounds were characterized by elemental analysis and spectroscopic techniques. The first six homologues of the present series are non-mesogenic and mesomorphism appears from the heptyl derivative onwards. The present series shows a monotropic smectic A phase except for the last member (octadecyloxy) which exhibits an enantiotropic smectic A mesophase. The transition temperatures are also identified using DSC. The fluorescent studies of some of the compounds of the present series are under investigation.     

Synthesis and mesomorphic properties of chiral liquid crystal dimers derived from azobenzene and substituted naphthol

Symmetrical liquid crystal dimers bis{2-alkyl-(S)-(+)-2-(6-[4-4′-decyloxyphenylazo)-benzoyloxy]-2-naphthyl)propinate} have conveniently been designed, synthesised and their mesomorphic properties were investigated. These dimers possess two identical mesogenic units with each of them attached to the terminal end of a flexible spacer (–C _n H_2n ; where n = 6–10). The respective mesogenic unit was made up from a naphthyl ring attached to the alkyloxylated azobenzene via the ester (COO–) bond. The chiral moiety attached to the 6-position of the naphthyl ring possesses a terminal carboxylic group COO– which linked up the mesogenic unit and the spacer. The thermal and optical properties for the ultimate compounds at different temperature were studied explicitly with the aids of differential scanning calorimetry and polarising optical microscopy. All dimers exhibit unambiguously the monotropic nematic and smectic A phases. The homeotropic alignment of the molecules within the anisotropic region was further confirmed through the application of homogeneously treated cell.     

Metastable complexes of some <Emphasis Type="Italic">d</Emphasis>- and <Emphasis Type="Italic">f</Emphasis>-block metals with mesogenic cyanobiphenyls

Formation of metastable complexes with different metal to mesogenic ligand ratio (M/L = 1/2 and 1/1) has been shown by IR–, UV–Vis, ESR-spectroscopic techniques for low temperature co-condensation of some d- and f-block transition metals (Ag, Cu, Eu, Sm) and mesogenic derivatives of cyanobiphenyls. The Quantum chemistry calculations have been carried out to study equilibrium structures of complexes. Biligand complex models with one and two metal atoms and antiparallel disposition of two ligand molecules are considered. Relative spectral shifts and relative thermal stability of complexes are discussed.     

Low-temperature biligand complexes of europium and samarium with mesogenic alkylcyanobiphenyls

For low-temperature cocondensates of europium and samarium (M) with a mesogenic ligand 4-pentyl-4-cyanobiphenyl (L), IR and UV spectroscopy studies have revealed the formation of two ML complexes (M/L = 1:2 and 1:1). Model calculations have been carried out in terms of density functional theory using the B3LYP exchange correlation potential. Biligand structures with an antiparallel arrangement of two ligand molecules including one and two metal atoms, respectively, are suggested. The values of the spectral shifts and the relative thermal stability of the complexes are discussed.Original Russian Text Copyright © 2004 by A. V. Vlasov, T. I. Shabatina, S. V. Konyukhov, A. Yu. Ermilov, A. V. Nemukhin, and G. B. SergeevTranslated from Zhurnal Strukturnoi Khimii, Vol. 45, No. 3, pp. 406–411, May–June, 2004.     

Azomesogens containing a β-chloroethyl terminal chain: synthesis and characterisation

In this paper, we present the synthesis and characterisation of two new mesogenic homologous series, β-chloroethyl 4-(4′-n-alkoxyphenylazo) benzoates (I) and the β-chloroethyl [4-(4′-n-alkoxybenzoyloxy)phenylazo]-4”-benzoates (II), containing a terminal β-chloro ethyl chain. Series I was synthesised by alkylation of β-chloroethyl 4-(4′-hydroxy phenylazo) benzoate with an appropriate alkyl halide, whereas series II was synthesised by esterification of β-chloroethyl 4-(4′-hydroxyphenylazo) benzoate with an appropriate 4-n-alkoxybenzoic acid. The molecular structures of these new compounds of both the series were characterised by combination of element analysis and a standard spectroscopic method. The mesomorphic behaviour was studied mainly by use of a polarised microscope and, in some cases, differential scanning calorimeter as well. In series I, all nine members synthesised exhibited only an enantiotropic smectic A mesophase. In series II, all 12 homologues exhibited an enantiotropic nematic mesophase; a smectic A phase appeared in the n-octyloxy derivative as an enantiotropic phase and persisted through to the n-hexadecyloxy member. The mesomorphic properties of both series were compared with each other and also with the properties of other structurally related series to evaluate the effects of the β-chloroethyl tail on mesomorphism.     

Effect of a lateral methyl group on azo-mesogens containing the naphthalene moiety

Two mesogenic homologous series, 2-[4-(4-n-alkoxybenzoyloxy)-2-methylphenylazo]-naphthalenes (I) and 2-[4-(4-n-alkoxybenzoyloxy)-3-methylphenylazo]naphthalenes (II) with a lateral methyl group have been synthesized. Both series are purely nematogenic. The mesomorphic properties of both series are compared with each other and also with the properties of other structurally related series to evaluate the effect of the lateral methyl group on mesomorphism. The chiral nematic (N*) mesophase was induced in the system by doping with a derivative of naturally occurring chiral menthol.     

Properties of liquid-crystalline copper(II) complexes and their binary mixtures

Abstract

Eight new copper compounds with mesogenic properties from the series of the bis{1-[4-trans-(4-alkylcyclohexy1)phenyl]-alkylpropane-1,3-dionato} copper(II) complexes have been prepared. The thermal behaviour of these compounds was investigated by means of polarizing microscopy and differential scanning calorimetry (D.S.C.) measurements. The mesophase, which could be found in most of them, is of the monotropic nematic type. This has been confirmed by miscibility experiments. The physical data of a binary mixture with an enantiotropic mesophase are also presented. In addition the crystal structures of two of the compounds are reported.