反式-环己基含氟二苯乙炔类液晶的合成与性能

反式-环己基含氟二苯乙炔类液晶的合成与性能;烷基环己酮;顺、反异构体转换;光学各向异性     

新型含酰胺键的噻二唑类液晶的合成

合成了以酰胺键为中心桥键的1,3,4-噻二唑衍生物3个系列共16个新化合物。液晶性质测试表明,它们均为具有高相变温度和宽相变范围的稳定液晶化合物。说明极性的酰胺键有利于介晶性能。比较了端某碳原子数目的多寡对S_c相相变温度的影响。     

新型吡啶环液晶化合物的合成及性能

以2-溴-5-吡啶甲醛和5-溴-2-吡啶甲醛为起始原料,合成出4种新型含吡啶环二联芳基和三联芳基化合物,总收率20%~30%。 热性能研究结果表明,二联芳基化合物未呈现出液晶相,而三联芳基化合物在加热和冷却过程中均表现向列相液晶态,且当氮原子位于正丁基的间位时,其与不含氮原子的三联苯化合物(2c)相比,熔点降低了11.7 ℃,清亮点升高6.3 ℃,液晶相区拓宽了18 ℃,表现出了良好的热性能。 光电性能测试结果表明,用吡啶环替代苯环后,化合物的光学各向异性值均较参比化合物(1c或2c)增大;当N原子位于正丁基的邻位的化合物,介电各向异性值较参比化合物增大,且液晶的阈值电压、饱和电压均降低。 通过对三环同分异构体化合物的不同构象能量态的计算分析,解释了介电各向异性的变化规律。     

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).     

二代树状碳硅烷液晶研究——端基含36个己氧基偶氮苯介晶基元

用发散法合成周边含36个己氧基偶氮苯介晶基元(M3)端基的新的二代树状碳硅烷液晶(D2),并用元素分析、氢谱、激光质谱、红外光谱、紫外-可见光谱、偏光显微镜,DSC和WAXD法进行表征.D2为向列相,与M3相同.D2液晶态相行为是K90N105I1l3N75K,D2熔点比M3降低2633℃,D2清亮点比M3降低315℃,D2液晶态温区比M3加宽1130℃.D2和一代树状物D1的相态由介晶基元相态决定.D2熔点比D1降低23℃.D2清亮点比D1降低1121℃,D2液晶态温区比D1减少819℃.     

电视用液晶材料的研究进展

液晶电视由于其优异的显示性能将会越来越受到青睐.本文简要综述了近年来电视用液晶材料的研究进展,归纳总结了这些液晶材料的合成方法及其热性能、介电各向异性、双折射率、粘度等特性.     

(硫杂)杯[4]芳烃缩氨基(硫)脲(桥联)衍生物的合成

对叔丁基(硫杂)杯[4]芳烃-1,3-二醛基衍生物4a和4b与苯基氨基硫脲进行“1＋2”缩合反应, 合成了杯[4]芳烃缩氨基硫脲衍生物5a和5b, 产率为84%和85%. 化合物4a和4b与1,6-己基双氨基脲发生“1＋1”缩合反应, 合成了杯[4]芳烃双缩氨基脲桥联衍生物6a和6b, 产率为83%和80%. 新化合物的结构与构象经元素分析、质谱、核磁共振谱等表征证实.     

基于定向电纺纤维膜的可调制偏振片的制备

基于定向静电纺丝技术制备了高取向性有序纤维薄膜, 利用有序纤维对液晶分子取向的诱导, 构建了可调制散射型偏振片. 填充混合液晶的有序聚甲基丙烯酸甲酯纤维薄膜在可见光范围内, 表现出明显的偏光特性. 混合液晶中光敏性偶氮液晶4-正丁基-4'-甲氧基偶氮苯在360 nm紫外光照射下进行顺反异构转变, 诱导混合液晶发生从各向异性到各向同性的相变. 利用混合液晶光致相变与有序纤维的耦合, 实现了薄膜偏光特性的光控切换.     

端基含4个丁氧基偶氮苯介晶基元光致变色液晶树状物的光化学研究

研究了新化合物含4个丁氧基偶氮苯介晶基元的零代(D0)光致变色液晶树状物在氯仿和四氢呋喃中的吸收光强、最大吸收波长、摩尔消光系数、量子产率、活化能、异构转换率、反-顺光异构化反应速率常数、热回复异构化反应速率常数、光回复异构化反应平衡常数及速率常数．D0的光致变色反应速率常数为10^-1s^-1,而含偶氮基元液晶聚硅氧烷的光致变色反应速率常数为10^-8s^-1,因此液晶树状物D0的光响应速度比后者快10^7倍．     

二代树状碳硅烷液晶研究Ⅰ.端基含36个丁氧基偶氮苯介晶基元

用发散法合成周边含36个丁氧基偶氮苯介晶基元(M5)端基新的二代树状碳硅烷液晶(D2),并用元素分析,氢谱,激光质谱,红外,紫外,偏光显微镜,DSC和WAXD法表征.D2为向列相,与M5相同,二代树状物相态由介晶基元相态决定.D2液晶态相行为是K85N107I103N69K,其熔点比M5降低27～41℃,清亮点比M5降低17～18℃,液晶态温区比M5加宽10～23℃.二代碳硅烷(D2)与一代碳硅烷(D1)相比熔点增加2～3℃,清亮点降低26～29℃,液晶态温区减少29～31℃.在二代树状物中观察到S=+3/2的高强向错.     

High birefringence and large negative dielectric anisotropy phenyl‐tolane liquid crystals

Two phenyl‐tolane compounds with two pairs of (2,3) lateral difluoro substitutions were synthesized and their properties evaluated. These compounds exhibit a high birefringence (Δn ～ 0.35) and a large negative dielectric anisotropy (Δε～ ?8). These two important features make the phenyl‐tolane compounds useful as a dopant in a negative Δε liquid‐crystal mixture to enhance the performance of the host mixture, or as a negative component in a dual‐frequency liquid‐crystal mixture to improve the dielectric anisotropy and birefringence and lower the crossover frequency.     

新型二氟乙烯端基异硫氰酸酯化合物的合成及性能

以对碘苯甲醛和二氟氯乙酸钠为原料,经5步反应合成了4个新型二氟乙烯端基异硫氰酸酯化合物,经气相色谱(GC)检测纯度均大于98.7%,总收率为23%~31%.采用红外光谱(IR),核磁共振波谱(NMR)和质谱(MS)等技术对化合物的结构进行了表征.通过差示扫描量热(DSC)法和偏光显微镜(POM)研究了化合物的介晶性,采用外推法得到了化合物的双折射率和旋转黏度值.结果表明,化合物A1~A3均呈现较宽的互变向列相;用二氟乙烯基替代乙基后,化合物的向列相拓宽了31~62℃,双折射率提高了0.038~0.052,旋转黏度降低.基于新型二氟乙烯基异硫氰酸酯化合物的高双折射率混合液晶配方具有更宽的向列相温度范围、更高的双折射率、更低的旋转黏度及更高的品质因子.     

Synthesis and properties of high birefringence liquid crystals: thiophenylacetylene and benzothiazolylacetylene derivatives

We have synthesized and evaluated the physical properties of thiophenylacetylene and benzothiazolylacetylene derivatives in order to obtain higher Δn liquid crystals as compared with analogous phenylacetylene-based compounds. These new materials had poorer liquid crystallinity than the phenylacetylene derivatives. Exchanging the phenyl ring for a benzothiazole ring was effective in increasing Δn, whereas a thiophene ring decreased Δn because of the associated reduction in the anisotropic polarizability. These conjugated hetero rings shifted the UV absorption spectra into the visible region such that they are yellow or brownish in colour.     

Synthesis and mesomorphic properties of fluoro and isothiocyanato biphenyl tolane liquid crystals

Four series of high birefringence biphenyl tolane liquid crystals having a terminal isothiocyanato or fluoro group were synthesized; their mesomorphic properties were studied by optical polarizing microscopy and DSC. These biphenyl tolane compounds exhibit reasonably low melting points and high birefringence of 0.37-0.49. By using these compounds a eutectic mixture was formulated exhibiting a wide nematic range, high figure-of-merit and low viscosity.     

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 mesomorphic properties of fluoro and isothiocyanato biphenyl tolane liquid crystals

Four series of high birefringence biphenyl tolane liquid crystals having a terminal isothiocyanato or fluoro group were synthesized; their mesomorphic properties were studied by optical polarizing microscopy and DSC. These biphenyl tolane compounds exhibit reasonably low melting points and high birefringence of 0.37–0.49. By using these compounds a eutectic mixture was formulated exhibiting a wide nematic range, high figure‐of‐merit and low viscosity.     

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.     

Synthesis and characterization of new series of ferroelectric liquid crystals containing oligooxyethylene spacers

Four series of ferroelectric liquid crystals containing oligooxyethylene spacers have been synthesized. These obtained liquid crystal compounds were characterized by NMR, differential scanning calorimetry (DSC) and optical polarized microscopy (POM). The properties of the liquid crystalline phase were investigated as a function of spacer units, numbers of core aromatic rings, and different terminal asymmetric moieties. It was found that (i) the phase transition temperature decreased with the increasing oligooxyethylene spacer unit, (ii) the liquid crystalline phases were enhanced in three phenyl ring system than in two phenyl ring system, and (iii) ferroelectric liquid crystals containing different terminal asymmetric moieties exhibited novel mesophase phenomena. A twist grain boundary phase (TGB_A phase) was observed in some compounds of this study. Furthermore, a wide temperature chiral smectic Crange including room temperature was achieved.     

The forgotten liquid crystals of Daniel Vorlander: A new look at mesogenic 4-pyridones

Three classes of 4-pyridone (1H-pyridin-4-one) terminated liquid crystals were synthesized and their mesogenic properties examined. These liquid crystal classes differ in the composition of the aromatic core group which vary among azobenzene, stilbene or tolane groups. The synthesis of the 4-pyridones was accomplished by aromatic nucleophilic substitution reaction of the appropriate activated aryl fluoride with 4-hydroxypyridine. These pyridone liquid crystals possess broad enantiotropic nematic and smectic A phases and may possess useful properties such as high birefringence and polarity including hydrogen bonding capability. The original report of a 4-pyridone containing liquid crystal due to Vorlander has been substantiated.     

Liquid crystal birefringence for millimeter wave radar

Abstract

Many liquid crystals are found to have relatively high birefringence (Δn) values in the microwave and millimeter wave regions, as calculated from the phase shift induced by their reorientation by magnetic or electric fields. At 30 GHz, Δn values were obtained in the range of 0.08 to 0.18 for eleven liquid crystal mixtures of various types. The most favourable liquid crystal structures for high millimeter wave birefringence are highly conjugated rod-like molecules containing biphenyl, terphenyl, phenylpyrimidine, biphenylpyrimidine, and tolane groups in nematics of positive dielectric anisotropy (Δε). However, other liquid crystal structures including Schiffs base, azoxybenzene, and aromatic ester groups also have substantial birefringence, including nematics with negative and crossover Δε, as well as cholesteric nematics. The Δn varied only slightly at different frequencies of microwave millimeter wave in the 15–94 GHz range. Studies on magnetic and electrical field liquid crystal orientation in specially designed waveguides provide a basis for new types of modulators and scanning array antennae in the millimeter wave region, where more compact liquid crystal modulation media can be used than in the microwave region. These scanners can be used for both sending and receiving radar signals for potentially low cost radar systems.