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.     

Columnar and smectic liquid crystals based on crown ethers

Unsymmetrical benzo[15]crown-5 ethers 5 with one lateral ortho-terphenyl unit bearing alkoxy side chains of varying chain lengths (C5-C14) were prepared from 3,4-dialkoxyphenylbromides 2. Complexation with metal salts MX (M = Na, Cs) afforded the corresponding derivatives MX5. The uncomplexed crown ethers 5 h and 5 i, with dodecyloxy and tetradecyloxy side chains, respectively, exhibit liquid crystalline properties. In the series of complexed crown ethers, liquid crystal properties appeared as early as NaI5 f with C9H19 side chains. Whereas the uncomplexed 5 h,i form smectic mesophases, the complexed NaI5 g and NaI5 h exhibit textures typical of columnar mesophases. These results were supported by X-ray diffraction measurements (WAXS, SAXS), which revealed smectic (5 h,i), rectangular columnar (NaI5 g), and hexagonal columnar (NaI5 h) mesophases. As the liquid crystalline phase might retain packing features of the solid-state structure, single-crystal X-ray analyses were also performed for some of the uncomplexed and complexed crown ether derivatives. The complex NaI(3)5 a displays a sandwich-type structure, with the crown ether cores mutually antiperiplanar and maintaining an almost perfect crown conformation. In contrast, non-mesogenic uncomplexed crown ether 5 b displays a layer-type ordering in the solid phase.     

Columnar liquid crystalline benzenetrisamides with pendant 1,3,4-oxadiazole groups

Novel liquid crystal materials based on 1,3,5-benzenetrisamide derivatives with three pendant 2-phenyl-5-(mono-, di-, and/or tri-n-alkoxyphenyl)-1,3,4-oxadiazole arms (Ia–c, IIa–c) were prepared. The mesomorphic properties of these compounds were characterised and studied by differential scanning calorimetry, polarising optical microscopy and X-ray diffraction. The formation of a columnar mesophase was found to be dependent on the number of alkoxy side chains. The compounds Ib and IIb, with a total of six alkoxy chains, and compounds Ic and IIc, with nine alkoxy chains, exhibited an enantiotropic hexagonal columnar (Col_h ) phase with high isotropisation temperatures; however, compounds Ia and IIa with a total of three alkoxy chains formed a crystalline phase. Compounds IIb and c were room temperature liquid crystals.     

Star-shaped molecules as functional materials based on 1,3,5-benzenetriesters with pendant 1,3,4-thiadiazole groups: liquid crystals,optical, solvatofluorochromic and electrochemical properties

New molecular structures consisting of a C₃ star-shaped 1,3,5-benzene unit as a central core, and three pendant 2-phenyl-5-(di-, and/or tri-n-alkoxyphenyl)-1,3,4-thiadiazole arms, containing ester connecting groups, variable number and positions of linear alkoxy chains (2an, 2b10 and 2c10) were synthesised. The mesomorphic properties were studied by differential scanning calorimetry, polarised optical microscopy and X-ray diffraction. Compounds bearing nine peripheral n-decyloxy chains (2a10) and nine peripheral n-dodecyloxy chains (2a12) form an enantiotropic hexagonal columnar phase, whereas their homologue 2a14, bearing nine peripheral n-tetradecyloxy chains, does not show mesomorphic behaviour. Compound bearing six peripheral n-decyloxy chains, which are in the 3,4-positions of the terminal benzene rings (2c10) does not show mesomorphic properties, whereas its analogous compound 2b10, bearing six n-decyloxy chains in the 3,5-positions of the terminal benzene rings, is liquid. The electrochemical behaviour of the liquid crystalline compounds 2a10 and 2a12 was investigated by cyclic voltammetry which revealed the hole-blocker character of these compounds. The ultraviolet–visible absorption and emission properties of the compounds 2an, 2b10 and 2c10 have been investigated. Photophysical studies were carried out in solution and in film. In addition, solvatofluorochromism studies were performed with compound 2a12 as a representative member of the compounds of series 2.     

Columnar liquid crystalline tris-(ether)triazines with pendant 1,3,4-thiadiazole groups: synthesis,mesomorphic, luminescence,solvatofluorochromic and electrochemical properties

Novel columnar liquid crystals whose molecular structures consist of a C₃ star-shaped 1,3,5-triazine unit as a central core, and three pendant 2-phenyl-5-(di-, and/or tri-n-alkoxyphenyl)-1,3,4-thiadiazole arms, containing ether connecting groups, variable number and positions of linear alkoxy chains were synthesised and their mesomorphic properties were studied by differential scanning calorimetry, polarised optical microscopy and X-ray diffraction. The mesomorphic properties were found to be dependent on the length, position and number of the peripheral alkoxy chains. Most compounds form enantiotropic hexagonal columnar phases. These compounds also show photoluminescent properties in the visible region with good quantum yields. Photophysical studies were realised in solution and in solid state. Also, solvatofluorochromism and cyclic voltammetry studies were performed.     

Columnar bis(pyridinium) ionic liquid crystals derived from 4-hydroxypyridine: synthesis,mesomorphism and emission properties

A series of flexibly linked bis(pyridinium) salts with various counterions (Br^?, PF₆^?, BF₄^? and OTf-) was designed and prepared starting from corresponding N-alkylated 4-pyridones precursors with mesogenic 3,4,5-tris(alkyloxy)benzyl moieties (alkyl = dodecyl or tetradecyl). These salts were investigated for their liquid crystalline properties by a combination of differential scanning calorimetry, polarising optical microscopy and temperature-dependent powder X-ray diffraction (XRD). Their thermal stability was checked by thermogravimetric analysis. All bis(pyridinium) salts, except the triflate salt with shorter terminal carbon chain, display an enantiotropic liquid crystalline behaviour with a hexagonal columnar (Col_h) phase assigned on the basis of its characteristic texture and XRD studies. It was found that these luminescent bis(pyridinium) salts show weak emission in dichloromethane solutions at room temperature and a pronounced red-shifted emission in solid state. The emission properties of these bis(pyridinium) salts do not depend significantly on the nature of counterion employed.     

Synthesis,liquid crystalline properties and fluorescence of polycatenar 1,3,4‐oxadiazole derivatives

A series of hexacatenar liquid crystals containing the 1,3,4‐oxadiazole group as rigid core, i.e. 1,4‐bis[(3,4,5‐trialkoxyphenyl)‐1,3,4‐oxadiazolyl]‐ benzene (P‐P‐oxd‐n), were designed and synthesised. Based on a detailed study of their thermotropic phase behaviour and mesophase structures, it was revealed that columnar phases are generated in these materials. Furthermore, combination of experimental and calculated results enabled a proposal for the molecular packing in the mesophase. The photoluminescent properties of these materials were examined using P‐P‐oxd‐8 as an example. A strong blue light emission (λ_max = 456 nm) was observed in P‐P‐oxd‐8 and a higher quantum yield was obtained in dilute chloroform solution.     

From smectic to columnar phase of polypedal liquid crystals based on tetrathiafulvalene/1,3-dithiol-2-thione and cholesterol

Bipedal 1,3-dithiole-2-thiones attached two cholesteryl through a ω-thioalkanoyloxy spacer of varying length were synthesized. The bipedals were easily transformed to the appropriate tetrapedal tetrathiafulvalene derivatives by self-coupling reaction in net triethyl phosphite. All the synthesized compounds exhibit mesogenic phases in a wide temperature region, no crystallization but vitrifying to form glassy mesogens during cooling from the isotropic melt. The liquid crystals with shorter spacer (n=2-6) exhibited only a smectic A phase and those with the longest spacer (n=7) exhibited only a hexagonal columnar. In these series, the molecular packing depended on the length of spacers.     

Highly birefringent nematic and chiral nematic liquid crystals

We report a simple interference method to determine the dispersion of the extraordinary refractive index and birefringence of highly conjugated and coloured nematic liquid crystals used as light‐emitting materials in organic electroluminescent devices. The measurements are made in the nematic glass phase at room temperature. The birefringence is highly dispersive and values up to 1.1 are obtained. Chiral groups are incorporated into the end chains giving a chiral nematic liquid crystal with a very wide stopband in the visible region. The Berreman matrix method is used to simulate transmission through the chiral nematic liquid crystal cell using the refractive index parameters obtained experimentally. Excellent agreement between theory and experiment is found.     

官能化苯并菲盘状液晶的合成及不饱柔链对介晶性的影响

合成了12个含不饱和软链的苯并菲盘状液晶化合物,C18H6（OC5H11）6-x（OR）x（x=1,2,3）,R=-C3H6CH=CH2（a）,-C3H6C≡CH（b）,-C2H4OCH=CH2（c）.化合物结构通过核磁共振氢谱和高分辨质谱表征.化合物热致液晶性通过偏光显微镜（POM）,差视扫描热量法（DSC）,和X射线衍射（XRD）进行了研究.结果显示目标化合物呈现有序的六方柱状介晶相.端炔基链化合物b系列熔点最高.乙烯氧基柔链化合物c系列有最高的清亮点和最宽的介晶性温度范围,且随着不饱和醚链数的增多,清亮点明显升高.对称苯并菲化合物sym-C18H6（OC5H11）3（OR）3比不对称化合物asym-C18H6（OC5H11）3（OR）3具有更高的熔点和清亮点.乙烯氧基柔链可极化的偶极相互作用对液晶稳定性有较大贡献.     

Imidazolium‐based polymerized ionic liquid crystals containing fluorinated cholesteryl mesogens

A series of polymerized ionic liquid crystals (PILCs) bearing fluorinated cholesteryl mesogens were synthesized in this work, which include polymerized imidazolium bromides (PIBs) and polymerized imidazolium hexafluorophosphates (PIHs). The PIBs were synthesized using alkyl bromine‐containing polysiloxanes and 1‐butyl‐1H‐imidazole, and the PIHs were synthesized by anion metathesis reaction using the corresponding PIBs and KPF₆. The chemical structures, liquid crystalline (LC) properties, and electrorheological (ER) effect of these PILCs were characterized by use of various experimental techniques. All the PILCs showed smectic A mesophase on heating and cooling cycles. The smectic layer structure of these PILCs are originated from the rigid fluorinated cholesteryl mesogens and the flexible moieties in the LC phase, but the ion pairs (imidazolium cations–PF₆^?, Im⁺–PF₆^?; or imidazolium cations–Br^?, Im⁺–Br^?) can disperse in the polysiloxane matrix and expand the d‐spacing in the smectic layers. The PIHs show lower T_g and T_i than the corresponding precursor PIBs, which is due to the larger ion volume of Im⁺–PF₆^? for PIHs than that of Im⁺–Br^? for PIBs. A series of 40 V% ER fluids were prepared by mixing the PILCs with polydimethylsiloxane (PDMS), and the ER behaviors were studied. All the PILC/PDMS fluids showed ER effect, and the PIH/PDMS fluids show a little greater ER effect than the PIB/PDMS fluids. The PILC droplets in the ER fluids become deformed owing to both the orientation of fluorinated cholesteryl mesogens and the suppression of ionic migration when a DC electric field was applied, resulting in the occurrence of ER effect. Copyright © 2015 John Wiley & Sons, Ltd.     

Tuning the Magnetic Properties of Columnar Benzo[e][1,2,4]triazin-4-yls with the Molecular Shape

A homologous series of disc-like 1,3,6-trisubstituted benzo[e][1,2,4]triazin-4-yls 1[n] was synthesized and their structural, thermal, optical, magnetic, and electric properties were investigated. The results demonstrate that all members of the series display a Col_h phase with clearing temperatures depending on the length of the alkoxy chains at the N(1) position, hence the shape of the disc. Powder XRD and magnetic data indicate a gradual change in the column diameter and magnetic behavior in the series in transition from half-disc in 1[0] (antiferromagnetic interactions) to full-disc geometry in the 1[12] homologue (ferromagnetic interactions with J/k_B=+7.5 K). Studies of binary systems revealed that a 1 : 1 mixture of 1[0] and 1[12] exhibits modest stabilization of the Col_h phase with an expanded range, and magnetic behavior typical for 1[0] in the rigid phase obtained from the melt. Electric measurements demonstrated hole mobility of ∼10⁻³ cm² V⁻¹ s⁻¹ and dark conductivity of ∼10⁻¹¹ Scm⁻¹ in the mixture and individual compounds. The latter is enhanced up to 4 times by simultaneous illumination with UV light.     

Hexagonal columnar mesophases of polycatenar para-phenylene connected bis-oxadiazole-based liquid crystals

In this article polycatenar liquid crystals containing two 1,3,4-oxadiazoles interconnected by a para-substituted benzene ring as the central linking unit and three alkoxy chains at each terminal have been synthesised, and investigated by polarising microscopy, DSC and XRD scattering. Molecules with medium chain length form exclusively hexagonal columnar liquid crystalline phases.     

PbS nanoparticles stabilised blue phase liquid crystals

A kind of blue phase liquid crystal (BPLC), consisting of nematic liquid crystal, E7, and chiral dopants, CB15 and R1011, was investigated by doping PbS nanoparticles. The blue phase temperature range was extended from 3^oC to 4.6°C by doping PbS nanoparticles with diameters around 9.6 nm. A kind of porous texture was observed both in the forming process of PbS nanoparticles doped BPLCs as well as in the BPLCs (with/without PbS nanoparticles) under assisting electric field. The porous texture may indicate that the liquid crystals molecule should be reoriented during the formation process of PbS nanoparticles doped BPLCs.     

Thermal behavior of selected ferroelectric liquid crystals

Thermal properties of three ferroelectric liquid crystals, namely: 3-octyloxy-6-[2-fluor-4-(fluoroctyloxy)phenyl]-pyridine (FFP), 3-(3-fluor-nonyl)-6[4-heptyloxyphenyl]-pyridine (FNHPh-P), 4-[(S,S)-2,3-epoxyhexyloxy]phenyl 4-(decyloxy)benzoate (EHPhDB) were studied using heat flux differential scanning calorimetry method. All the transitions expected in this compounds, except the SmC^*-SmA^* and SmC^*-S₃ transitions, were detected in the DSC curves. The temperatures of the phase transitions and the enthalpy changes associated with them were determined. The transition from the liquid crystalline to the crystalline state showed significant hysteresis for all three compounds studied. The following transitions: SmA^*-Is, SmG^*-SmC^* for FNHPh-P, N^*-Is for EHPhDB, N^*-Is and SmC^*-N^* for FFP also showed a small hysteresis basing on which first-order character of all the above transitions was implied. All three substances studied in this work are characterized by a complex polymorphism in the solid state.The author is grateful to Dr. Stanislaw Wróbel for his stimulating interest, valuable discussions and supplying the samples. This work has been done in the framework of the KBN grant 2 P302 139 07.     

Magnetic anisotropy of liquid crystals based on lanthanide mesogenic complexes

The values of magnetic anisotropy of smectic A-phases for a number of lanthanide complexes (LH)₂LM(NO₃)₂, where M=Nd, Eu, Gd, Tb, Dy, Ho, and Er, and LH is a Schiff's base), were measured. These values are two orders of magnitude larger than those normally found for diamagnetic liquid crystals and are well correlated with magnetic birefringence constants and molecular mangetic anisotropy of nomesogenic lanthanide diketonates. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 694–697, April, 1999.     

Towards a new class of ferroelectric liquid crystal molecules for nonlinear optical applications

The synthesis of a new molecule specifically designed to exhibit both ferroelectric and nonlinear optical properties is presented. This molecule possesses an optically active phenyl sulphinic group, which introduces a dipole moment directly linked to the chromophore group, with a nitro group in the meta -position. The rest of the molecule comprises a tolane and a benzoate group. Such a structure results in an enantiotropic smectic C*-smectic A phase sequence in its polymorphism. A first measurement of the spontaneous polarization shows a high value. The polymorphism of the racemic homologous molecule possessing the nitro group in the ortho-position is also presented, and also shows the smectic C-smectic A phase sequence.     

New azobenzene containing bent-core liquid crystals based on disubstituted resorcinol

New bent-core molecules with 4,6-dichlororesorcinol or 4-chloro-2-methylresorcinol as the central unit, and azobenzene with different alkyloxy chain length as side arms were synthesised. The mesophase behaviour of the new compounds was investigated by polarising optical microscopy, differential scanning calorimetry, X-ray diffraction studies and electro-optical measurements. It is found that 4,6-dichlororesorcinol is more conducive towards mesomorphism than 4-chloro-2-methylresorcinol. The liquid crystalline properties of all of the prepared compounds are greatly affected by the lateral substitution on the outer ring. 4,6-Dichlororesorcinol-based compounds without lateral substitution show nematic phases with cybotactic cluster of the SmC-type (N_CybC). Moreover, depending on the chain length, the nematic phase appears as enantiotropic phase for the shortest homologue and as monotropic phase for the higher homologues.