Banana-shaped mesogens: effect of lateral substituents on seven-ring esters containing a biphenyl moiety
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The synthesis and characterization of five homologous series of symmetrical compounds composed of banana-shaped molecules containing a biphenyl moiety are reported. All these compounds are non-Schiff's bases and are esters. The effects of lateral substituents such as fluoro, methyl and ethyl in the side arms of these molecules are examined. These substituents have a strong influence in reducing the clearing temperatures. Banana phases such as B1, B2 and B6 were observed in the above series of compounds. The mesophases were characterized by a combination of polarizing optical microscopy, differential scanning calorimetry, X-ray diffraction and electro-optic studies.Keywords:
Moiety
Biphenyl
Homologous series
Side chain
AbstractA novel liquid crystal (LC) homologous series of 12 azoesters was synthesized and evaluated, and nine members of the series exhibited enantiotropically or monotropically nematogenic LC behavior. Smectogenic character is totally absent. The methoxy, tetradecyloxy, and hexadecyloxy homologues are non-liquid crystals (NLC). Textures of nematic phase are threaded, or schlieren. The solid–isotropic/nematic and N-I or vice versa transition curves behave in normal manner. The N-I transition curve exhibits an odd-even effect. The average thermal stability for nematic is 113.25°C. Mesomorphic phase length ranges from 21 to 35°C. The textures of nematic mesophase and transition temperatures were determined by an optical polarizing microscope equipped with a heating stage. Analytical and spectral data confirm the molecular structures of homologues. The LC behavior of the present novel series is compared with a structurally similar known series. The present series is predominantly nematogenic with the absence of smectic property, and is of a middle-ordered melting type.Keywords: Azoesterliquid crystalsmonotropysmecticnematic AcknowledgmentsThe authors are thankful to the head and teaching staff of applied chemistry of Faculty of Technology and Engineering, M.S. University, Vadodara, for their valuable cooperation in the work. Authors are also thankful to CSMCRI, Bhavnagar, for the analysis of samples.
Homologous series
Polarized light microscopy
Thermotropic crystal
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Abstract The temperature dependences of surface tension, γ=f ≠ (t), are experimentally studied and discussed for homologous series of liquid crystalline 4-alkyl-4′-cyano biphenyls, 4-alkyl-4′-cyanophenylbenzoates, 4-alkyloxy-4′-cyanophenylbenzoates and also for several nematic liquid crystals of other chemical classes. The surface energy anisotropy of 5CB is measured at fixed temperature.
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Biaxial nematic
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Abstract The general rule that addition of a non-mesogenic solute causes a sharp decrease in the nematic-isotropic transition temperature (TN→ I) of a nematic solvent is not obeyed when the solute and solvent can enter into a donor-acceptor interaction. Addition of 4-aminobiphenyl to the nematic liquid crystal 4-cyano-4′-pentylbiphenyl (nematic range ∼ 25–35°) leads to an increase in TN→ I and a decrease in the crystal-nematic transition temperature. The maximum nematic range (21–38°) is achieved at ∼ 7 mole % solute.
Mesogen
Atmospheric temperature range
Biaxial nematic
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Abstract Two homologous series of coumarin derivatives have been synthesized and mesomorphic behavior of their members has been studied. In case of Series I, mesomorphism does not begin to appear until the butyl homolog, which is monotropic nematic. The remaining members of the series exhibit both nematic and smectic or only smectic properties. In case of Series II, all the homologs, except the first seven, exhibit only a smectic phase. In both the series, plots of S-N or I transition temperatures versus the number of carbon atoms in the alkoxy chain show an ascending tendency.
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Carbon chain
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A novel monomeric homologous series of α,β-ethylene derivatives was synthesized and studied with a view to understanding and establishing the relation between molecular structure and liquid crystal properties. The series consists of 12 novel compounds. The methoxy to propyloxy derivatives are not liquid crystals, the butyloxy homologue is monotropic nematic, the pentyloxy homologue is monotropic smectic and enantiotropic nematic, and the rest of the homologues (C6–C16) are enantiotropically smectic in addition to nematic. Transition temperatures and texture were determined by an optical polarizing microscope equipped with a heating stage, and show an odd–even effect for nematic–isotropic and smectic–nematic transition curves. Analytical and spectral data confirm the molecular structures. The average smectic and nematic thermal stabilities are 84.9°C and 94.15°C, respectively. The liquid crystal properties of present series are compared with the structurally similar known series.
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Mesogen
Biaxial nematic
Polarized light microscopy
Texture (cosmology)
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AbstractA novel ester homologous series of 4-[4’-n-alkoxy cinnamoyloxy] benzyl benzoates has been synthesized. The series consists of 12 homologues. Liquid crystal properties commence from the sixth member to the last member of the series with the exhibition of an enantiotropic nematic phase without the exhibition of any smectogenic mesophase. The remaining homologues do not exhibit liquid crystal behavior. The texture of the nematic phase is of the threaded or Schlieren type. The solid-nematic or isotropic transition curve adopts a zigzag path and the nematic-isotropic transition curve steeply rises and then falls in the phase diagram and behaves in normal manner. An odd–even effect is absent in the nematic-isotropic transition curve with an alteration of transition temperatures. The average thermal stability for the nematic mesophase is 153.1°C, and the nematogenic temperature ranges vary from 12°C to 50°C. Analytical data confirm the molecular structures of the homologues. The Liquid Crystal properties and transition temperatures were observed through an optical polarizing microscope, equipped with a heating stage. The mesomorphic characteristics of the novel ester series are compared with other, known and structurally similar series. The novel series is predominantly nematogenic with the absence of any smectogenic character, with relatively short mesophase temperature ranges and of the middle ordered melting type. Keywords: Liquid crystalsmesomorphismmonotropynematicsmectic AcknowledgmentAuthors acknowledge thanks to the Green Circle Inc. Lab for research facilities services as and when needed. Authors also thank DR. N.N.Vyas, DR Vipul Patel, and DR M.L.Chauhan for their valuable helping hand and microscopic facility. Thanks are due to the Sophisticated Instrumentation Center for Applied Research and Testing, Vallabh Vidhyanagar, Gujarat for analytical services.
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Polarized light microscopy
Terphenyl
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Abstract An approximate solution is derived for the structure of a twist wall between two regions of opposite 180° twist in a nematic liquid crystal film. The result is used to show that a twist wall is unstable unless the elastic constants of the nematic are such that K22≤ ½(K11 + K33). Thus the observation of such walls in nematic liquid crystals is evidence of this elastic anisotropy. Experimental evidence is given for the validity of the approximate solution obtained.
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Abstract Miscibility phase diagrams of mixtures of side-on side chain liquid crystalline polymers (s-SCLCP) and low molar mass liquid crystals (E48 and E44) have been established by means of polarized optical microscopy and light scattering. E48 and E44 are cyanobiphenyl-based eutectic nematic liquid crystal (LC) mixtures with nematic-isotropic transition temperatures of 93 and 105 C, respectively. The phase diagram of the s-SCLCP/E48 system reveals the coexistence of an isotropic nematic region and a single nematic phase in order of descending temperature. The single nematic phase suggests that the pair is miscible in the nematic region. On the other hand, the s-SCLCP/E44 mixture shows liquid liquid and nematic nematic coexistence phases, suggestive of the immiscibility character of the pair. These nematic phase diagrams of the s-SCLCP/E48 and s-SCLCP/E44 have been analysed in the context of the combined Flory-Huggins (FH) free energy for isotropic mixing and the Maier-Saupe (MS) free energy for nematic ordering of the mesogens. This combined FH/MS theory is capable of predicting the observed nematic phase diagrams consisting of liquid liquid, liquid nematic, nematic nematic, and the pure nematic regions. The change of colour accompanying the appearance and disappearance of the inversion walls may be attributed to the temperature dependence of birefringence.
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Abstract The crucial role of the smectic A-nematic transitional order for the formation of the smectic A, B and G phases from an electrically deformed nematic phase of the liquid crystal 4-n-hexyloxy-benzylidene-4′-n-butylaniline (6O.4) with a typical smectic A-nematic first order transition and the formation of the smectic A and B phases from an electrically deformed nematic phase of the liquid crystal (4-n-butyloxy-benzylidene-4′-n-octylaniline (40.8) with a smectic A-nematic second order transition has been demonstrated. The nematic phase was deformed by an AC voltage of 2U,th 5U th and 10U th, where U th is the threshold voltage which causes the appearance of the Fréedericksz transition in the homeotropic nematic layer. The smectic textures have been observed on free cooling of the nematic phase or after the use of an oven. The smectic A phase of the liquid crystal 60.4 was observed with the formation of a clear smectic A-nematic phase boundary while the smectic A phase of the liquid crystal 40.8 has been formed from intermediate pretransitional stripes, observed by Cladis and Torza [1]. The homeotropic anchoring of the direction was crucial for the formation of the smectic phases of the liquid crystal 40.8 but not significant for the liquid crystal 60.4.
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Biaxial nematic
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Abstract Most mesogens formed by banana-shaped molecules exhibit liquid-like smectic phases. Here we present the synthesis and properties of homologous series of derivatives of resorcinol and 2,6-disubstituted pyridine. One of these classes of bent-core molecules displays the nematic phase.
Biaxial nematic
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