Synthesis of new mesogenic compounds having the isoflavone core group

Two new series of calamitic liquid crystals containing the isoflavone moiety within the central core have been prepared and their liquid crystalline properties studied. The compounds exhibit typical nematic, smectic A and C mesophases. The influence of the linking group between a terminal alkyl chain and the central core has been proven to determine the variety of mesomorphism displayed by the compounds.     

Novel chiral liquid crystals based on amides and azo compounds derived from 2-amino-1,3,4-thiadiazoles: synthesis and mesomorphic properties

Novel chiral amides (Ia-Ie, II) and azo compounds (III, IV) with a 1,3,4-thiadiazole unit in the rigid core were synthesized and their liquid crystalline properties investigated by polarizing optical microscopy and differential scanning calorimetry. The amides Ia-Ie contain a chiral alkoxy chain derived from (R)-2-octanol and an achiral chain varying from 6 to 10 carbon atoms at the end of the rigid core. In amide II one of the terminal group is a chiral alkoxy chain derived from (S)-isoleucine and the other terminal substituent is an achiral n-decyloxy chain. Azo compounds III and IV contain an achiral n-decyloxy chain and a chiral alkoxy chain derived from (R)-2-octanol and (S)-isoleucine, respectively, at the end of the rigid core. The first homologue in the series of amides (Ia) exhibits enantiotropic smectic X (SmX)-chiral nematic (N*) dimorphism and the homologues Ib-Ie display enantiotropic SmX-chiral smectic C (SmC*)-N* mesomorphism. Amide II displays an enantiotropic smectic A phase. The azo compounds III and IV do not show smectic order and only an enantiotropic N* phase was observed. Thus, the mesomorphic behaviour depends on the nature of the central linkage and on the nature of the chiral alkoxy chain.     

λ-Shaped azomesogens with polar chloro- and nitro-substituents

A new homologous series of λ-shaped mesogenic azo esters with polar chloro- and nitro- substituents has been synthesised by attaching a rigid 2-chloro-4-nitrophenylazo group to a resorcinol moiety by a central azo linkage. Both phenolic hydroxyl groups are esterified by 4-n-alkoxybenzoyl groups. All the compounds synthesised have been characterised using a combination of elemental analysis and standard spectroscopic methods. The mesomorphic properties of the compounds have been determined by polarising optical microscopy and differential scanning calorimetry. The lower members of the series are non-mesogenic, the middle members exhibit a nematic mesophase, and higher members exhibit a smectic A mesophase. The effect of polar chloro-, nitro-, and long lateral aromatic substituents, on mesomorphism is discussed.     

Liquid crystalline compounds with V-shaped molecular structures: synthesis and characterization of new azo compounds

The synthesis and mesomorphic properties of a series of 1,2-phenylene bis[4-(4-alkyloxyphenylazo)benzoates] are reported. The mesophases exhibited by these bent-shaped azo compounds are identified as nematic, smectic A and crystal E phases. All these compounds have fairly low transition temperatures, and so are suitable for physical studies. It has been concluded that the -CH N- linkage can be more conducive to mesomorphism compared with the -N N- linkage.     

Synthesis,Characterization and Investigation of Side Chain Length and/or Substituents Effect on the Liquid Crystal Properties of New Mesogens

New substituted and unsubstituted phenol based mesogene series having an azo central linkage was synthesized by fixing phenol as rigid core unit with aromatic amine. The terminal –OH group was esterified successively by long alkyl chain acid chloride of variable length (n=2, 6, 11, 15, 17). All 25 synthesized compounds exhibit mesomorphism. The effect of side chain length and substituents on the stability of liquid crystals was studied. The study reveals that nitro substituent destabilizes nematic and smectic phases more than floro substituent. Furthermore, the transition temperature decreases as the length of side chain increases.     

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.     

Novel bent-shaped liquid crystalline compounds II. Synthesis and properties of the 1,3-bis4-[4-(4-alkyloxybenzoyloxy)benzylidene]aminophenoxypropan-2-ols

A series of new symmetric dimer compounds was synthesized, constaining 2-hydroxy-1,3-dioxypropylene as the central linkage and terminal alkyl chains with different lengths. The chemical structures of the liquid crystal dimers (2ES-n) were examined by FTIR and ¹H NMR spectroscopy. Their mesomorphism, thermodynamic properties and optical textures were investigated by differential scanning calorimetry, polarizing optical microscope and X-ray diffraction. For homologues with terminal propyloxy and butyloxy chains, no liquid crystalline phase was observed. Homologues with pentyloxy and hexyloxy terminal chains showed nematic phases, while those with heptyloxy, octyloxy, nonyloxy and decyloxy terminal chains displayed nematic phases and smectic phases. The results confirmed that the liquid crystalline phase changes from nematic to smectic as the terminal chain length increases.     

Synthesis and study of 4-(4'-n-alkoxybenzoyloxybenzoyl)-4'-n-butoxyanilides

Thirteen compounds with ester and amide linkages were synthesized and their mesogenic properties evaluated. Methyl to n-propyl derivatives exhibit nematic phases, n-butyl to n-decyl derivatives exhibit smectic and nematic mesophases, whereas n-dodecyl to n-octadecyl derivatives exhibit only smectic phases. All the smectic homologues exhibit smectic C phases. Middle members of the homologous series exhibit polymorphism of smectic mesophase. A plot of transition temperatures versus number of carbon atoms in the alkoxy chain reveals an odd-even effect for nematic-isotropic transition temperatures. Nematic-isotropic and smectic-cholesteric thermal stabilities of the prepared compounds (series I) are higher compared to those of previously reported compounds, series A, B and C. The results indicate that a simple reversal of a central linkage has a dramatic effect on the appearance of smectic mesophase in a homologous series. The structures of the synthesized compounds were characterized using elemental analysis, thin-layer chromatography and spectral data.     

Optical and thermal properties of unsymmetrical liquid crystalline compounds based on isoxazole

The thermal and optical properties of two series of unsymmetrical liquid crystalline compounds based on an isoxazole ring are described. Of these materials, 3–7 and 8–12 displayed strong absorption at 285 nm and a weak blue fluorescence in solution at around 377 nm, even with the presence of a high conjugated core. The fluorescence quantum yields observed varied from low to moderate (Φ _F ?=?1–62%), with large Stokes shifts (60–178 nm). All compounds exhibited liquid crystalline behaviour with a wide mesomorphism temperature range and characteristic phases of calamitic compounds, among them smectic A (SmA), smectic C (SmC) and nematic (N) phases. Their phases were characterised using polarising optical microscopy and differential scanning calorimetry. In addition, with X-ray diffraction experiments, layer spacing of 33.3–40.0 Å were observed for the smectic phases.     

Synthesis and study of 4‐(4′‐n‐alkoxybenzoyloxybenzoyl)‐4′′‐n‐butoxyanilides

Thirteen compounds with ester and amide linkages were synthesized and their mesogenic properties evaluated. Methyl to n‐propyl derivatives exhibit nematic phases, n‐butyl to n‐decyl derivatives exhibit smectic and nematic mesophases, whereas n‐dodecyl to n‐octadecyl derivatives exhibit only smectic phases. All the smectic homologues exhibit smectic C phases. Middle members of the homologous series exhibit polymorphism of smectic mesophase. A plot of transition temperatures versus number of carbon atoms in the alkoxy chain reveals an odd–even effect for nematic–isotropic transition temperatures. Nematic–isotropic and smectic–cholesteric thermal stabilities of the prepared compounds (series I) are higher compared to those of previously reported compounds, series A, B and C. The results indicate that a simple reversal of a central linkage has a dramatic effect on the appearance of smectic mesophase in a homologous series. The structures of the synthesized compounds were characterized using elemental analysis, thin‐layer chromatography and spectral data.     

4-Octylphenylazo-4′-phenyl alkanoates – homologous series of azomesogens with extremely rich liquid-crystalline polymorphism

This paper presents synthesis and liquid-crystalline properties of full homologues series (from acetate to arachidate) of 4-octylphenylazo-4′-phenyl alkanoates. All of the 19 synthesised compounds are liquid crystals with extremely rich mesomorphism. The ester chain length strongly influences mesogenic behaviour of presented materials. In some compounds, up to four liquid-crystalline phases have been observed. There were six different mesophases detected: nematic, smectic C, smectic F, smectic I, J and G. Moreover, some homologues display two crystalline forms. This latter phenomenon does not depend on the ester chain length. Identification of such complicated phase sequences was made based on four methods: polarised light microscopy, thermo-optical analysis, differential scanning calorimetry and X-ray measurements.     

Nematic and smectic mesophases in a new series of Cu(II) organometallic complexes

The synthesis and the phase behaviour of a homologous series of copper, bis[N-[[4-[4-(alkoxy)benzoyloxy],2-hydroxyphenyl]methylene]-methanamino] complexes is reported. They all exhibit thermotropic mesomorphism. The thermal stability range of the mesophase decreases slightly with increasing length of the alkoxy terminals. With the onset of smectic mesomorphism, for alkoxy groups containing ten carbon atoms, the stability interval of the nematic phase decreases progressively so that the compound containing 14 carbon atoms in the alkoxy terminal chains exhibits only smectic mesomorphism. Optical texture analysis suggests the smectic C nature of the phase in all cases. The enthalpies for the liquid crystal-isotropic transition have been measured and they are comparatively low. Remarkably low values have also been measured for the melting enthalpies of the smectogenic members of the series. These are associated with solid phase polymorphism which is discussed briefly.     

Constitutional bis(N-salicylideneaniline)s as new class of mesogens: synthesis and thermal properties

Twelve new constitutional bis(N-salicylideneaniline)s (BSANs) belonging to three different series have been prepared and characterised by the two-fold reaction of alkoxyanilines with 2,3-dihydroxyterephthalaldehyde, 4,6-dihydroxyisophthalaldehyde and 2,5-dihydroxyterephthalaldehyde. Their thermal behaviour and liquid crystallinity has been established with the help of polarising optical microscope, differential scanning calorimeter (DSC) and powder X-ray diffraction (XRD). Our study reveals this behaviour as determined by the nature of central core and the number of alkoxy tails. For example, the three series of compounds prepared are either non-mesomorphic or stabilised calamitic and discotic mesophases, such as nematic/smectic C and columnar (Col) phases. These materials represent the first examples of mesogenic BSANs exhibiting mesomorphism.     

Self-assembly of azo molecules to mesogenic phasmid-like materials through inter-molecular hydrogen bonding

A series of acid-functionalised new azo compounds was synthesised and characterised. The constituent molecules self-organise to form dimers through inter-molecular hydrogen bonding, resulting in phasmid-like compounds. This was once considered to be a promising molecular architecture to form biaxial nematic phases. The mesomorphic properties of these new azo compounds were studied using polarising optical microscopy, differential scanning calorimetry and X-ray diffraction. Investigations revealed that these compounds form nematic and columnar mesophases. A few more compounds were synthesised by replacing the??N=N- linkage in these compounds with??CH=N- and??COO- to study the effect of different linkages on the mesomorphic properties in such molecular systems. All were found to be liquid crystalline. The compounds with a??N=N- linkage are more conducive to mesomorphism and are thermally very stable. The effect of number of alkoxy chains on the mesomorphic properties of this system was also studied. To the best of our knowledge, at present, only a handful of phasmid-like mesogenic compounds, formed by the intermolecular hydrogen bonding, are known.     

Synthesis,characterisation and liquid crystalline properties of some Schiff base-ester central linkage involving 2, 6- disubstituted naphthalene ring system

Four new mesogenic homologous series, each containing a 6-alkoxy 2-naphthoic acid and Schiff base-ester as central linkage, have been synthesised by esterification of 4-{[(4-hydroxyphenyl) imino] methyl} phenyl 4-propoxy benzoate, 4-{[(4-hydroxyphenyl) imino] methyl} phenyl 4- (pentyloxy) benzoate, 4-{[(4-hydroxyphenyl)imino]methyl}-2-methoxyphenyl 4- nitrobenzoate and 4-{[(4-hydroxyphenyl)imino]methyl}-2-methoxyphenyl 4- chlorobenzoate with different 6-alkoxy 2-naphthoic acid to give Series-A, -B, -C and -D, respectively. These compounds were characterised by elemental analysis, Fourier transform infrared, ¹H nuclear magnetic resonance, ultraviolet-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 a enantiotropic nematic mesophase, while a smectic A mesophase is observed from the butoxy derivative and persists up to the last member of the homologou series. Series-B compounds also exhibit the enantiotropic nematic mesophase, while the smectic A mesophase is observed from the ethoxy derivative and persists up to the last member of the homologou series. The mesomorphic properties of both series are compared with each other and the other structurally related Series-C and –D compounds. In Series-C and -D all compounds exhibit the only nematic mesophase; no smectic mesophase is observed even for higher members of the homologous.

The aim of the research was to synthesise and characterise novel liquid crystalline compounds containing 2,6-disubstituted naphthalene and to study their mesomorphic properties.     

Polar 2-alkoxyethoxy-substituted nematic liquid crystals

The synthesis is reported of a series of polar nematic liquid crystals incorporating an alkoxyalkoxy chain attached in a terminal position to a molecular core consisting of two aromatic rings. The dependence of the mesomorphism and phase transition temperatures on the nature of this terminal chain was studied. The shape anisotropy of the core is increased by the presence of an additional 1,4-disubstituted phenyl unit in a number of p-terphenyls. A number of highly polar esters with a terminal methoxyethoxy chain have been prepared as dopants to lower the threshold voltage of LCDs. The presence of the methoxyethoxy chain leads to an increase in the molecular dipole moment, the dielectric anisotropy and the dielectric constant perpendicular to the molecular long axis. Several compounds with a four-unit diether central linkage were also prepared.     

New fluorescent mesogens with a chalcone central linkage

Mesogens with a chalcone central linkage are rare. It is believed that the chalcone linkage is not conducive to mesomorphism. In the present study two homologous series were synthesized having the chalcone as a central linkage. 4-n-alkoxy-4'-hydroxy chalcones do not exhibit mesomorphism, however, higher members of 4-n-alkoxy-4'(4'-n-octyloxybenzoyl) chalcones, exhibit mesomorphism. The fluorescent behaviour of the chalcones is evaluated. All the compounds are characterized by standard methods.     

The influence of lateral apolar substituents on the mesomorphic behaviour of tetracatenar liquid crystals

Several series of new tetracatenar mesogens consisting of a five-ring aromatic core and bearing one or more apolar lateral substituents in the central benzene ring of the molecule have been synthesized and their mesomorphism is characterized by polarization microscopy, differential scanning calorimetry, and X-ray diffraction methods. Introduction of one, two, or four methyl groups into these tetracatenar mesogens destabilized columnar organization typical of the long-chain homologs, but did not suppress smectic C and nematic phases. Introduction of larger substituents did, however, suppress lamellar organization (C₁₅H₃₁) or mesomorphism (tert-butyl) totally.     

Synthesis and characterization of two isomeric liquid crystal series with reactive double bonds

Two series of potentially cross-linkable liquid crystal materials derived from p-phenylenebisacrylic (series I, n(P.FB.P), n = 2-10) and p-hydroxycinnamic acid (series II, n(HC.T.HC), n = 2-10) have been synthesized and their thermal and mesomorphic properties studied. All these compounds show enantiotropic mesomorphism over a wide range of temperatures. Compounds with short terminal chains are nematic and when the terminal chain length is increased they show smectic polymorphism-smectic A and C. Most of the compounds are thermally stable over their mesophase ranges.     

Synthesis and liquid crystal properties of copper(II) and palladium(II) chelates with new ferrocene-containing enaminoketones

Heterometallic liquid crystals are of special interest because of the possibility to combine optical, magnetic and electric properties of different metal ions in one mesogenic molecule. In order to investigate new heteropolynuclear mesogenic systems, a series of β-aminovinylketone ligands derived from acetyl ferrocene have been synthesized. Subsequently Cu(II) and Pd(II) ions were incorporated into the enaminoketone chelate core. The obtained ligands and complexes were characterized by element analysis, ¹H NMR, IR and UV–Vis spectroscopies. According to thermal polarizing microscopy and DSC studies, the ligands and Cu(II) complexes exhibit disordered soft crystal phases upon cooling from the isotropic liquid state. The Pd(II) complexes showed monotropic smectic C mesomorphism. The metal centres in the synthesized heteropolynuclear mesogens are in close vicinity to each other, which is of considerable interest from the viewpoint of the potential electron-transfer interactions between a ferrocene core and the central ions.