Liquid Crystalline Phases in the Homologous Series of Terephthalylidene-BIS-[4-n-Alkylanilines]

The liquid crystalline polymorphism in the homologous series of terphthalylidene-bis-4-n-alkylanilines was investigated by miscibility experiments. The variants of polymorphism found in the members with carbon atoms n = 3 to n = 10 in the alkyl chains can be derived from a variant HGFICA Nthrough the absence of one or several phases. Beside the known phases H, G, F, C, A, and N, the new phase type 1 was found. The results are discussed in connection with investigations on structure.     

Thermal Microscopy and DSC Studies of 4-[4-n-pentyloxybenzylideneamino] Azobenzene

Phase transition studies of the liquid crystal, 4-[4-n-pentyloxybenzylidene–amino]–azobenzene (PBAAB) have been investigated by thermal microscopy and Differential Scanning Calorimetry (DSC) studies. From these studies it is confirmed that the compound, PBAAB exhibits nematic, smectic A and smectic B phases. The textures exhibited by different phases are presented. The enthalpies and entropies at various phase transitions are also reported.     

Calorimetric investigations of 2-[4-n-alkylphenyl]-5-[4-n-alkyloxyphenyl]-pyrimidines

We investigated temperatures and enthalpies of the phase transitions by means of the calorimeter DSC-2. The kinetics of polymorphic transitions in the solid state, the pretransitional behaviour in the liquid crystalline phases and the transition enthalpies, ranging from 3 J/mol up to 50 kJ/mol, in relation to the occurrence of the liquid crystalline phase types S_G, S_F, S_C, S_A, and N are points of discussion.     

X-Ray Diffraction Studies of Liquid Crystalline Polymers

Thermotropic liquid crystalline copolyesters display an ordered fluid phase at elevated temperatures which permits the development of unusually high orientation at ambient temperatures. The transition which occurs upon cooling the high temperature nematic liquid crystalline phase very rapidly (e.g. fiber spinning) results in a polymeric glass with nematic structural order. Annealing increases structural order from the nematic glass toward ideal three dimensional crystalline order. Precision X-ray diffractometry has been used to directly observe changes in structural correlations which occur with annealing. Structural transitions range in character in these copolyesters from no change upon annealing to a transition from fully two dimensional to fully three dimensional structural order. Increased three dimensional order also results in substantially increased first order character of the high temperature phase transition. The chemical structure of co-monomers determines, in part, the final degree of dimensionality.     

Optical Rotatory Dispersion Measurements of the Liquid Crystalline Blue Phases in Thick Layers

The results of optical rotatory dispersion (ORD) measurements in liquid crystalline blue phases (BP) are reported for pure compounds and mixtures. They have been performed on polycrystalline samples (thick layers). Two features distinguish their spectra from those obtained from liquid single crystals:

(1) The magnitude of the rotation is much smaller, and

(2) no sharp anomalous ORD region is present.

The spectra possess a weak, broad anomalous region. Their sign and wavelength dependence follows the sense and pitch of the cholesteric helix. ORD experiments with mixtures of the same cholesteric esters with a nematic substance yield results typical of well oriented samples. The spectra exhibit larger rotation angles and a significantly smaller anomalous region.     

4-(E)-2-[3-(3-[(E)-2-(4-cyanophenyl)-1-diazenyl]perhydrobenzo[d]imidazol-1-ylmethyl)perhydrobenzo[d]imidazol-1-yl]-1-diazenylbenzonitrile: X-ray crystal structure

4-(E)-2-[3-(3-[(E)-2-(4-Cyanophenyl)-1-diazenyl]perhydrobenzo[d]imidazol-1-ylmethyl) perhydrobenzo[d]imidazol-1-yl]-1-diazenylbenzonitrile (1) has been synthesized by reac- tion of p-cyanobenzene diazonium chloride with a mixture of formaldehyde and trans-1,2-cyclohexanediamine. The crystal structure has been determined by single crystal X-ray diffraction analysis. The bis-triazene (1) does not adopt a folded conformation, unlike previously studied ethylenediamine analogues, and there is no indication of -stacking in the crystal packing. The dominant interaction between molecules is the van der Waal's attraction between cyclohexane rings. This result establishes the structure of the product of this diazonium coupling reaction as the 1-(1-imidazolidinylmethyl)imidazolidine derivative and not the alternate tetraazabicyclo[4.4.1]undecane derivative. Crystal data: 1 C₂₉H₃₄N₁₀, orthorhombic, space group Pbca, a = 17.946(1), b = 13.106(1), c = 24.108(1) Å, V = 5670.6(3) ų, for Z = 8.     

Rheo-Optical Studies of Liquid Crystalline Solutions of Helical Polypeptides

The shear dependence of structures of liquid crystalline solutions of Poly-γ-benzyl-l-glutamate PBLG in m-cresol was examined in a polarizing microscope using a specially constructed shearing stage and stroboscopic illumination. Three different textures were observed depending on shear rate. The shear rates at which the texture changes occurred correlated well with the changes in sign of the first normal stress difference reported earlier.^1,2 The region of negative first normal stress difference corresponded to a texture consisting of striations perpendicular to shear.

The transverse striations were also observed to develop over a period of seconds or minutes after cessation of shear at rates within the first positive region of N ₁, These striations could be fixed in a dried film by using a volatile helicogenic solvent (1,4-dioxane).

A speculative model is proposed to account for the rheological observations in Refs.^1,2 and the rheo-optical observations reported herein.     

EDA Complexes in Liquid Crystalline Mixed Phases of Novel Compounds with Lateral Dicyanoethenyl Substituents

We synthesized each four members of the new series All compounds are nematic. The dicyanoethenyl derivatives possess strong elecgtron acceptor properties. This is demonstrated by EDA complex formation in two binary systems in which induced smectic phases are lacking.     

Crystal and Molecular Structure of the Smectogen 1-[4-n-heptylbenzoyl]-2-[cyanoacetyl]-hydrazine

The compound 1-[4-n-heptylbenzoyl]-2-[cyanoacetyl]-hydrazine crystallizes in the triclinic space group Pl̄ with two molecules in the unit cell and the lattice parameters a = 4.702, b = 8.640, c = 20.906 Å, a = 97.50, β = 92.79, γ = 100.19°. The structure was solved by direct methods and refined by full-matrix least squares calculations to the final residual value R = 0.039.     

Physical Properties of Liquid Crystalline 5-n-Hexyl-2-(4-n-alkyloxyphenyl)-pyrimidines

In 8 compounds of the substance class 5-n-hexyl-2-(4-n-alkyloxyphenyl)-pyrimidines the clearing temperatures, transition enthalpies, densities and refractive indices were measured. Packing fractions, pressure dependence of the clearing temperatures, polarizabilities, order parameters and the anisotropy of the local field were calculated.     

Enthalpies of Lyotropic Liquid Crystalline Phases. : 2. The Partial Molar Enthalpies of the Lamellar and Hexagonal Phases in the System N-Pentanol-Sodium N-Octanoate-Water

The relative partial molar enthalpies of the components in the system N-pentanol-sodium N-octanoate-water (C₅OH-NaC₈-H₂O) have been determined in the lamellar (D-) and hexagonal (E-) liquid crystalline phases formed in this system at 25°C. The enthalpies are correlated with Bragg spacings and earlier nmr studies. They indicate that (a) the minimum amount of water needed to hydrate the polar groups limits the region of existence of both D- and E-phase towards low water contents, (b) the interaction between -OH and -COO is especially important in stabilizing the D-phase containing large amounts of water, (c) the Bragg spacings and the enthalpies both change their concentration dependence markedly when the maximum amount of water that can be bound by primary hydration of the polar groups and the counter ions in the D-phase is exceeded, (d) enthalpies of transition from one phase to another are small compared to enthalpy changes with composition within the phases; the same holds for Bragg spacings. Hence, the composition of the sample (above all, the mole fraction of NaC₈) is more important than the phase structure in determining these properties. It is obvious that further studies of enthalpies in similar systems can give important information on the factors governing phase stabilities and structural changes within the phases.     

Crystal Structure of 3-[1-(4-Methylphenyl)-9,10-dihydro-4-azaphenanthren-3-yl]benzo[f]coumarin

Crystallography Reports - The crystal structure of the title compound is determined by single crystal X-ray structure analysis. The structure was solved by direct method and refined to a final...     

Observation of Four Crystalline Phases of the One Dimensional Conductor Zn0.81 [Pt(C2O4)2] . 6D2O by Neutron Diffraction

Four different crystalline phases of Zn_0.81[Pt(C₂O₄)₂].6D₂O have been observed and partially characterized by single crystal neutron diffraction measurements. A crystal in the previously reported orthorphombic α-form was pulled along its c-axis at room temperature and was found to transform to a monoclinic β-form. Two new coexisting phases, monoclinic γ-Zn-OP and orthorhombic δ-Zn-OP were found when the sample was cooled to 200 K. Further crystallographic work is necessary in order to establish the detailed nature of the new phases.     

Hydrogen-bis[2-(4-dimethylaminostyryl)-quinoline-1-oxide]dichlorocuprate (I) from X-ray study

X-ray diffraction data on powder and single-crystal samples were used to determine the crystal structure of hydrogen-bis[2-(4-dimethylaminostyryl)-quinoline-1-oxide]dichlorocuprate (I): monoclinic system, sp. gr. P2₁/n, and Z = 2. Two molecules of N oxide of 2-(4-dimethylaminostyryl)quinoline are bound through a hydrogen atom located at the center of symmetry, thus forming a complex cation.     

Thermotropic Liquid Crystalline Compounds with Lateral Long Chain Substituents (VII). X-Ray Studies in 1,4-Bis-(4-n-oetyloxybenzyoloxy)-2-n-alkylbenzenes

X-ray studies in substances with the general formula in the nematic states were performed. The results prove the existence of cybotactic groups despite the fact that the branched substances do not show smectogenic properties. We propose a model for the packing of the molecules, which explains the influence of the lengths of the lateral branches on the structure of the cybotactic groups.     

1-[2-(p-Tolyl)-1-diazenyl]-3-({3-[2-(p-tolyl)-1-diazenyl] perhydrobenzo[d]imidazol-1-yl}methyl)perhydrobenzo[d]imidazole: synthesis,characterization and X-ray crystal structure

1-[2-(p-Tolyl)-1-diazenyl]-3-({3-[2-(p-tolyl)-1-diazenyl]perhydrobenzo[d]imidazol-1-yl}methyl)perhydrobenzo[d]imidazole(1) has been synthesized by reactionof a mixture of 1,2-diaminocyclohexane and formaldehyde withp-toluene diazonium chloride inaqueous solution. The product has been characterized by IR and NMRspectroscopy and elemental analysis. A crystal grown from solution ina mixed solvent system of ethyl acetate and hexanes was analyzed byX-ray crystallography. The solution of the crystal structure of(1) is important in establishing theconnectivity of this molecule and other compounds of similarstructure. The crystal structure of (1) is compared with the previously reportedstructure of the p-cyano analogue(2). Compounds (1) and (2)differ principally in the relative orientation of the heterocyclicrings; in (1), the molecule has adistinct V-shape, whereas compound (2) adopts a more extended conformation.Significant conjugation within the triazene moieties is evident inboth (1) and (2), as manifested in the N465=N andN–N bond lengths. The conjugation is greater in (2) due to the extended conjugation through tothe nitrile group. The title compound (1){C₂₉H₄₀N₈}crystallizes in the monoclinic, space group C2/c, with lattice constants: a = 30.532(6) ?,b =5.9050(12) ?, c= 15.463(3) ?, α = 90°,β = 99.94(3)°, γ = 90°,V =2746.0(10) ?³, Z = 4, D _c =1.209 mg m⁻³,F(000) = 1076, R ₁ = 0.0785,wR ₂= 0.1877.