Synthesis,characterisation and liquid crystal properties of 2,5‐bis[5‐alkyl(alkoxy)phenyl‐1,3,4‐oxadiazole]bromobenzenes

A series of new thermal bilateral liquid crystal compounds with the phenylenebis‐1,3,4‐oxadiazole structure was synthesised. The molecular structures of the oxadiazole compounds were confirmed by FT‐IR and ¹H NMR spectroscopy, elemental analysis and mass spectrometry. Thermogravimetric analysis indicates that the compounds in an atmosphere of nitrogen have good thermal stability. Measurements using differential scanning calorimetry, polarising optical microscopy and temperature‐dependent wide‐angle X‐ray diffraction indicated that the liquid crystalline properties are related to the length of the end groups. When the end group was tert‐butyl or alkoxy with four and six carbons, the compounds exhibit no liquid crystal phase. However, compounds with end groups containing more than eight carbons show significant bidirectional thermally‐induced liquid crystal properties and the structure of the liquid crystal phase is the lamellar smectic A phase. All the compounds exhibit blue fluorescence.     

Synthesis and properties of non-symmetric liquid crystal dimers containing a cholesteryl moiety

A series of non-symmetric liquid crystal dimers having cholesteryl and 4-trans-(4-n-alkylcyclohexyl)phenoxy groups were synthesized by condensation of cholesteryl ω-bromoalkanoates with appropriate 4-trans-(4-n-alkylcyclohexyl)phenols. The structures and thermal phase behaviour of the dimers were characterized using IR, ¹H NMR and mass spectroscopy, elemental analysis, differential scanning calorimetry, polarizing optical microscopy and X-ray diffraction measurements. Their thermal phase behaviour is significantly different to that of other cholesterol-based liquid crystal dimers. All of these liquid crystal dimers exhibit low phase transition temperatures. The relationships between their properties and chemical structures of these new dimers are discussed.     

Amide as Terminal Groups: Synthesis and Properties as New Tolane‐Type Liquid Crystals

A series of novel tolane‐type liquid crystals with amide group as terminal group have been prepared. The terminal amide groups were modified, and the influence of these structural parameters on liquid crystal phases was investigated by polarizing optical microscope (POM) and differential scanning calorimetry (DSC). Three of these new compounds exhibit nematic phase, good thermal stabilities. In general, these liquid crystals with amide as end groups have high melting points and phase transition temperatures, which result from the hydrogen bonds. Based on theoretical calculations, these new molecules with strong electron donating amide as end group have narrower HOMO‐LUMO energy gap and higher dipole moment than tolane.     

Synthesis and mesophase behaviour of mesogens bearing omega, alpha, alpha-trihydroperfluoroalkoxy end tails

One series of two-ring and two series of three-ring liquid crystal compounds, all containing omega, alpha, alpha-trihydroperfluoroalkoxy terminal tails, were prepared and characterized by IR, NMR, MS and elemental analysis. Their phase transition behaviour was investigated by DSC and polarizing optical microscopy. Biphenylene derivatives with the omega, alpha, alpha-trihydroperfluoroalkoxy end group form a stable smectic A phase. In the three-ring system, biphenylene ester compounds exhibit a smectic phase without a nematic phase. The compounds exhibit smectic A and smectic C phases when the terminal groups are intermediate length alkyl and fluorinated alkyl chains. Mesogens with fluorinated tails have a broader smectic C phase than the non-fluorinated mesogens.     

Synthesis and characterization of thiophene-containing liquid crystals

Six series of liquid crystal materials containing a 2,5-disubstituted thiophene unit were synthesized. The liquid crystal compounds obtained were characterized by NMR, differential scanning calorimetry, polarizing optical microscopy and X-ray diffraction techniques. The properties of liquid crystalline phases were investigated as a function of spacer units, number of aromatic core rings and different terminal moieties. Cyano, methoxy and iodo groups were used as terminal groups. It is found that: (i) compounds having one thiophene ring and one phenyl ring connected by an ester group, with a length/breadth value of 2.1, exhibit no mesophase, while other compounds containing two biphenyl rings, with a length/breadth ratio of 2.7, show mesophases; (ii) the polarity of terminal groups and the flexible spacer length significantly affect the thermal behaviour of these compounds; (iii) the nematic transition range of cyano-containing compounds decreases with increasing length of the flexible spacer, and long alkenyloxy chains tend to facilitate the formation of the smectic phase and suppress the nematic phase in all the mesogenic compounds synthesized.     

Synthesis and characterization of thiophene-containing liquid crystals

Six series of liquid crystal materials containing a 2,5-disubstituted thiophene unit were synthesized. The liquid crystal compounds obtained were characterized by NMR, differential scanning calorimetry, polarizing optical microscopy and X-ray diffraction techniques. The properties of liquid crystalline phases were investigated as a function of spacer units, number of aromatic core rings and different terminal moieties. Cyano, methoxy and iodo groups were used as terminal groups. It is found that: (i) compounds having one thiophene ring and one phenyl ring connected by an ester group, with a length/breadth value of 2.1, exhibit no mesophase, while other compounds containing two biphenyl rings, with a length/breadth ratio of 2.7, show mesophases; (ii) the polarity of terminal groups and the flexible spacer length significantly affect the thermal behaviour of these compounds; (iii) the nematic transition range of cyano-containing compounds decreases with increasing length of the flexible spacer, and long alkenyloxy chains tend to facilitate the formation of the smectic phase and suppress the nematic phase in all the mesogenic compounds synthesized.     

Synthesis and mesomorphism study of star‐shaped carbohydrate liquid crystals containing glucosyl and glutamyl residues

A series of novel star‐shaped carbohydrate derivative liquid crystals was synthesized with glucose as the chiral core structure. Glutamyl mesogenic moieties, l‐R‐{n‐[4‐(cholesteryloxycarbonyl)benzoyloxy]alkoxy}glutamic acid, were introduced to the five hydroxy groups of glucose by direct esterification. The chemical structures of the target liquid crystalline compounds were confirmed by element analysis and Fourier transform infrared, ¹H NMR and ¹³C NMR spectroscopy. The mesomorphic behaviour and thermal properties of target liquid crystalline compounds were investigated with differential scanning calorimetry, thermogravimetric analysis, polarizing optical microscopy, X‐ray diffraction and specific rotation. All the target compounds exhibit a cholesteric liquid crystalline phase. These compounds demonstrate a wide mesogenic region and high thermal stability. The effect of flexible spacer group length of the target compounds on the molecular structure and thermal properties is discussed.     

Synthesis and mesomorphic properties and optical behaviour analysis of homologous series azobenzene liquid crystal monomer with polar substituents

ABSTRACT

Twenty novel azobenzene liquid crystal micromolecular compounds named ω-[4-(p-substituted azobenzeneoxy carbonyl]acid (X-ABCnA) have been designed and synthesised, followed by studies on the thermal performance and mesomorphic properties of the compounds. The liquid crystal compounds were divided into five homologous series based on the terminal substituents R (R = CH₃O, CH₃, H, Cl, NO₂). In each series, the number of carbons on flexible chain was 4, 6, 8 and 10, respectively. Fourier-transform infrared, proton nuclear magnetic resonance and elementary analysis demonstrated that the structure of the synthesised azobenzene liquid crystal compounds was consistent with the molecular design. The mesomorphic properties were tested, analysed and characterised by using differential scanning calorimetry and polarised optical microscopy. The melting transition (T _m) of all the compounds in homologous series with different substituents appeared to decrease with the increase of carbon numbers on flexible chains. The same held true for the temperature of isotropic-mesophase/crystalline transition. The compounds with stronger polarity of terminal substituents were more likely to form broader mesogenic ranges. The liquid crystal compounds discussed in this work can be regarded as a reference for the synthesis of mesogenic arms participating in the synthesis of novel multi-arm liquid crystalline macromolecules and polymers.     

Properties of meso-tetrakis (4-n-alkanoyloxyphenyl) porphyrin liquid crystal Co and Ni complexes

Six series of meso-tetrakis (4-n-alkanoyloxyphenyl) porphyrin Co and Ni complexes (12 kinds) were reported. Nine of the compounds were found to exhibit liquid crystal properties and display a hexago-nal columnar discotic columnar (Colh) phase. Molecular structure of all synthesized compounds was confirmed by IR, UV, MS, 1H NMR, and elemental analysis. These liquid crystalline compounds have been studied by cyclic voltammetry, luminescence, and surface photovoltage spectroscopy.     

μ-氧-双[meso-四(对烷氧基苯基)卟啉合铁(III)]的合成、表征和液晶性

设计合成了未见文献报道的μ-氧-双[meso-四(对烷氧基苯基)卟啉合铁(III)]配合物9个, 研究了其合成、分离、纯化方法, 用MS, ¹H NMR, IR, UV, 元素分析等方法剖析确证了目标化合物的结构, 其结构我们认为是μ-氧桥联的二聚体结构, 且存在两种典型空间构象结构(重叠式和交叉式), 表现为同一系列化合物存在四类¹H NMR谱. 用差示扫描量热仪和偏光显微镜研究了这9个化合物的液晶性, 发现9个化合物均具有液晶性, 多为升温降温互变液晶, 具有丝状光学织构. 有一至三个中介相, 相变起始温度最低为－6 ℃, 最高为210 ℃; 相变区间最宽为301 ℃, 最窄为50 ℃; 清亮点(T_c)最高315 ℃, 最低147 ℃. 考察了烷氧基链长、配位金属离子及配合物分子空间结构对液晶性能的影响. 我们认为这种μ-氧桥联的二聚体结构比单层平面卟啉及其金属配合物具有更好的液晶性.     

氯化meso-四(对烷氧基苯基)卟啉合铁(Ⅲ)的合成、表征和性能

设计合成了10个氯化meso-四(对烷氧基苯基)卟啉合铁(Ⅲ)配合物, 其中7个尚未见文献报道. 用1H NMR, MS, IR, UV和元素分析等技术表征了该系列配合物的结构. 用差示扫描量热法和偏光显微镜研究结果表明8个配合物具有液晶性, 其液晶行为分别表现为升温单变液晶和升温降温互变液晶; 有1~2个中介相, 相变区间Δt最宽为128 ℃, Δt最窄为42 ℃, 液晶起始相变温度最高为80 ℃, 最低为42 ℃; 清亮点tc最高为181 ℃, 最低为110 ℃; 考察了烷氧基链长、配位金属离子及配合物分子空间结构对液晶性能的影响. 通过荧光光谱分析进一步验证了氯化卟啉合铁(Ⅲ)可以转化为μ-氧-双卟啉合铁(Ⅲ).     

偶氮型液晶冠醚的合成与表征

以4'-正烷氧基联苯-4-甲酸和顺(反)-4,4'-双(4-羟基苯基偶氮)二苯并-14-冠-4为中间体, 通过溶液缩合反应, 合成了一系列偶氮型液晶冠醚. 并用元素分析、核磁共振、紫外可见分光光度计、红外光谱、基质辅助激光解析电离飞行时间质谱、示差扫描量热法和偏光显微镜对其进行了表征. 随分子末端烷氧基碳原子数增加, 化合物4I和4II的熔点(T_m)和液晶态的清亮点(T_i)逐渐降低, 液晶态温度范围较宽.     

Synthesis and mesomorphic properties of new Schiff base esters with different alkyl chains

A new series of Schiff base esters,4-(dimethylamino)benzylidene-4'-alkanoyloxyanilines containing even number of carbons at the end group of the molecules(C_(n-1)H_(2n-1)COO,n = 6,8,10,12,14,16,18) were synthesized.The present compounds were monotropic liquid crystals.It was also found that the end groups of the molecules had effect on the mesomorphic properties.     

Side-chain liquid-crystalline copolymers containing charge transfer groups

A series of side-chain liquid crystal copolymers have been prepared based on a polystyrene backbone and having 4-nitro-4'-oxyazobenzenealkyloxy and 4-methoxy-4'-oxyazobenzenealkyloxy pendant groups. All the polymers exhibit solely smectic behaviour. The thermal stability of the smectic phase is significantly enhanced in the copolymers when compared to the homopolymers. This is compared to the behaviour of the analogous monomeric compounds. The enhancement of the thermal stability is attributed to a specific interaction, possibly charge transfer.     

Electrooptical properties of new type fluorinated phenyl-tolane isothiocyanate liquid crystal compounds

A series of 4?-(4-alkyl-phenyl)-2?,6?-difluorotolane isothiocyanate liquid crystal (LC) compounds were synthesised, and their phase transitions and electrooptical properties were investigated. These compounds exhibit high birefringence, about 0.47–0.52. As the number of carbon atoms in the alkyl chains increases, these LC compounds can exhibit smectic phases. When these LCs were mixed into the commercial LCs, the birefringence values of LC mixtures become higher than pure commercial LCs, and the visco-elastic coefficients of five LC mixtures are very close to each other at every test temperature. The results of response properties indicate that the compounds with a tri-fluorine substitution and n-propyl end group possess better response performance than the others. These LC compounds are particularly attractive for achieving fast response times in LC optic devices.     

Highly fluorinated liquid crystals with wide nematic phase interval and good solubility

A series of new liquid crystal compounds with both ethylene and difluoromethyleneoxy linking groups have been synthesised and their physical properties were measured. The compounds exhibit lower melting points and broader nematic mesophase temperature range than that of corresponding four-rings compound. Their anisotropic properties are Δε of about 25 and Δn of 0.135. The investigation shows that their solubilities are much better than that of reference compound. A mixture made by equivalent mass ratio of the compounds with side chain of ethyl, propyl and pentyl is found to keep nematic phase from 12°C°C to 109°C, which is rarely observed in highly fluorinated liquid crystals.     

Acetylene-containing highly birefringent rod-type reactive liquid crystals based on 2-methylhydroquinone

New highly birefringent reactive liquid crystal materials based on the 2-methylhydroquinone core were designed and synthesised. Rod-type liquid crystal compounds bearing photo-crosslinkable reactive group of acryloyl, methacryloyl, cinnamoyl, furylacryloyl group were synthesised by introducing acetylene groups via Sonogashira coupling to obtain high birefringence, and lateral groups such as fluoro and methyl to adjust the temperature of the liquid crystal phase. The synthesised compounds were characterised using nuclear magnetic resonance spectroscopy, mass spectrometry and elemental analysis. In addition, their thermal behaviour was investigated using differential scanning calorimetry and polarised optical microscopy. After aligning the synthesised compounds, liquid crystal films were prepared by photo-irradiation. Photo-elastic modulator results showed that the obtained liquid crystal films had high birefringence (Δn) values of 0.32–0.40.     

Laterally fluorinated phenyl biphenylcarboxylates; versatile components for ferroelectric smectic C mixtures

Twenty-six fluoro-substituted 4-n-alkoxyphenyl 4'-n-alkyi-and 4'-n-alkoxybiphenyl-4-carboxylates are reported. The number and position of the fluoro groups influences the liquid crystal phase sequence and has a dramatic effect on the liquid crystal transition temperatures. Some compounds have low melting points and a very wide smectic C phase, whereas other compounds exhibit a very wide smectic A phase. Compounds containing a 2,3-difluorophenyl group provide useful materials which have a large negative dielectric anisotropy.     

Synthesis and physico-analytical studies of some novel ferrocenyl Schiff base derivatives

A series of ferrocenyl Schiff base derivatives was synthesized by condensation reactions of 1,1′-ferrocenedicarboxaldehyde and aromatic amines containing long chain alkyl groups as free ends which were characterized by their physical properties, elemental, FTIR, ¹H NMR, ¹³C NMR spectral and thermal analysis. The thermal behaviour of the synthesized compounds was studied by differential scanning calorimetry (DSC) which revealed that these compounds may exhibit mesomorphic properties. The DSC results of aromatic amines and ferrocenyl Schiff bases were compared to study the effects of structure, i.e. rigid core and terminal chain length, on the phase transition behaviour.     

分子中部含齐聚氧化乙烯单元的酯-醚液晶

以4-(4′-烷氧基苯甲酰氧基)苯甲酸作为液晶中间体,合成了在分子中部含齐聚氧化乙烯的系列酯-醚液晶化合物.对其化学结构和液晶性能进行了表征,除个别化合物外,其余样品均具有热致液晶性.