Investigation of a Twisted Phase between the Cholesteric and the Smectic A Phase

In a ternary mixture of two liquid crystals and a non-mesomorphic chiral dopant an intermediate state with an unusual texture was found between the cholesteric and the S_A phase which could be identified as a separate twisted mesophase. The reflection wavelength of this mesophase does not change with temperature whereas the transmission of unpolarized light decreases from 50 to 20%. The experimental findings point to the existence of a twisted grain boundary phase.     

Two Crystal Forms of 4-{(2<Emphasis Type="Italic">E</Emphasis>)-2-[1-(4-Methoxyphenyl)ethylidene] hydrazinyl}-8-(trifluoromethyl)quinoline

Abstract  

The Schiff base, 4-{(2E)-2-[1-(4-methoxyphenyl)ethylidene] hydrazinyl}-8-(trifluoromethyl)quinoline, crystallizes in two polymorphic forms depending on the solvent. One of these forms is monoclinic (1M), space group P2₁/c with a = 10.2906(10) ?, b = 8.9211(7) ?, c = 18.4838(15), β = 97.271(8)°, and the other is orthorhombic (1O), space group Pbca, unit-cell parameters: a = 13.6485(12) ?, b = 9.0588(9) ?, c = 27.400(2) ?. The molecules in either crystalline form have similar bond lengths and angles, but one is nearly planar while the other has a significant twist. In monoclinic form the dihedral angle between terminal ring planes is 17.26(8)° while in the orthorhombic one it is 26.11(5)°, and in this latter case the central chain is almost coplanar with the quinoline ring system while in the former these two planes are significantly twisted. The crystal structures of both forms are determined by the interplay of van der Waals forces and weak directional interactions C–H···F, π···π stacking, and—in the case of 1M—short intermolecular C–F···N contact. The crystals of 1M decomposes slowly into the powder while the other form is stable. The powder diffraction pattern of the product of decomposition of 1M is similar to that calculated for 1O. This suggests that the decomposition is a consequence of the phase transition of the less stable monoclinic into more stable orthorhombic form.     

A pure reentrant cholesteric phase

Abstract

An optically active derivative of p-cyanobiphenyl exhibits a stable reentrant cholesteric phase with the seuqnce: K N?S_A N?I.     

Market Trends for Flat Panel Displays

Abstract

Arecent report from Stanford Resources entitled ‘Flat Panel Monitor Market Trends 1988’ presents a realistic forecast for the FPD market, which is expected to reach a shipment value of $4 billion in the year 2000. The Flat Panel Display market covers active matrix twisted nematic displays (TFT-LCD) and matrix-addressed super-twisted nematic displays (STN-LCD), and the following are highlights from the market analysis and forecasts.     

A BODIPY-based highly emissive dye with thiophene-based branch harvesting the light

ABSTRACT

A novel BODIPY-based dye with highly emissive character was configured by Sonogashira coupling and routinely characterized by NMR and MS technology. The emission of dye was investigated in solution/film/solid and shows intensive emission. In solution, the emission peak appeared around 510 nm with little influence by the polar environment. The terthiophene plays an effective antenna effect, harvesting the light and transferring the energy to BODIPY. The pseudo Stoke's shift enlarged to ～170 nm in solution. In film, the emission peak shifted to 563 nm in polycarbonate matrix. And it shifted further to 585 nm in solid due to the highly twisted structure, which avoided closely regular-tight packing. The dye rendered an intense fluorescence, good optothermal stability, and high fluorescence quantum yield (0.55). The solid emission showed highly red emission with Commission Internationale de L'Eclairage (CIE) coordinates of (X = 0.69, Y = 0.31). Thus, the synthesized dye is idea candidate for emitting materials.     

Structure of Three Related Diphosphorus Ligands: Highlighting the Significance of the Backbone

Abstract  

The three compounds contained in this report—4,6-bis(diphenylphosphino)-10,10-dimethylphenoxasilin (sixantphos), 1; 4,5-bis(diphenylphosphino)-9-isopropylidenexanthene, (isopropxantphos) 2 and bis-(2-diphenylphosphino)-p-tolyl) ether (PTEphos) 3, all contain a common ether-linked diphenylphosphino backbone. These structures are of interest with respect to the intra-molecular P···P distance which is 3.884(2), 4.104(2) and 5.151(2) ? for 1, 2 and 3 respectively. The differences in the P···P distances are as a result of the variations in the backbones. Structure 1 shows a significant roof-like bending of the backbone along the axis of planarity involving the oxygen and Si donor atoms. Compound 2 is also folded with a larger dihedral angle of 35.85(2)° as compared to 24.14(2)° found in 1. The backbone in structure 3 is significantly bent and twisted with a dihedral angle of 67.34(2)°. These data show the effect on the intra-molecular P···P distance of varying the backbone of three xantphos-type ligands, with respect to the nature of the heterocycle donor 1, the substituent on the donor 2 and total loss of xanthene character 3.     

High-temperature fluorescence of low- and high concentration aqueous ATP solution

Abstract

The results of an experimental study of luminescence of an aqueous solution of adenosine triphosphate (ATP) at room temperature are presented. High-temperature fluorescence of low- and high-concentrated solution was experimentally detected and analyzed. The shape of the fluorescence spectrum, the excited state lifetime and the temperature behavior of the emission intensity indicate the formation in the high-concentrated solution of rather stable dimer-like complexes, which can form excimer states.     

Low-Frequency Dielectric Relaxations in Nematics and Dual-Frequency Addressing of Field Effects

Abstract

Novel low threshold nematic mixtures are presented exhibiting very low dielectric crossover frequencies f_c ? 1 kHz at 20°C and unusually large, low- as well as high-frequency dielectric anisotropies ΔEL > 4 and ΔEH < 4 respectively. ΔEL and ΔEH are shown to be independently adjustable. The frequency and temperature dependence of the dielectric constants as well as the optical, elastic and viscous material constants are measured. Approximations are derived which quantitatively describe the influence of the LC material properties on the static electro-optical performance of dual-frequency addressed twisted nematic displays. It is shown that the number of multiplexable lines of dual-frequency addressed TN-LCDs comprising the new materials can be increased by more than a factor of 30 compared with conventional addressing. Moreover, very short turn-off times are reported.     

Unusual Glassy Smectic-G Liquid Crystal: Heat Capacity of N-p-n-Pentyloxybenzylidene-p'-n-butylaniline between 11 and 393 K

Abstract

The heat capacities of the title compound (C₃H₁₁,O—C₆H₄,- CH=N—C₆H₄,—C₄H₉, abbreviation 5O ? 4) with a purity of 99.92 mole percent have been measured with an adiabatic-type calorimeter between 11 and 393 K. The transition temperature and the enthalpy and entropy of phase transition for stable crystal → S_G, S_G → N and N → isotropic liquid were T _c = 299.69 K/ΔH = 22.68 kJ mol^?1/ΔS = 75.70 JK^?1 mol^?1, 325.72/7.11/21.79 and 342.48/1.78/5.22, respectively. The crystal which melts at 285.5 K is a metastable modification. The S_A phase hitherto reported in between S_G and N does not exist. The glassy So state was realized by rapid cooling of the specimen from the So phase. The molar enthalpy of the glassy S_G state at 0 K was by (10.1±0.1) kJ mol^?1 higher than that of the stable crystalline state and the residual entropy of the glassy state was (9.40±0.83) JK^?1 mol^?1. The relaxational heat-capacity anomaly was observed from as low as 100 K and double glass transition phenomenon occurred around 200 K; a quite unusual phenomenon which has never been observed for the glassy states of nematic and cholesteric liquid crystals. The present results give a fair evidence that the unusual glass transition phenomenon previously found for the S_G state of 6O?4 (a homologous compound) is not exceptional at all but common to the smectic glasses; at least common to the glassy S_G states. Two possible origins responsible for the double glass transitions have been discussed.     

From Chiral Molecules to Chiral Liquid Crystal Phases

Abstract

During the last decade, the topic of chirality and symmetry in physical sciences has become extremely important, particularly as nature itself is often described as being “handed” or chiral. In liquid crystalline systems many important properties are known to be related to chirality, for instance chirality is reflected in helical structures, in special cases of strongly twisted systems novel frustrated phases may appear such as Blue phases and Twist Grain Boundary phases. In addition, many modern high technology applications, such as ferroelectric displays depend entirely on the presence of chirality in the liquid-crystalline materialsemployed.     

Crystal structure of N,N ′-bis(cyclohexyl)-1-(N,N-dihexylamino)perylene-3,4:9,10-bis(dicarboximide)

An asymmetric dialkylamino-substituted perylene bisimide (1), N,N′-bis(cyclohexyl)-1-(N,N-dihexylamino)perylene-3,4:9,10-bis(dicarboximide), was synthesized and characterized by single-crystal X-ray diffraction. The crystal belongs to triclinic, space group P–1, with a = 9.8924(6), b = 14.6338(10), c = 15.6221(10) Å, α= 105.098(3)°, β = 103.386(2)°, γ = 107.772(3)°, and Z = 2. The central perylene core of 1 is twisted with dihedral angles of 14.9(3)° and 11.6(3)°; this twist configuration induces the axial chirality in this family of perylene bisimide dyes. In the crystal structure, the intermolecular C–H···O interaction links a pair of molecules into a cyclic centrosymmetric dimer that is connected to one another via the intermolecular π–π stacking, so linking the molecules into a continuous one-dimensional framework along the [100] direction.     

X-Ray Structure of the Key Synthetic Intermediate of a Cancer-Related Sialyl-Tn Antigen Analogue

Abstract  

We report herein the synthesis and the X-ray crystal structure of 2-azido-2-deoxy-3,4-O-isopropylidene-α-d-galactopyranosyl-N-oxyphthalimide 3 which is the key-precursor of a cancer-related STn antigen analogue 5. Compound 3 crystallizes from a mixture of dichloromethane/pentane as colorless orthorhombic needles in P2 ₁ 2 ₁ 2 space group with the following cell parameters: a = 14.039(2) ?; b = 16.574(3) ?; c = 8.038(1) ?. The hexapyranose ring of 3 adopts a twisted boat according to the Cremer and Pople puckering parameters (Cremer and Pople, J Am Chem Soc 97:1354, 1975) whereas the structure determination of the corresponding deprotected intermediate 4 (orthorombic colorless prisms, P2 ₁ 2 ₁ 2 ₁ space group, a = 4.927(3) ?; b = 13.423(2) ?; c = 22.744(3) ?) has revealed a quasi perfect chair.     

Synthesis,crystal and molecular structures of 1,8-diaza-11,14-dioxacyclohexadeca-2,7-dione and 1,10-diaza-4,7-dioxacyclohexadeca-2,9-dione

1,8-Diaza-11,14-dioxacyclohexadeca-2,7-dione (3) has been synthesized under high-pressure conditions, whereas 1,10-diaza-4,7-dioxacyclohexadeca-2,9-dione (6) has been obtained under thermal conditions. Both compounds have been investigated in the solid state and in solution by X-ray structural and NMR methods, respectively. The crystals of3 are orthorhombic, space groupPbca; the crystals of6 are triclinic, space groupP¯1. Both structures were solved by direct methods, and refined by a full-matrix, least-squares procedure giving for3 R=0.045 and for 6R=0.056 (R _w =0.065). From the NMR investigations in solution a twofold symmetry of both molecules (probably in intermediate conformations) is suggested; no such symmetry was found in crystalline state. The structure of6 exhibits a positional disorder of one O-heteroatoms with the population ratio 0.510.49. The arrangement of the macroring with respect to the carbonyl groups was found to betransoid in3 andcisoid in6.     

A novel stable CuI complex based on an unconjugated bisanthryl-tethered diimine ligand with tri-coordinate mode

The first air-stable mononuclear Cu^I complex (1) based on an unconjugated bisanthryl-tethered diimine ligand has been synthesized and characterized by elemental analysis, ESI-MS, UV-vis, FT-IR spectra and TGA analysis. X-ray diffraction analysis at room temperature reveals that complex 1 crystallizes in a monoclinic system, space group P2₁/c with a=15.611(3) ?, b=24.412 (5) ?, c=15.430 (6) ?, β=114.49 (3)°, V=5351.3 (19) ?³, ρ _calc=1.359 g cm⁻³, μ=0.472 mm⁻¹ and Z=4. The crystal structure of 1 features a mononuclear tricoordinated complex with a distorted triagonal planar geometry. The Cu^I center is coordinated to three imine N atoms of two Schiff base ligands, while the remaining one imine N atom keeps uncoordinated. UV-vis absorption and emission spectra indicate that the complexation of metal ion has slight influence on the electronic structure of the ligand. TGA analysis confirms that complex 1 is stable up to 253°C.Supplementary materials Crystallographic data reported in this paper have been deposited with Cambridge Crystallographic Data center (CCDC no.282672). Copies of the data can be obtained free of charge from www.ccdc.cam.ac.uk/conts/retrieving.html (or from the Cambridge Crystallographic Data Center, 12, Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223 336033; or deposit@ccdc. cam. ac.uk).     

A fast-switching vertically-aligned liquid crystal device based on a multi-functional mesogenic photocrosslinker

Abstract

A vertically-aligned liquid crystal (LC) device with fast-switching LC molecules and excellent electro-optical properties is proposed. The proposed method employs a mixture of a polyimide to achieve the desired vertical alignment, and a mesogenic photocrosslinker to obtain the fast LC response. More specifically, the photocrosslinkers were photopolymerized by UV irradiation under an electric field to pre-tilt the LC molecules. In addition, upon increasing the number of functional groups in the photocrosslinker, faster switching properties were exhibited due to enhanced pre-tilting. Following UV irradiation, the proposed system also exhibited stable homeotropic alignment properties similar to those of conventional polyimides.     

Dynamics of Intercalated Water Molecules in Synthetic Layered Silicates

Abstract

Diffusional motions of water molecules in a synthetic fluorinated layered silicate have been studied by neutron scattering. Motions in a one-water-layer hydration state are slower than in those in a two-water-layer hydration state. Good fits to the data were obtained with the Kohlrausch-Williams-Watt lineshape that is often applied to disordered systems.     

Crystal and molecular structures of 1-(2-methyloxycarbonylo-propan-2-ylamino)-3-(1-naphthyloxy) propan-2-ol hydrochloride (1) (C18H24NO4Cl) and 1-(2-methylcarbamoylpropan-2-ylamino)-3-(1-naphthyloxy) propan-2-ol (2) (C18H24N2O3)

The crystal structures of two new-adrenergic antagonists, derivatives of propranolol, are reported in this paper. The space groups and unit-cell parameters are: compound1 (C₁₈H₂₄NO₄Cl), monoclinic,P2₁,a=7.215(1),b=8.591(1),c=15.017(1)Å,=95.64(1)°; compound2 (C₁₈H₂₄N₂O₃), monoclinic,P2₁/c,a=10.218(3),b=21.616(5),c=8.124(2)Å,=101.28(2)°. The structures were solved with direct methods and refined by full-matrix least-squares techniques toR indices of 0.036 and 0.066, respectively. The molecule of compound1 has an extended external chain, and thus its structure is linear, whereas the molecule of compound2 is compact, and its external chain is twisted in a characteristic way, as is the case of peptides.     

Synthesis and crystal structure of oxonitrate complexes Cs[VO2(NO3)2], Cs[MoO2(NO3)3], and MoO2(NO3)2

Cs[VO₂(NO₃)₂] (I), MoO₂(NO₃)₂ (II), and Cs[MoO₂(NO₃)₃] (III) complexes have been obtained by crystallization from nitric solutions and studied by single-crystal X-ray diffraction. Complexes I and II contain infinite zigzag chains of similar compositions, [VO₂(NO₃)₂]⁻ and [MoO₂(NO₃)₂], in which V and Mo atoms form, respectively, trigonal- and pentagonal-bipyramidal polyhedra. Each of these polyhedrons also contains one terminal and two bridge O atoms and two terminal NO₃ groups which are monodentate and bidentate in complexes I and II, respectively. Complex III has an island structure and consists of Cs⁺ cations and [MoO₂(NO₃)₃]⁻ anions, in which the Mo atom is surrounded by one bidentate NO₃ group and two monodentate NO₃ groups and two terminal O atoms in the cis-positions; oxygen atoms form a polyhedron in the form of distorted octahedron. According to the ab initio calculation of isolated MoO₂(NO₃)₂ molecules in the gas phase and solution, the coordination environment of the Mo atom, similarly to the Cr(VI) atom in CrO₂(NO₃)₂, is formed by two bidentate nitrate groups and two terminal O atoms (polyhedron- twisted trigonal prism).     

X-ray crystal structure of the 1:1 dimethylpicric acid–acenaphthene complex

The dimethylpicric acid–acenaphthene complex is orthorhombic, space group P2₁2₁2₁; at 24° a = 7.3685(1), b = 15.4159(1), c = 16.1296(3) Å, D _x = 1.491(2) g cm^–3, V = 1832.19(4) ų, Z = 4. The phenolic OH group in the dimethylpicric acid is intramolecularly hydrogen bonded to one of the ortho nitro groups with an OO distance of 2.500(2) Å. This nitro group is twisted out of the plane of the benzene ring by 8.2°; the twist angles of the other nitro groups are 52.6 and 83.5°. The acenaphthene molecule deviates slightly from planarity as a consequence of the torsion angle at CH ₂-CH ₂ being 1.8 rather then 0°. The molecules pack in stacks of alternating picric acid and acenaphthene molecules. Each stack is surrounded by a close-packed arrangement of six other stacks. The acenaphthene molecules are 2.7° away from being parallel to the benzene ring in the picric acid. The distances from the benzene ring to the acenaphthene carbon atoms range from 3.26 to 3.49 Å on one side of the ring and from 3.30 to 3.54 Å on the other.     

Synthesis and Characterization of Two Pb(II) Complexes of 2,2′-dihydroxy,Dimethoxy-1,1′-binaphthyl-3,3′-dicarboxylic Acid

Two new complexes {[Pb(L¹)(DMSO)₂(H₂O)]·DMF}_n (1, L¹ = 2,2′-dihydroxy-l,l′-dinaphthyl-3,3′-dicarboxylate) and {[Pb(L²)(DMS O)·DMSO}_n (2, L² = 2,2′-dimethoxy-l,l′-dinaphthyl-3,3′-dicarboxylate) have been synthesized under mild conditions and structurally characterized. Crystal structural analysis reveals that complex 1 adopts a 1D infinite chain structure which forms 2D sheet by hydrogen bonds interactions. Complex 2 possesses a 2D sheet structure, which was further assembled into a 3D supramolecular network through the π-π weak interactions. IR spectra indicates the carboxyl group coordinates with the Pb²⁺ ion. TGA shows that complex 2 is highly thermally stable up to 120°C.