Mesomorphism dependence on molecular rigidity and flexibility

A novel homologous series of liquid crystalline properties is synthesized and studied with a view to understand the effect of molecular structure on its thermotropic properties. Novel homologous series consisted of thirteen homologs. All the homologs are enantiotropically smectogenic with absence of nematic property even in the monotropic condition. Textures of the homologs as observed through an optical hot stage polarizing microscopy. The mesophase temperature range vary minimum from 6.0°C to a maximum 37.0°C at the methyloxy and propyloxy derivatives of a series respectively with its thermal stability (Sm–I) 127.0°C. Transition curves of a phase diagram behaved in normal manner. Odd–even effect is observed for Sm–I transition curve.     

Synthesis and Quantum-chemical Study of Liquid-crystal Derivatives of Thiazole

New liquid-crystall derivatives of thiazole with smectic mesomorphism over the range 5-85°C have been synthesized. Data on the spatial structure of the compounds synthesized have been obtained by quantum-chemical calculations. The effect of geometric anisotropy of the molecules of substituted thiazoles on their mesomorphic properties has been investigated.     

3-烷氧基-6-（4-甲氧羰基苯基）哒嗪的合成及介晶性研究

3，6-二氯哒嗪和醇在相转移催化剂(C_4H_9)_4NBr和浓碱作用下，合成3-氯- 6-烷氧基哒嗪，在三苯基膦钯的催化下，用3-氯-6-烷氧基哒嗪与对甲氧羰基苯基 硼酸偶联，并以较好产率合成了八种中心桥连基为哒嗪环，含有苯环、酯基、不同 长度烷氧基的哒嗪衍生物，并通过差示扫描量热法（DSC）对其介晶性进行了表征 ，同时发现其中七种都具有介晶性。研究表明，末端链长度对相变温度和清亮点温 度均有影响。     

Star-shaped discotic compounds with tetrazole and oxadiazole fragments

ABSTRACT

Two series of star-shaped discotic compounds (A and B) were studied to establish the relationship between their molecular structure and mesogenity. Series A included 19 three-arm compounds with known mesomorphism. Series B consisted of 132 new compounds with unknown mesomorphism: pyromellitic and cyanuric acid derivatives, 5,5′-azo-bis-isophthalic and 4,4′-azodiphthalic acids and triphenylene derivatives. The columnar mesomorphism prediction data for both series were obtained using the original program СМР ChemCard. The prediction data for series A are in good agreement with the experimental results and the reliability of the prediction was estimated to be 89.5%. The same method was applied for series B. The prediction results were approved by the synthesis of individual representatives of series B. A good correlation of the prediction with the experimental data was revealed.     

Emissive ‘zinc(II)-salphen’ core: building block for columnar liquid crystals

A series of half-discoid [N₂O₂]-donor tetradentate alkoxy substituted salicylaldimine ligands, [N,N′-di- (4-n-alkoxysalicylidene)-4-Cl-l,2-diamino-benzene] (L; n?=?12, 14, 16 and 18) have been prepared. The reaction of the ‘salphen’-type Schiff base ligand with Zn(OAc)₂.4H₂O afforded a series of mononuclear zinc(II) complexes. The ligands and the corresponding zinc(II) complexes were characterised by elemental analysis, Fourier transform infrared, proton nuclear magnetic resonance and ultraviolet-visible spectroscopy. Although the ligands are non-mesogenic, columnar mesomorphism is induced upon complexation with the metal. The p2gg symmetry of the rectangular columnar phase is confirmed by variable temperature powder X-ray diffraction study. Two ‘half-disc’-shaped molecules with four alkoxy legs are presumed to self-assemble via a dimeric interaction filling the space. In contrast to the ligands, the zinc(II) complexes all exhibited moderately intense green emission at room temperature both in solution and in the solid state. Density functional theory calculation, carried out using a DMol3 program, revealed a distorted square planar geometry for the complexes. The mesomorphic and photoluminescence property of the zinc complexes are collated as a function of spacer substituent, as well as alkoxy carbon chain length.     

Novel supramolecular columnar liquid crystals based on thiosemicarbazides

Novel liquid crystal materials based on 3,4-di-n-alkoxybenzoylthiosemicarbazides (3a–h, n = 5–10, 12, 14) were synthesised. The mesomorphic properties of these compounds were characterised and studied by differential scanning calorimetry, polarising optical microscopy and X-ray diffraction. Compound 3a did not show mesomorphic properties; 3b shows a monotropic hexagonal columnar (Col_h) phase. Compounds 3c–h display an enantiotropic Col_h phase. The mesomorphic properties were found to be dependent on the length of alkoxy side chains. In N,N-dimethylformamide solution, all the compounds displayed a room temperature emission with λ_max at 361–332 nm. A thermogravimetric analysis also was performed.     

The effect of locations of triple bond at terphenyl skeleton on the properties of isothiocyanate liquid crystals

Three series of new tolanyl benzene isothiocyanate liquid crystals A, B and C were synthesised with lateral fluorine substituent at different positions and 3,5-difluoro terminal groups. Series D and compound E4 with carbon–carbon triple bond connected with the isothiocyanated benzene were also prepared as reference. Their structures were confirmed using infrared spectrometry, nuclear magnetic resonance and mass spectrometry. The mesomorphic properties, birefringence, dielectric anisotropy and miscibility of these compounds were investigated. Series A exhibits higher clearing points than that of the corresponding compounds D. Series B displays the lowest melting points, the broadest nematic phase temperature range and no smectic phase with increase of the carbon number of alkyl chain. Lateral fluorine in the position of Y (series C) results in an increase of smectic phase. The birefringence (~0.454–0.490) of series A is almost the same as that of the corresponding reference compounds D, while series B shows a decrease of Δn about 0.05 compared with compounds D. For comparison, mixtures formulated by A and B exhibit higher clearing points and better low temperature stability than those of the mixtures based compounds D in the same fraction.