H. N. Shreenivasa Murthy

Banana-shaped mesogens: effect of lateral substituents on seven-ring esters containing a biphenyl moiety

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-Schiffs 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.

A polar biaxial smectic A phase in new unsymmetrical compounds composed of bent-core molecules

The synthesis and liquid crystalline properties of several new compounds unsymmetrically substituted about two different central phenyl rings are reported. All the compounds contain a strongly polar terminal cyano/nitro substituent. Some of the nitro-substituted compounds derived from 3-hydroxybenzoic acid show a transition from the partial bilayer uniaxial smectic A (SmAd) phase to a polar partial bilayer biaxial smectic A (SmAdPA) phase. The analogous cyano-substituted derivatives exhibit only a SmAd phase. However, compounds containing a 4-cyanobiphenyl moiety in the terminal position and derived from 1,3-dihydroxybenzene show the SmAd – SmAdPA transition. The mesophases were characterized using polarizing optical microscopy, differential scanning calorimetry, X-ray diffraction studies, conoscopic examination and miscibility studies.The synthesis and liquid crystalline properties of several new compounds unsymmetrically substituted about two different central phenyl rings are reported. All the compounds contain a strongly polar terminal cyano/nitro substituent. Some of the nitro-substituted compounds derived from 3-hydroxybenzoic acid show a transition from the partial bilayer uniaxial smectic A (SmAd) phase to a polar partial bilayer biaxial smectic A (SmAdPA) phase. The analogous cyano-substituted derivatives exhibit only a SmAd phase. However, compounds containing a 4-cyanobiphenyl moiety in the terminal position and derived from 1,3-dihydroxybenzene show the SmAd – SmAdPA transition. The mesophases were characterized using polarizing optical microscopy, differential scanning calorimetry, X-ray diffraction studies, conoscopic examination and miscibility studies.

Mesogenic dimers composed of bent-core molecules with flexible alkylene spacer

The synthesis and characterization of six symmetrical mesogenic dimers composed of bent-core molecules containing alkylene spacers are reported. The mesophase was characterized by polarizing optical microscopy, differential scanning calorimetry, X-ray diffraction and electric field experiments. The X-ray diffraction studies revealed a columnar structure with an oblique lattice for the mesophase. The electric field experiments indicated a ferroelectric behaviour for the mesophase. On the basis of obtained experimental data, a possible structural model for the mesophase has been proposed.

Effect of lateral substituents on the mesophases formed by some achiral banana-shaped molecules

Several compounds composed of banana-shaped molecules and exhibiting mesophases are reported. The effect of different lateral substituents on the type of mesophase formed is examined and a comparison made with unsubstituted compounds. The mesophases have been characterized using techniques such as polarizing optical microscopy, differential scanning calorimetry, and X-ray diffraction. The B2 phase shows antiferroelectric switching behaviour.

Banana-shaped mesogens: a new homologous series of compounds exhibiting the B7 mesophase

The synthesis and characterization of a new homologous series of compounds, the 2-cyano-1,3-phenylene bis[4-(4-n-alkoxyphenyliminomethyl)benzoates] derived from 2-cyanoresorcinol is reported. All the compounds are enantiotropic mesogens and exhibit the fascinating B7 mesophase. The characterization of the mesophase was performed using polarizing optical microscopy, differential scanning calorimetry, X-ray diffraction and electro-optical studies.The synthesis and characterization of a new homologous series of compounds, the 2-cyano-1,3-phenylene bis[4-(4-n-alkoxyphenyliminomethyl)benzoates] derived from 2-cyanoresorcinol is reported. All the compounds are enantiotropic mesogens and exhibit the fascinating B7 mesophase. The characterization of the mesophase was performed using polarizing optical microscopy, differential scanning calorimetry, X-ray diffraction and electro-optical studies.

Synthesis and mesomorphic properties of unsymmetrical bent-core compounds containing 1,3-phenylene or 2,7-naphthylene as the central unit

The synthesis and mesomorphic properties of four new homologous series of unsymmetrical bent-core compounds with 1,3-phenylene or 2,7-naphthylene as the central unit are reported. These compounds contain an α-methylcinnamoyloxy bridging group in one of the arms. Three types of mesophases, namely, N, B1 and B2 are observed in these compounds. The rarely observed transitions N to B1 and N to B2 have been observed in some of the compounds derived from 2,7-dihydroxynaphthalene. In one of the compounds derived from resorcinol, textural features of both B1 and B2 phases appear simultaneously on cooling the isotropic phase. The mesophases were characterized using conventional techniques.The synthesis and mesomorphic properties of four new homologous series of unsymmetrical bent-core compounds with 1,3-phenylene or 2,7-naphthylene as the central unit are reported. These compounds contain an α-methylcinnamoyloxy bridging group in one of the arms. Three types of mesophases, namely, N, B1 and B2 are observed in these compounds. The rarely observed transitions N to B1 and N to B2 have been observed in some of the compounds derived from 2,7-dihydroxynaphthalene. In one of the compounds derived from resorcinol, textural features of both B1 and B2 phases appear simultaneously on cooling the isotropic phase. The mesophases were characterized using conventional techniques.

Influence of a fluorine substituent on the mesomorphic properties of unsymmetrical five-ring bent-core compounds

The synthesis and mesomorphic properties of unsymmetrical five-ring bent-core compounds containing a fluorine substituent in one of the arms are reported. A comparison of the properties with the symmetrical compounds having two fluorine substituents indicates that the position of this substituent has an influence on the nature of the mesophase observed. Evidence for the occurrence of a transition from the rectangular columnar (B1) phase to an antiferroelectric lamellar (B2) phase, which is rather rare, is provided. The mesophases have been characterized using polarized light microscopy, differential scanning calorimetry, X-ray diffraction and electro-optical studies.

Observation of a transition from non-switchable B7 mesophase to an antiferroelectric sub-phase in strongly polar bent-core compounds

The synthesis and characterization of two new homologous series of five-ring Schiffs base esters exhibiting the non-switchable B7 mesophase are reported. These compounds have been derived from either 2-nitro- or 2-cyanoresorcinol. Interestingly, three higher homologues of the nitro-substituted compounds undergo a transition from the non-switchable B7 mesophase to an antiferroelectric sub-phase (B7AF1), which is the first example of such a transition. In addition to comparing the mesomorphic behaviour of the two series of compounds, the effect of reversing the azomethine linkage group in these series of compounds has also been examined. The mesophases have been characterized by conventional techniques.

Ferroelectric and antiferroelectric switching behaviour in new unsymmetrical bent-core compounds derived from 3-hydroxybenzoic acid

Herein we report the synthesis and characterization of several achiral bent-core unsymmetrical compounds exhibiting mesomorphic properties. The lower homologues in two series of compounds show a columnar phase with a rectangular lattice whereas the middle homologues exhibit a novel columnar phase with an oblique lattice. Interestingly, three of the higher homologues of the laterally unsubstituted compounds exhibit a smectic phase with ferroelectric switching characteristics and the analogous fluoro-substituted compounds show a smectic phase that is composed of antiferroelectric conglomerates.

Observation of filamentary growth patterns at the isotropic–SmCPA phase transition in new unsymmetrical compounds composed of bent-core molecules

The synthesis and mesomorphic properties of several compounds composed of bent-core molecules, unsymmetrically substituted about the central phenyl ring, are discussed. These compounds contain substituents such as fluoro, chloro and trifluoromethyl at the terminal position of one of the arms of the bent-core molecules. Many of the compounds containing a chloro terminal substituent show filamentary growth patterns at the transition from isotropic to polar antiferroelectric smectic C phase. The liquid crystalline phase exhibited by these compounds has been characterized using a combination of polarizing optical microscopy, differential scanning calorimetry, X-ray diffraction and electro-optical studies.