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.     

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.     

A new procedure for determining copper in igneous rock and alloys

The influence of cationic surfactants, cetylpyridinium chloride (CPC), cetylpyridinium bromide (CPB), and cetyltrimethylammonium bromide (CTMAB), on the complexation of copper(II) with thenoyl-(2-oxopropyl)-N-(2-sulfo-4-nitro-5-oxyphenyl) azomethine (R) has been investigated. It has been found that monoligand compounds are formed at pH 4, while at pH 3 the formation of mixed-ligand compounds is observed. The detection limit for copper decreases and the stability constants of the complexes increase in the row Cu-R-CPC > Cu-R-CPB > Cu-R-CTMAB, with AN increase in the stability of the associates (Rh-CPC > R-CPB > R-CTMAB) in the complexation reaction. The ratio of components in monoligand (1: 1) and mixed-ligand (1: 1: 1) compounds has been determined. The limits of obedience to the Beer law have been found. A procedure has been developed for the photometric determination of copper in igneous rock and alloys.     

Effect of orientation of lateral fluorine atom on the mesophase behaviour of azo/ester molecules with terminal naphthyl group

ABSTRACT

Two homologous series of the three-ring 4?-(4"-alkoxy-2"-(or 3")fluoro phenylazo) benzoates terminated with 2-(or 1-) naphthyl groups (In_d&e or IIn_d&e), respectively, were prepared and their mesophase behaviour investigated via differential scanning calorimetry, whereas the type of the mesophase identified by polarised light microscopy. Molecular structures of compounds prepared were first characterised via infrared, ¹H-NMR and elemental analyses. Transition temperatures were correlated with the alkoxy chain length (n) that varies between 6, 8, 10, 12, 14 and 16 carbons.

Comparative studies were made to investigate the effect of including the lateral fluorine atom, and its orientation, into the previously investigated fluorine-free analogues, namely, 2-(or 1-) naphthyl 4?-(4"-alkoxyphenylazo) benzoates (In_a and IIn_a). The study was extended to investigate the effect of replacing the methyl group in the previously prepared 2"- and 3"-methyl analogues (In_b&c or IIn_b&c) with the fluorine atoms on their mesophase behaviour.     

Synthesis and mesomorphic properties of 2-(4′-alkoxybiphenyl-4-yl)-1H-benzimidazole derivatives

Three series of 2-(4′-alkoxybiphenyl-4-yl)-1H-benzimidazole derivatives (nM-x), which possessed 5-nitrobenzimidazole (nM-N series), benzimidazole (nM-H series) or 5-methylbenzimidazole (nM-M series) units at the end of the molecule, were synthesised and characterised by infrared, ¹H- and ¹³C-nuclear magnetic resonance spectra, electrospray ionisation-mass spectrometry and elemental analysis. Their phase transition behaviour was investigated by differential scanning calorimetry, polarising optical microscopy and X-ray diffraction. All the compounds exhibited enantiotropic smectic mesophases with wide temperature domains for a carbon number in the alkoxy chain from 6 to 16, where the mesophase ranges were 14–91°C and 17–99°C during heating and cooling processes for the nM-N compounds, 7–25°C and 8–49°C for the nM-H compounds and 48–81°C and 52–85°C for the nM-M compounds, respectively. The effect of the length of alkoxy chain on mesomorphic properties was discussed. The nM-N and nM-M exhibited a much wider mesophase range whether during heating or cooling process than the corresponding nM-H series, especially for the longer terminal chain (n > 8), which indicated that the substituent in the benzimidazole moiety was helpful in increasing the mesophase stability.     

Effect of lateral bromo substituent on the phase behavior of four-ring azo/ester/azo liquid crystalline materials

ABSTRACT

In order to study the influence of lateral Br substitution on mesophase behaviour, five homologous series of 4-substituted phenylazo phenyl 4?-(3?-bromo-4?-alkoxyphenylazo) benzoates (In_a–e) have been synthesised. Within each homologous series, the alkoxy group varies from 6 to 16 carbons, while other terminal group substituents, X, are CH₃O, CH₃, H, Br and NO₂ groups; the mesophase behaviour of these series is compared with previously prepared laterally neat analogues, 4-substituted phenylazo phenyl 4?-(4?-alkoxyphenylazo) benzoates (IIn_a–e) and laterally methyl analogues, 4-substituted phenylazo phenyl 4?-(3?-methyl-4?-alkoxyphenylazo) benzoates (IIIn_a–e). Similar to lateral methyl analogues, the present series, lateral Br substitution showed that, independent of the polarity of the substituent X or the alkoxy-chain length, the nematic phase is predominant with relatively high stability and broad temperature ranges. The mesophase stability varies between 204.0°C and 335.0°C for the nematic phase and 169.6°C and 281.0°C for the SmA phase. Their total mesophase temperature ranges vary between 87.2°C and 201.4°C. All compounds were found to be thermally stable within the mesophase temperature range, except the lower homologue of the nitro and Br substituted derivatives. The obtained results are discussed in terms of molecular polarisability.     

Effect of orientation of extra fused benzene ring and lateral methyl substituent on the mesophase behaviour of three-ring azo/ester molecules

ABSTRACT

Two homologous series of the three-ring azo/ester compounds 2-(or1-) naphthyl 4?-(4?’-alkoxy phenylazo) benzoates (In_a and IIn_a) were synthesised. A lateral methyl group was introduced in different positions of the alkoxy phenyl moiety, in position-2 to give series In_b and IIn_b and in position-3 to give series In_c and IIn_c. Molecular structures were characterised via elemental analyses, infrared and ¹H-NMR. Their mesophase characteristics were investigated by differential scanning calorimetry (DSC) and their phases identified via polarised light microscopy (PLM). Transition temperatures were correlated with the alkoxy-chain length (n) that varies between 6, 8, 10, 12, 14, and 16 carbons. Comparative studies were first made to investigate the effect of including the extra fused benzene ring, and its orientation, into the previously investigated three-ring compounds, 4-phenyl 4?-(4′′-alkoxyphenylazo) benzoates (IIIn_a). Investigation of the mesophase behaviour was extended to cover the effect of introducing the lateral methyl group and its position. The comparison between the present six series and their corresponding phenyl analogues IIIn_a,b,c, indicated that the 2-naphthyl analogues, In_a,b,c, exhibit the highest mesophase stability. Whereas, the steric effect of the protruded naphthalene group destabilises all mesophases and appear only monotropically. The results were discussed in terms of polarisability effect.     

Oximato-bridged copper(II) compounds: syntheses,molecular structures,magnetic, thermal and spectroscopic properties

Reaction of the Schiff base, 1-(4-methylimidazol-5-yl) phenylhydrazonopropane-2-one oxime (LH), with copper(II) perchlorate hexahydrate and copper(II) nitrate trihydrate in a 1 : 1 M proportion in methanol affords [Cu₂L₂(H₂O)(ClO₄)](ClO₄) (1) and [Cu₂L₂(H₂O)₂](NO₃)₂] (2) in moderate yields. Both 1 and 2 have been characterized by elemental analysis, ESI-MS, FT-IR, UV–vis absorption spectroscopy, EPR, electric conductivity, and magnetic susceptibility measurements. The X-ray crystal structures of 1·CH₃COCH₃ and 2 have been determined. Both compounds are dinuclear copper(II) complexes, with each copper μ₂-bridged by two oxime ligands in a μ₂-η¹,η² fashion. Variable temperature magnetic studies on 1 and 2 show that both compounds are dominated by an antiferromagnetic coupling through the oxime bridges.     

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 4?-(4?-alkoxy phenylazo) benzoates (In_a–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 4?-(4?-alkoxy phenylazo) benzoates (In_i–k).     

New azobenzene-based natural fatty acid liquid crystals with low melting point: synthesis,DFT calculations and binary mixtures

ABSTRACT

Three new groups of azobenzene liquid crystals named,4-[2-(4-substituted phenyl)diazenyl]phenyl hexdecanoate, 4-[2-(4-substituted phenyl)diazenyl]phenyl octadeca-9-enoate, and 4-[2-(4-substituted phenyl)diazenyl]phenyl octadeca-9,12-dienoate were prepared from naturally occurring fatty acids (palmitic, oleic and linoleic acids). All groups were investigated for their mesophase formation and thermal stability of pure compounds and their binary mixtures by differential scanning calorimetry (DSC), polarised light microscopy (PLM) and thermogravemetric analyses (TGA). Each group contains two compounds that differ from each other by the polar substituent X (CH₃O and Cl) with different number (n) of carbons in the fatty alkyl chains. Molecular structures of the prepared compounds were confirmed via FT-IR, ¹H NMR, C¹³ NMR and elemental analysis. Mesomorphic and thermal properties were investigated. Smectic A phase is the mesophase observed in all of the compounds prepared and their binary mixtures with low melting temperatures. Moreover, DFT calculations were discussed for the prepared compounds. The results revealed that the alkyl chain of the carboxylate part does not significantly affect on the energy difference of the FMOs as well as the thermodynamic parameters. However, the high electronegative Cl substituent has significant effect on the energy difference of the FMOs and decreases the dipole moments of the prepared compounds.     

The effect of terminal substituents on crystal structure,mesophase behaviour and optical property of azo-ester linked materials

A series of azo-ester linked mesogen containing liquid crystalline acrylate compounds C1-C6 having different terminal groups (–F, –Cl, –Br, –OCH₃, –OC₂H₅ and –OC₃H₇) were successfully synthesised and characterised. The chemical structure, purity, thermal stability, mesophase behaviour and optical property of the synthesised compounds were investigated by different instrumental techniques. X-ray crystal structure showed that compounds C1, C4 and C5 exhibited more stable E configuration with two bulky group in the opposite side of the N=N double bond motifs. The fluoro-substituted derivative (C1) is connected by the R¹₂(5) type of C–H…O hydrogen bond motifs whereas the molecules of C4, and C5 are connected to each other by means cyclic R²₂(8) type of C–H…O hydrogen bond motifs. Thermogravimetric study revealed that the investigated compounds exhibited excellent thermal stability. All the compounds showed enantiotropic liquid crystal (LC) phase behaviour and the mesophase formation was greatly influenced by the terminal substituents. Alkoxy (–OCH₃, –OC₂H₅ and –OC₃H₇) substituted compounds exhibited greater mesophase stability than those of halogen (–F, –Cl and –Br) terminated derivatives. UV-vis spectroscopic study revealed that the investigated compounds exhibited a broad absorption band around 300–420 nm with absorption maximum (λ_max) of nearly 370 nm.     

Schiff base/ester liquid crystals with different lateral substituents: mesophase behaviour and DFT calculations

Four new groups of 4-((2?-substitutedphenylimino)methyl)phenyl-4”-alkoxy benzoates, In_a-d, of Schiff base ester liquid crystals, were prepared and investigated for their mesophase formation and stability. Each group constitutes four homologous series that differ from each other by the lateral attached polar group X in the ortho position for the imine mesogen at terminal benzene ring that alternatively changed from F, Br, NO2 and lateral benzene ring. Within each homologous series, the number (n) of carbons in the alkoxy chain varies between 6, 8, 10 and 12. Molecular structures of the prepared compounds were confirmed via elemental analysis, FT-IR, and ¹H NMR spectroscopy. Mesomorphic properties were investigated by differential scanning calorimetry (DSC) and the phase identified by polarised light microscopy (PLM). A comparative study was made between the investigated compounds and their previously prepared laterally neat, 4-((4?-phenylimino)methyl)phenyl-4”-alkoxy benzoates (IIn); the result revealed that all lateral substituents not only decrease the melting temperature but also the mesophase stability and shown only nematic phase. Density functional theory (DFT) calculations for new lateral derivatives were discussed.     

Mesophase stability of new Schiff base ester liquid crystals with different polar substituents

Four new groups of Schiff base ester liquid crystal compounds, 4-((4?-substituted phenylimino) methyl)phenyl–4″-alkoxybenzoates, In_a–d, were prepared and investigated for their mesophase formation and stability. Each group constitutes four homologous series that differ from each other by the polar substituent X (CH₃O, CH₃, H, and Cl). Within each homologous series, the number (n) of carbons in the alkoxy chain varies between 6, 8, 10, and 12. Molecular structures of the prepared compounds were confirmed via FT-IR, ¹H NMR, mass spectroscopy, and elemental analysis. The mesomorphic properties were investigated by differential scanning calorimetry and polarised light microscopy. Comparative studies between the present series and previously investigated 4-(4-substituted phenylazo)phenyl 4″-alkoxybenzoates revealed that the phenylimino mesogenic core increases the mesophase stability rather than the azo analogues.     

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.     

Mesogenic quinazolone derivatives: synthesis and characterisation

Two new mesogenic homologous series of quinazolone derivatives have been synthesised by condensation of 4-n-alkoxybenzoyloxy benzaldehyde (for series I) / 4-n-alkoxy-3-methoxybenzoyloxy benzaldehyde (for series II) with 3-amino-2-methyl quinazolone in alcohol. The synthesised compounds are characterised by a combination of elemental analysis and standard spectroscopic methods. In series I, all the synthesised members exhibit the nematic mesophase. An enantiotropic smectic A phase is observed from the n-decyloxy derivative onward to the last homologue synthesised. Methoxy to n-propyloxy derivatives of series II are non-mesogenic, whereas the rest of the members exhibit a monotropic nematic mesophase. The mesomorphic properties of the present series I and II are compared with each other and with the other structurally related mesogenic homologous series to evaluate the effect of lateral methoxy substituent and quinazolone moiety on mesomorphism.     

Preparation and mesomorphic properties of 1-methyl-1H-benzimidazole-based compounds

A series of 1-methyl-1H-benzimidazole-based compounds, 2-(4?-alkoxy-1,1?-biphenyl-4-yl)-1-methyl- 1H-1,3-benzimidazole derivatives (nPPMx-M) with terminal hydrogen, methyl and nitro moieties (coded as nPPMH-M, nPPMM-M and nPPMN-M, respectively), were prepared and their structures were characterised. The compounds display enantiotropic smectic mesophases for hydrogen and methyl terminated compounds (nPPMH-M and nPPMM-M), and enantiotropic nematic mesophases for nitro terminated compounds (nPPMN-M) with short alkoxy chain below than 10 carbon atoms, where the mesophase ranges are 24–72°C and 74–104°C on heating and cooling processes for nPPMH-M, 90–119°C and 110–135°C for nPPMM-M, and 102–129°C and 113–207°C for nPPMN-M, respectively. It is noted that the compounds nPPMx-M exhibit much lower melting points and much wider mesophase range both in heating and cooling than non-1-methyl substituted analogs, which are ascribed to the disruption of hydrogen bonding among the molecules caused by methyl substitution at 1-position of benzimidazole. Meanwhile, among the compounds nPPMx-M, much wider mesophase ranges are obtained for nPPMM-M and nPPMN-M, indicating a much high mesophase stability for the compounds bearing terminal moiety (CH₃ and NO₂).     

Structures and magnetic properties of two new heterospin complexes involving nitroxide radicals and oxamido-bridged copper(II)

Two new binuclear copper(II) complexes containing four spin carriers with pyridyl-substituted nitroxide radicals have been synthesized and characterized structurally and magnetically. These complexes are formulated as [Cu₂(oxap)(IM4py)₂](ClO₄)₂ (1) and [Cu₂(oxap)(NIT4py)₂](ClO₄)₂ (2), respectively, in which oxap stands for N,N′-bis(2-aminopropyl). IM4py stands for 2-(4′-pyridyl)-4,4,5,5-tetramethylimidazoline-1-oxyl and NIT4py for 2-(4′-pyridyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide. The structures of the complexes consist of centro-symmetric trans oxamido-bridged copper(II) binuclear units and nitroxide radicals. In 1 and 2 the copper atoms are in a distorted square plane and radicals (IM4py and NIT4py) coordinate to copper via nitrogen atoms from pyridine rings. Magnetic analysis indicates that 1 and 2 exhibit strong metal-metal antiferromagnetic coupling through oxamido-bridged and antiferromagnetic exchange interactions between copper(II) ion and radicals, respectively. The magnetic behaviors are discussed with reference to their crystal structures.     

Synthesis and liquid crystalline investigation of chiral 6-alkoxy-2-naphathoic acid derivatives

A two new series of materials with a chiral fragment derived from ((S)-(─)-2-methyl-1-butanol and 6-alkoxy-2-naphathoic acid as the molecular core was synthesised and investigated. All the homologues exhibited enantiotropic mesomorphism. Chiral smectic C (SmC*), smectic A (SmA) and chiral nematic (N*) phases were observed in different homologues. All the compounds were characterised by spectroscopic and elemental analysis. Thermal investigations and mesophase characterisations for all the compounds were carried out by the combination of DSC and POM analysis. The effects of the central linkage and various terminal normal alkyl chains with its structurally related compounds have been discussed.     

Mesogenic cinnamates with a substituted ethyl terminal chain*

Two new mesogenic homologous series of liquid crystalline cinnamates with substituted ethyl tails, β‐methoxyethyl [4‐(4′‐n‐alkoxycinnamoyloxy)benzoates (I) and β‐chloroethyl [4‐(4′‐n‐alkoxycinnamoyloxy)benzoates (II), have been synthesized and characterized by a combination of elemental analysis and standard spectroscopic methods. In series I, lower‐chain members exhibit nematic mesophase, middle members exhibit enantiotropic nematic as well as smectic A (SmA) mesophases, whereas higher members exhibit only an enantiotropic SmA mesophase. In series II, methoxy to n‐butyloxy derivatives exhibit a monotropic nematic mesophase. The SmA mesophase commences from n‐propyloxy derivative as monotropic and persists up to the last member synthesized. The mesomorphic properties of present series were compared with each other and with a structurally related mesogenic homologous series to evaluate the effects of substituted ethyl tail and cinnamoyloxy central linkage on mesomorphism.     

The effect of terminal epoxy modification on the mesomorphic and thermal stability of biphenyl ester liquid crystals

ABSTRACT

A series of biphenyl ester compounds with alkenyl, alkyl, oxirane, and 1,3-dioxolane as the terminal groups have been synthesised for investigating the mesomorphic and thermal stability. Based on the same carbon skeleton, the allyl-terminated compound V1OLC has no mesophase, while the oxirane-terminated compound POLC not only has wider multiple smectic mesophase compared with the propyl-terminated compound 3OLC but also exhibits the best thermal stability. However, when the terminal groups change from oxirane to 1,3-dioxolane, EOLC shows neither mesophase nor the good thermal stability. In addition, with the extension of the terminal chains, the butyl-terminated compound 4OLC gives the widest smectic mesophase. These imply that the mesomorphic and thermal stability of these biphenyl ester compounds are dependent on the suitable terminal chain lengths and epoxy sizes. Meanwhile, Density Functional Theory (DFT) calculations were conducted to assist in analysing the experimental results.