Ferroelectric liquid crystals induced by dopants with axially chiral 2,2'-spirobiindan-1,1'-dione cores: diether vs. diester side-chains

A series of axially chiral 5,5'- and 6,6'-dialkanoyloxy-2,2'-spirobiindan-1,1'-dione dopants, (R)-2 and (R)-4a-4c were synthesized in optically pure form and their ferroelectric polarization powers, δ_p, measured in four liquid crystal hosts with isotropic (I)-nematic (N)-smectic A (SmA)-smectic C (SmC) phase sequences. The results show that the sign of polarization P _S induced by (R)-2 and (R)-4a-4c follows the same trend as that previously reported for the 5,5'- and 6,6'-diheptyloxy-2,2'-spirobiindan-1,1'-dione dopants, (R)-1 and (R)-3. The polarization induced by (R)-2 in the host DFT is below detection limits, and the sign of P _S was found to invert as a function of temperature at mole fractions as low as 0.01. On the other hand, the polarization power of the 6,6'-diheptanoyloxy dopant (R)-4b in the host NCB76 is -1449 nC cm^-2, the fourth highest value reported so far, and more than three times the δ_p value of the 5,5'-diheptanoyloxy analogue (R)-2 in that host (+474 nC cm^-2). Results of ²H NMR experiments suggest that (R)-4b exerts stronger local perturbations in NCB76 than (R)-2, and that these perturbations may be chiral in nature.     

A comparison of mesogenic properties of p-carborane-1,12-dicarbaldehyde schiff's bases with their terephthaldehyde analogues

A homologous series of carborane-containing Schiff's bases 1A[n] (n = 1-10) was prepared and compared with the analogous series 1B[n] derived from terephthaldehyde. An exponential fit of the T _NI values for both series yielded a quantitative assessment of the effect of ring structure on mesophase stability. This includes the T _NI value for n→∞ (86°C for 1A[n] and 209°C for 1B[n]) and steepness of descent (0.135 for 1A[n] and 0.095 for 1B[n]). The difference in behaviour of the two series was attributed, largely, to conformational properties of the central rings A and B. Electronic interactions between the central rings and the π-substituents were investigated by UV spectroscopy and by quantum-mechanical calculations. The effect of replacement of O with CH₂ in the terminal chain of 1[n] on the namatic phase stability was assessed for n = 5-7.     

Two Zinc(Ⅱ) Complexes Based on 7rany-(1R,2R)-cyclohexanediamine: Molecular Structure Analyses and Preparation of Composite Membrane

Two novel complexes Zn2(chda)2(TPA)Cl2(1) and [Zn(chda)2(H2O)2](TPAXH2O)2(2)[chda is a chiral ligand of trans-(1R,2R)-cyclohexanediamine, H2TPA is terephthalic acid] were synthesized at room temperature. The molecular structures of complexes 1 and 2 were identified by single-crystal X-ray diffraction measurement. The results showed that complex 1 had a binuclear structure, each Zn(Ⅱ) ion was four coordinated by two N atoms of chda, one O atom of TPA and one Cl atom, to construct a distorted tetrahedral geometry. For complex 2, the Zn(Ⅱ) ion was six coordinated by two chda molecules and two water molecules to form a ZnN4O2 octahedral geometry. Complexes 1 and 2 further extended into three-dimensional supramolecular frameworks by hydrogen-bonding interactions. Hirshfeld surface analysis and fingerprint plots were used to further analyze the contribution of diflerent intermolecular interactions. Further, a composite membrane [Zn(chda)2(H2O)2](TPA)(H2O)2/CA was prepared by adding 10%(mass fraction) of complex 2 into cellulose acetate using acetone/chloroform( V:V-1:1) as solvent.     

Induced smectic C* phases

Induced ferroelectric S*_C phases are formed by non-chiral S_C host phases doped with chiral dipolar guest molecules. In those mixtures the spontaneous polarization P_s and the tilt angle Θ has been investigated as a function of the mole fraction x_G of the chiral dopant. In most cases the reduced polarization P₀ = P_S/ sin Θ has been found to depend linearly on x_G. The polarization power which is defined by δ_P=(∂P₀/∂x_G)ΔT is discussed in terms of the molecular structure of the chiral dopants. There are systems in which P₀(x_G) deviates positively from linearity. This behaviour can be understood by considering a local field correction to P₀. By assuming a local field of Lorentz type a theoretical relation for P₀(x_G) has been derived which explains the experimental results. The effect of a local field is considerable if the transverse dipole moment and the polarizability of the chiral dopant are large.     

Heterocyclic columnar pyrimidines: synthesis, characterization and mesomorphic properties

The synthesis, characterization, and mesomorphic properties of two series of heterocyclic compounds derived from a pyrimidine core are reported. These series, 1a and 1b, are substituted with a variety of functional groups (X=NHSO₂CF₃, F, Cl, Br, I, OCH₃, CH₃, C₂H₅) at the C^3' (meta)- or C^4' (para)-position of the terminal phenyl ring, and the substituent effect on mesophase formation was studied. The compounds were characterized by ¹H and ¹³C NMR spectroscopy and elemental analysis, and the mesomorphic behavior of the compounds was characterized and studied by differential scanning calorimetry, polarizing optical microscopy and powder X-ray diffraction. Most of the compounds were mesogenic at room temperature, and the mesophases were assigned as lamellar columnar (Col_L) phases, as expected for disk-like molecules. The results also revealed that compounds with a para-substituent (1a; except for -OCH₃) at the C^4'-position, exhibited higher clearing temperatures and wider temperature mesophase ranges than those of compounds with a meta-substituent (1b) at the C^3'-position. The higher clearing temperatures may be attributed to stronger dipolar interactions resulting from a greater resonance effect with the central core for para-substitution than for meta-substitution. The results also indicated that the columnar mesophases observed show a correlation with the electronic properties of the substituents; compounds containing electron-withdrawing substituents (X=F, Cl, Br, I, NHSO₂CF₃) also have higher clearing temperatures than compounds containing electron-donating substituents (X=Me, Et, OMe).     

Liquid crystalline properties of dissymmetric molecules IV. The substituent effect on thermal properties of nematic and smectic A phases in three aromatic ring systems with ester linkages

This paper describes the effect of substituent and ester linkage on smectic properties for some derivatives of 4-R -phenyl 4-(4-octyloxybenzoyloxy)benzoates (1 ), 4-octyloxyphenyl 4-(4-R-benzyloxy)benzoates (2), 4-(4-octyloxybenzoyloxy)phenyl 4- R -benzoates (3), and 4-R-phenyl 4-octyloxyphenyl terephthalates (4) where R = OCH₃, CH₃, OC₈H₁₇, C8H17, halogens, CF₃, OCF₃, CN, NO2, etc. The thermal properties are discussed in terms of the electrostatic nature of the substituents and the relative orientation of the ester groups with respect to both terminal substituents. The substituent effect on the layer structure of the smectic A phase is also examined by means of a small angle X-ray analysis.     

Deuterium NMR studies of inositol liquid crystals [1]

Deuterium NMR investigations are presented on members of two new mesogenic series derived from the naturally occurring stereoisomers myo- and scW/o-inositol. Tetraethers of these two series exhibit thermotropic columnar phases in which the columns are apparently formed by stacked hydrogen bonded dimers of these molecules which chemically are vicinal diols. Deuterium NMR measurements were performed on the tetraoctyl homologues 2e (a cis diol) and 3e (a trans diol) of these series. We have investigated mixtures of these diols with small amounts of benzene-d₆ as probe molecules as well as samples of the neat diol compounds deuteriated at their hydroxyl groups. The results obtained show that the mesophases of both compounds are uniaxial and align partially in a magnetic field upon slow cooling from their isotropic liquids. The alignment is with the director parallel to the field direction indicating that the anisotropic magnetic susceptibility of this mesophase is positive. The deuterium quadrupole splitting of the benzene-d₆ probe in both systems is temperature dependent and in the trans diol 3e it even changes sign. This is interpreted in terms of a model in which the benzene-d₆ probe equilibrates rapidly between two (or more) solvation sites with quadrupole splittings of opposite signs The deuterium spectra of the neat deuterium labelled cis diol 2e exhibit two different signals due to the two deuterons which are located at the axial and equatorial hydroxyl groups. This indicates that there is no fast intra- or intermolecular exchange of the hydroxyl hydrogens. The overall quadrupole splittings of the hydroxyl deuterons in this compound are highly reduced compared to their static values and this is interpreted in terms of motional modes involving both reorientation of the hydroxyl deuterons about their C-O axis and overall reorientation of the molecules (or pairs of molecules) around the columnar axes. The corresponding spectra of the neat deuteriated trans diol 3e exhibit a single spectrum indicating that both hydroxyl deuterons in this compound are equivalent, or very nearly so. Within the mesophase region the spectrum undergoes gradual changes due to the increase in the molecular mobility, but the overall motional narrowing is less than in the cis isomer 2e. Apparently due to stronger hydrogen bonding in the trans isomer 3e the precession of the hydroxyl groups is hindered and a fast molecular reorientation is only possible at high temperatures.     

Static periodic distortion above bend Freedericksz transition in nematics

The linearized mathematical model developed by Allender, Hornreich and Johnson [1987, Phys. Rev. Lett., 59, 2654], for explaining the appearance of the magnetic field induced stripe phase (SP) above the bend Freedericksz threshold in a nematic close to the smectic transition, is generalized to the case of uniform tilt θ₁ of the nematic director n₀ away from the homeotropic with the field H acting normal to n₀. Calculations of SP threshold and domain wave vector Q are presented for different elastic ratios and tilts θ₁, by exact computation of the ground state homogeneous deformation (HD) under the rigid anchoring hypothesis. Approximate estimates based on energetics, explicitly taking into account the modal symmetry of perturbations, agree well with the results of exact calculations based on the solution of torque equations. For homeotropic alignment (θ₁ = 0) calculations predict that the SP domain width should decrease when the sample is heated away from the smectic transition point; at a given temperature when H is rotated through a small angle with respect to the sample planes the domains should grow wider. These points can be verified experimentally. It is also shown that for sufficiently high initial tilt θ₁ away from the homeotropic director alignment, SP may be quenched. Materials, such as nematic polymers, which exhibit static periodic domains (PD) in splay geometry (of the kind discovered by Lonberg and Meyer, 1985, Phys. Rev. Lett., 55, 718) may also show SP for director tilts θ₁ close to the homeotropic. It appears possible to make tentative predictions regarding the effects of weak anchoring and oblique magnetic fields on the SP threshold and domain wave vector.     

On a Possible Mechanism for the Spontaneous Freedericksz Effect

Kaznacheev and Sonin have presented a model to explain the so-called spontaneous Freedericksz transition in nematic liquid crystals (1983, Sov. Phys. solid Sr, 25, 528; 1984, Ibid, 26, 486). A surface polarization, coupled with the negative anisotropy of the nematic, turns the two homeotropic anchoring plates into planar anchoring plates. We show that this model, correctly solved, cannot explain the observed critical thickness. The spontaneous Freedericksz transition is in fact the surface instability of a hybrid cell with weak planar anchoring.     

Copper-sulfide cluster assembled architecture via in situ reaction

A new copper-thiolate cluster assembled framework [Cu₂(μ₄-SCH₃)Cl]_n (1), has been solvothermally synthesized through in situ reaction viz., in situ ligand generation and metal reduction. Compound 1 represents the first 3D framework based on Atlas-sphere functionalized by single μ₂-Cl^- groups. DOS calculation reveals the interaction of electronic structures. It is found that the HOMO is mainly distributed on Cl, Cu and S bonding orbitals, while the LUMO is dominated by Cu-Cl antibonding orbitals.     

吡啶基离子液体[C_6py][DCA]热力学性质及利用新E?tv?s方程预测其表面张力

制备了吡啶类离子液体N-己基吡啶二氰胺盐[C_6py][DCA],并用核磁共振氢谱(~1H NMR)、核磁共振碳谱(~(13)C NMR)、差热扫描量热(DSC)、傅里叶变换红外(FT-IR)光谱对其进行表征。在288.15–338.15 K温度范围内,采用标准加入法,测定其密度(ρ)、表面张力(γ)和折光率(n_D)。在测得的实验数据的基础上,得到了离子液体[C_6py][DCA]的分子体积(V_m)、表面能(E_a)、摩尔极化度(R_m)和极化率(α_p)。结果显示E_a、R_m和α_p几乎不随温度的变化而发生改变。本文还提出了摩尔表面Gibbs自由能(g_s)的概念,并改进了E?tv?s方程。同时还计算了gs、临界温度(T_c)和E?tv?s方程经验参数(kE),并预测了离子液体[C_6py][DCA]的表面张力,预测值与实验值具有较好的一致性。     

Ferroelectric liquid crystals induced by atropisomeric biphenyl dopants: the effect of chiral perturbations on achiral dopants

The addition of the achiral biphenyl dopant 2,2',6,6'-tetramethyl-4,4'-bis(4-n-nonyloxybenzoyloxy)biphenyl (3) or its dithionoester or dithioester analogue (4, 5) to a 4 mol % mixture of the atropisomeric biphenyl dopant (R)-2,2',6,6'-tetramethyl-3,3'-dinitro-4,4'-bis(4-n-nonyloxybenzoyloxy)biphenyl, (R)-1, in the phenylpyrimidine SmC host PhP1 produces a significant amplification of the spontaneous polarization induced by (R)-1. This amplification may be due to a chiral perturbation by (R)-1 which causes a shift in the equilibrium between enantiomeric conformations of the achiral dopant. The degree of polarization amplification afforded by the achiral dopant, as expressed by the polarization amplification factor PAF, varies with the nature of the linking group. This may be ascribed to different rotational distributions of the core transverse dipole moments relative to the polar axis of the SmC* phase and/or to differences in lateral bulk of the polar linking groups. The latter may affect the degree of chiral molecular recognition achieved by 3-5 in the binding site of the SmC* phase.     

Assembly of Two Isostructural Metal-organic Frameworks Based on Hetero-N,O Donor Ligand for Detecting Nitro Explosives

Two isostructural metal-organic frameworks,[NO3][M3(H2O)3O(TBA)3]-2DMF-6H2O(1 and 2)[M=In and Fe, H2TBA=4-(1H-tetrazol-5-yl)-benzoic acid], have been successfully synthesized. Compounds 1 and 2 have three-dimensional structures bridged via the typical 6-connected tri-nuclear cluster units M3O(COO)6 and linear linker H2TBA. The whole 3D framework possesses a 6-connected acs topology. Notably, by the fluorescence technique, compound 1 can detect nitro explosives through fluorescence quenching effect, especially for 2,4,6-trinitrophenol(TNP, Ksv=3.64×10^4 L/mol). Furthermore, the fluorescence spectrum red shifts as the number of NO2 group increases. Based on the aforementioned consideration, compound 1 can be considered as a potential luminescent probe for the detection of TNP.     

醚基功能化离子液体[MOEMIm]Cl和[EOEMIm]Cl热力学性质

通过核磁共振氢谱,核磁共振碳谱,元素分析和热重分析对醚基功能化的离子液体[MOEMIm]Cl和[EOEMIm]Cl进行了表征。在温度范围T=288.15–328.15 K内,测定了离子液体[MOEMIm]Cl和[EOEMIm]Cl的密度(ρ)、表面张力(γ)和折光率(nD)。根据这些实验数据,讨论并计算了离子液体[MOEMIm]Cl和[EOEMIm]Cl的体积性质。计算出离子液体[MOEMIm]Cl和[EOEMIm]Cl的摩尔表面吉布斯自由能(gs)、摩尔表面熵(s)、摩尔表面焓(h)、摩尔极化度(Rm)和摩尔极化率(αp),h均近似为一个常数说明这两种离子液体从内部到表面的过程是一个等库仑过程,同时这两种离子液体的Rm和αp均与温度无关。本文还用摩尔表面Gibbs自由能改进Lorentz-Lorenz方程并预测离子液体表面张力,预测值与实验值高度相关。     

Mesogenic behaviour of (4-alkoxybenzylideneamino)bromobenzene, (4-alkoxybenzylideneamino)benzenethiols, and thiolatonickel complexes of the thiols

The synthesis, characterization and mesogenic properties of Schiff base compounds arising from the reaction of 4-alkoxybenzaldehydes with 4-aminothiophenol or 4-bromoaniline are described. Whereas the Schiff base thiol with two benzene rings in the molecule, HSC₆H₄NC(H)C₆H₄OC₁₆H₃₃ (2), is non-mesogenic, the bromo analogue, BrC₆H₄NC(H)C₆H₄OC₁₆H₃₃ (3), is mesogenic. The introduction of a third benzene ring into the molecular architecture of 2 and 3 produced thiol- and bromo-Schiff base compounds, HSC₆H₄NC(H)C₆H₄OC(O)C₆H₄OC₁₆H₃₃ and BrC₆H₄NC(H)C₆H₄OC(O)C₆H₄OC₁₆H₃₃, respectively, that are both mesogenic. The thiol compounds react with nickelocene to form [(η ⁵-C₅H₅)Ni(μ ₂-SC₆H₄NC(H)C₆H₄OC₁₆H₃₃)]₂ and [(η ⁵-C₅H₅)Ni(μ ₂-SC₆H₄NC(H)C₆H₄OC(O)-C₆H₄OC₁₆H₃₃)]₂, but the nickel complexes are not mesogenic.     

Ca掺杂的CeO2模型催化剂的形貌和电子结构及其与CO2分子的相互作用

利用扫描隧道显微镜、X射线光电子能谱和同步辐射光电子能谱研究了CeO₂(111),部分还原的CeO_2-x(111) (0＜x＜0.5)以及Ca掺杂的CeO₂模型催化剂的形貌、电子结构以及它们与CO₂分子间的相互作用。CeO₂(111)和部分还原的CeO_2-x(111)薄膜外延生长于Cu(111)单晶表面。不同Ca掺杂的CeO₂薄膜是通过在CeO₂(111)薄膜表面室温物理沉积金属Ca及随后真空退火到不同温度而得到的。不同的制备过程导致样品具有不同的表面组成,化学态和结构。CO₂吸附到CeO₂和部分还原的CeO_2-x表面后导致表面羧酸盐的形成。此外,相比于CeO₂表面,羧酸盐物种更易在部分还原的CeO_2-x表面生成,而且更加稳定。而在Ca掺杂的氧化铈薄膜表面,Ca²⁺离子的存在有利于CO₂的吸附,且探测到碳酸盐物种的形成。     

Ag3PO4微晶表面热力学函数的温度及形貌效应

在室温下采用离子交换法制备了四足状、 立方体状和十二面体状Ag₃PO₄微晶及Ag₃PO₄块体, 并进行了表征. 以Ag₃PO₄微/纳米和块体材料热力学性质的区别为基础, 结合化学热力学理论和热动力学基本原理, 导出摩尔表面热力学关系式. 在此基础上, 采用原位微量热技术获取Ag₃PO₄的化学反应动力学信息和表面热力学函数, 讨论了形貌和温度对表面热力学性质变化的影响. 结果表明, 四足状Ag₃PO₄的摩尔表面焓(\begin{array}{c}{H}_m^s\end{array})、 摩尔表面Gibbs自由能(\begin{array}{c}{G}_m^s\end{array})和摩尔表面熵(\begin{array}{c}{S}_m^s\end{array})最大, 立方体状次之, 十二面体状最小; \begin{array}{c}{H}_m^s\end{array}和\begin{array}{c}{S}_m^s\end{array}随温度的升高而增大, \begin{array}{c}{G}_m^s\end{array}则随温度的升高而减小.     

Two New Borates Built by Different Types of {B9} Cluster Units

Two new belt-like borates Na₄[B₉O₁₄(OH)₃]·0.5H₂O(1) and Na₅[B₉O₁₄(OH)₄](2) have been synthesized under solvothermal conditions. Both compounds contain unprecedented B₉O₁₆(OH)_n^(n+5)-[n=3(1), 4(2)] clusters, which are constructed from four B₃O₃ rings via three BO₄ tetrahedra. Compound 1 exhibits a rare 1D belt with two types of 8-membered ring(MR) windows based on B₉O₁₆(OH)₃^8- clusters. Compound 2 features two different 1D belts built by different B₉O₁₆(OH)₄^9- units, which is first discovered in borate family. UV-Vis diffuse reflectance spectra reveal that compounds 1 and 2 have the cut-off edges below 190 nm, indicating that they may have potential application in deep UV(DUV) region.     

Adsorption of bacterial surface polysaccharides on mineral oxides is mediated by hydrogen bonds

Adhesion of bacterial cells to solid surfaces is often largely affected by bacterial surface polymers. In this study, we investigated the adsorption of three different O-antigens isolated from bacterial lipopolysaccharides on TiO₂, Al₂O₃, and SiO₂. The O-antigens of Escherichia coli 08 DSM 46243 and Citrobacter freundii PCM 1487 had high affinity for TiO₂ and low affinity for Al₂O₃, whereas the O-antigens of Stenotrophomonas maltophilia 70401 had low affinities for both surfaces. Adsorption on SiO₂ was low for all polysaccharides. The dependence of the adsorption on the molecular mass of polysaccharides was investigated with dextrans of various chain lengths. The affinity increased with the molecular mass. The affinity of the dextrans was reduced compared with the O-antigen of E. coli, which had similar chemical composition and molecular mass. The adsorption of the E. coli and C. freundii O-antigens on Al₂O₃ and TiO₂ was irreversible, whereas for the S. maltophilia O-antigen it was partially reversible. The reversibility of dextran adsorption decreased with increasing molecular mass.

Infrared spectroscopy showed that all bacterial O-antigens and the dextrans formed hydrogen bonds with surface hydroxyl groups or interacted with surface-bound water of TiO₂, Al₂O₃, and SiO₂. A concentration-dependent mechanism of adsorption was observed with TiO₂. At low polysaccharide concentrations, the surface water molecules ware replaced by the polysaccharides, and at increased concentration the surface hydroxyl groups were involved in the formation of hydrogen bonds. At higher surface coverages, the adsorbed polysaccharides formed loops between the few adsorbed units.     

Structural characterization of the smectic polymorphism of chiral liquid crystalline polysiloxanes containing biphenyl mesogens

A structural characterization of chiral side chain siloxanes with different average degrees of polymerization, DP_n, was performed by X-ray diffraction experiments on powder and oriented fibre specimens. Polymers (DP_n = 35) and oligomers (DP_n = 4) contained the 4,4'-biphenylene unit with either an (S)-2-methylbutoxy (An, Bn) or an (S)-2-chloro-3-methylbutanoyloxy substituent (Cll). The spacer segment connected to the siloxane backbone had a variable number, n, of methylene groups (n = 5, 8, or 11). Independent of the spacer length and the chiral tail nature, the polysiloxanes underwent the same sequence of phases: C-S_F1 (or S_I1)-S_C1-S_A1-I, whereas in the oligosiloxanes the sequence C-S_B1-S_A1-I (B11) or C-S_F1-S_C1-I (B5) occurred. The influence of the structure of the polysiloxanes on the formation of the smectic (tilted or orthogonal) mesophases was elucidated. The rather large number of reflections (three or four) detected in the X-ray patterns at low angles, allowed a drawing of the projection of the electron density profiles along the layer normal, p(z), and deduction of the most physically acceptable electron density profiles from among the numerous possibilities for each smectic phase. The electron density profiles were in agreement with monolayer smectic phases presenting a microphase separation between the siloxane backbones and the side chains, so constraining the polymer backbones within a thin layer.