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71.
72.
Cholesterol-containing liquid crystal dimers with ether linkages between the spacer and mesogenic units 总被引:1,自引:0,他引:1
Antonius T. M. Marcelis Arie Koudijs Zbigniew Karczmarzyk Ernst J. R. Sudh lter 《Liquid crystals》2003,30(11):1357-1364
Three series of chiral liquid crystalline dimers were investigated, having a cholesteryl and a cyanobiphenylyl, butoxybiphenylyl or hexyloxybiphenylyl group connected to a variable alkyl spacer through ether linkages. Their properties were compared with those of the corresponding ester derivatives. The phase behaviour of compounds with ether and ester linkages is comparable, showing N* and SmA phases. The melting points of the compounds with ether linkages are in the same range as those of the ester compounds, but the liquid crystal transition temperatures are lower. The smectic layer spacings and smectic ordering properties are also similar. The cyanobiphenylyl compounds have an interdigitated SmA layer structure, which shows a small odd-even effect with spacer parity. The alkoxybiphenylyl compounds have a monolayer SmA phase for short spacers and an intercalated SmA phase for longer spacers. The selective reflection wavelengths of the chiral nematic phase of the ether compounds are lower than those of the corresponding ester compounds. The transition from N* to interdigitated or monolayer SmA is accompanied by a strong increase in the selective reflection wavelength, indicative of an intermediate TGB phase. This is absent for the transition from N* to intercalated SmA. 相似文献
73.
Non-symmetric bent-core mesogens with one terminal vinyl group 总被引:1,自引:0,他引:1
Remko Achten Arie Koudijs Marcel Giesbers Antonius T. M. Marcelis Ernst J. R. Sudh lter 《Liquid crystals》2005,32(3):277-285
Two series of non-symmetric banana-shaped compounds, both with one alkyl and one alkenyl terminal tail, have been synthesized and studied. Both series were compared with the corresponding series with two saturated terminal alkyl tails. All the compounds have a bent central 1,3-phenylene bis(4-benzoyloxy)benzoate core; their mesophases were characterized by polarizing optical microscopy, differential scanning calorimetry, X-ray diffraction and switching current response experiments. In all four series one of the terminal tails is varied from OC8H17 to OC16H33. The other terminal tails are OC11H23, O(CH2)9CH = CH2, OC10H21 and O(CH2)8CH = CH2. The short-tailed compounds show monotropic or enantiotropic B1 phases and the long-tailed compounds the B2 phase. The introduction of one terminal vinyl group slightly lowers the transition temperatures. The introduction of a second terminal vinyl group further suppresses the liquid crystalline properties. All compounds with B2 phases have layer spacings that suggest a tilt of ∼45° of the bent molecules in the layers, and their switching behaviour is antiferroelectric. 相似文献
74.
Application of an integrated optics (IO) microcavity (MC) for evanescent excitation of two-photon excited fluorescence (TPF) is demonstrated. The MC provides a high local intensity, which is required for the TPF, because of resonant enhancement of the intracavity power and a strong two-dimensional confinement of the guided mode. Numerical estimations show a large increase, by more than a factor of 104 of the TPF intensity at the MC compared to a conventional straight waveguide. This will lead to a significant improvement of the detection limits of UV-absorbing chromophores (down to 10−8 M) when using the MC as a biosensor. Feasibility of TPF excitation using an IO MC is confirmed experimentally for the first time. 相似文献
75.
García Ruano JL Gamboa AE Gutiérrez LG Martín Castro AM Rodríguez Ramos JH Yuste F 《Organic letters》2000,2(6):733-736
A new kind of chiral dienophiles, cyclic vinyl-p-tolylsulfilimines (2a and 2b), were obtained from the corresponding (Z)-sulfinylacrylonitriles with HBF(4) and methanol. The asymmetric Diels-Alder reaction of optically pure 2a with cyclopentadiene under mild thermal or catalyzed conditions afforded only the endo-4a adduct with complete endo and pi-facial selectivities. The ability of the sulfilimine moiety to enhance the dienophilic reactivity of the double bond is similar to that of the sulfinyl group. 相似文献
76.
Xiaojia Li Peter Schramel Zao Wang Peter Grill Ayfer Yediler Antonius Kettrup 《Mikrochimica acta》1996,124(3-4):171-178
A preconcentration method based on third phase extraction has been developed and combined with inductively coupled plasma atomic emission spectrometry (ICP-AES) for determination of Sb, Pb, Tl at trace levels in water samples. The reagents diantipyrylmethane and potassium iodide were applied for complexing Sb, Pb, Tl and producing a third phase extraction system. This third phase system produces relatively large enrichment factors and complete isolation of trace elements from high salt-containing matrices which influence strongly the plasma condition. Experimental parameters of the extraction, such as concentrations of complexing reagents, pH and extraction time have been optimized. Under the selected conditions, this third phase ICP-AES combination procedure gave multielemental detection limits for Sb, Pb, Tl which are superior by an order of magnitude or more to those obtained by ICP-AES alone without preconcentration. Precision of the technique is better than 10% at the 10 g/l level. The accuracy of this approach is demonstrated by its application to tapwater, artificial seawater and reference seawater samples. 相似文献
77.
Molecular structure of 3-(3-oxo-bicyclo[2.2.1]hept-5-en-2-yl)-oxirane-2-carboxylic acid methyl ester
René de Gelder Twan van Enckevort J. M. M. Smits Paul T. Beurskens Jie Zhu A. J. H. Klunder 《Journal of chemical crystallography》1996,26(1):81-84
The crystal and molecular structure of an epoxy ester is described. The structure has been solved by vector search methods and refined by least squares methods toR
1=0.0372 [I>2(I)]. The structure consists of two independent molecules in the asymmetric unit. These molecules are chemically the same. Crystal data: C11H12O4, triclinic, space group
,a=10.324(3),b=10.553(7),c=10.869(5)Å, =61.77(4), =88.64(4), =88.16(6)°,V=1042.7(9)Å3,Z=4. 相似文献
78.
J. M. M. Smits Paul T. Beurskens A. J. H. Klunder M. J. F. M. Crul 《Journal of chemical crystallography》1986,16(5):665-671
The structure of the title compound, C12H16O3, was determined by X-rays.M
r
=208.26, triclinic, space groupP¯1,a=7.802(2),b=8.449(2),c=9.069(1) Å,=90.79(1)°,=105.57(1)°, =106.07(1)°,Z=2,D
x
=1.26 Mg m–3; MoK radiation (graphite crystal monochromator, =0.71069 Å),(MoK)=0.96 cm–1,T=290 K. Final conventionalR-factor=0.046,R
w
=0.067 for 3009 observed reflections and 184 variables. The structure was solved using Patterson methods andDirdif, and the resulting all cis-endo configuration of the alcohol group on C(3) and the ethoxy group on C(5) shows that the stereochemistry of the metal-mediated addition reaction involved is solely determined by steric factors. 相似文献
79.
Remko Achten Arie Koudijs Marcel Giesbers R. Amaranatha Reddy Ton Verhulst Carsten Tschierske Antonius T. M. Marcelis Ernst J. R. Sudh lter 《Liquid crystals》2006,33(6):681-688
Eight banana-shaped side chain liquid crystalline oligomers and polymers have been synthesized by hydrosilylation of vinyl-terminated bent-core mesogens with trimethylsilyl-terminated siloxanes. The synthesized oligomers and polymers, and their olefinic precursors, were investigated by polarizing optical microscopy (POM), differential scanning calorimetry, X-ray diffraction (XRD), electro-optical experiments and Maldi-Tof. The short-tailed olefins form a Colr mesophase, whereas those with longer chains exhibit the SmCPA mesophase. All the oligomers and polymers studied show liquid crystalline properties and do not crystallize upon cooling. Most oligomers with around four repeating siloxane units, show a lamellar (layer) structure and antiferroelectric switching properties, the SmCPA phase. XRD shows that the layer spacings are hardly influenced by the length of the terminal tails. The oligomer prepared from the smallest olefinic precursor, having the shortest alkyl tail, shows an XRD pattern reminiscent of a columnar phase, although POM displays domains of opposite chirality, and no switching behaviour could be detected. The polymers with around 35 repeating siloxane units are liquid crystalline, but due to their high viscosity a thorough characterization of the liquid crystalline phases was impossible. 相似文献
80.
Uwe Risse Elke Flammenkamp Antonius Kettrup 《Fresenius' Journal of Analytical Chemistry》1994,350(7-9):454-460
A novel denuder system for the determination of airborne hazardous organic substances is presented. A special wall coating technique allows to reuse the denuder after a regeneration procedure. The denuder system has been designed for workplace air monitoring and can be used in combination with filters and back-up adsorbents to distinguish between the gaseous and the particle-bound phase of a compound. The use of dynamically generated test gases has been enabled reliable determinations of uptake rates and adsorption capacities as well as desorption efficiencies at different conditions. The penetration of particulate matter through the denuder has been examined.Dedicated to Professor Dr. Dieter Klockow on the occasion of his 60th birthday 相似文献