Alois Villiger

Aryl couplings with heterogeneous palladium catalysts

Abstract The coupling reaction of diverse phenylboronic acids with aryl halogenides and -triflates has been performed by the use of simple palladium hydrogenation catalysts. Evidence for a heterogeneous type of catalysis has been obtained.

Polar Alkenyls: Physical Properties and Correlations with Molecular Structure of New Nematic Liquid Crystalsf

Abstract The elastic constants k11, k22, k33 , the bulk and rotational viscosities, the birefringence, the static dielectric and electro-optical properties in TN-LCDs of new, positive dielectric and electro-optical properties in TN-LCDs of new, positive dielectric nematic liquid crystals, namely polar alkenyls, are reported. The molecules comprise a double bond in their hydrocarbon side chain as well as different rigid cores, namely directly- and ethane linked PCH-cores as well as heterocyclic (dioxane) cores. Despite their dielectric and conformational similarity, large variations of the elastic constants depending on the position of the alkenyl double bond are shown to result in alkenyls with PCH cores. This leads to variations of k33/k22 and k = k11 + k 33-2k22)/4 among different alkenyls with the same chain length of almost a factor of 2 at constant reduced temperature (Tc-10°C). From molecular modelling follow rod-shaped van der Waals conformations with constant length/width ratio L/ W for all direct...

Synergisms, structure-material relations and display performance of novel fluorinated alkenyl liquid crystals

Abstract Several new classes of low polarity, low viscosity and optically weakly anisotropic two and three ring fluorinated liquid crystals with alkenyl side chains are presented. Synergisms which lead to a number of favourable material properties are shown to result from systematic changes of (a) para and lateral fluorination of the benzene ring in the rigid cores, (b) variations of double bond positions in the alkenyl side chains and (c) from replacing cyclohexane core rings by dioxane rings. A broad range of dielectric anisotropies −0.3 < Δ∊ < 13, broad nematic meso-phases, low rotational, λ and bulk viscosities, n, (22°C) < 10cP as well as visco elastic ratios as low as λ/k (22°C) = 3.8 × 10–12m-12s-1 follow; were K = K11 + (K33 - 2K22)/4. As a consequence a wide range of optical threshold voltages V10 and short response times result in field-effect liquid crystal displays. The low ratios κ/Δ∊ of the heterocyclic representatives among the new compounds lead in twisted nematic displays to threshold vol...

New Nematic Liquid Crystals: Influence of Rigid Cored, Alkenyl Side-Chains and Polarity on Material and Display Properties

Abstract From the design of non-polar molecular structures exhibiting different rigid cores and isolated C=C double bonds in different side-chain positions and from investigations into the static dielectric birefringence, viscous, and all three elastic constants k 1, k 2, k 3, new, negative dielectric anisotropic nenatic liqueid crystals result, namely apolar alkenyls, which are shown to cover a wide range of materail porpertie, including large twist constants k 2. The combination of double bonds in 4-position, with rigid cores comprising heterocyclic rings is shown to lead to exceptionally low elastic rations k 3/k 1 ∼ 0.4 with simultaeoulsy low optical anisotropies and low roatational viscosities γ1. Moreover, laterally substituted alkenyls are shown to exhibit large negative dielectric anisotropies rendering them applicable for low viscous, positive contrasat guest-host mixtures with high order parameters 0.72≤ S ≤ 0.78. The stability of the new nematics comprising isolated double bonds is shown to be ...

New Liquid Crystal Materials; Physical Properties and Performance in Displays for Automobile, High Information Density and Guest-host Applications

Abstract Four novel liquid crystal classes are presented, namely bi-, tri-, and tetracyclic ethanes, pyridazines, and tetracyclic chloro-diesters. Each class exhibits distinct physical characteristics, such as low viscosities η − 12 cP, low elastic ratios k33/k11 ∼ 1, large mesomorphic ranges −40°C. 250°C, large negative dielectric anisotropies δ e − 9 and/or low dielectric relaxation frequencies f e ∼ 1 kHz. It is shown that the dielectric Debye relaxation time τ characterizing the hindered rotation of polar nematic molecules around their short axes is much more affected by molecular structural factors than by their rotational viscosity γ1. The material and electro-optical properties of mixtures for twisted nematic and guest-host LCDs comprising the new compounds are presented. The mixtures cover a wide range of applications such as high contrast, fast and multiplexable automotive TN-LCDs; positive and negative contrast guest-host LCDs; high-information density matrix, and dual-frequency addressable LCDs.

Ferroelectric liquid crystals VI. Chiral 5-alkyl-2-phenylpyrimidines

Abstract Over 50 variously substituted 5-alkyl-2-phenylpyrimidines have been synthesized. The effect of the presence of an additional olefinic double bond in the terminal position of the alkoxy chain or of a trans-1,4-disubstituted cyclohexane ring on the liquid crystal transition temperatures of these systems has been studied in detail. All of the phenyl-pyrimidines studied possess an optically active centre at the point of methyl branching of one of the terminal carbon chains. The dependence of the transition temperatures of these systems on the position of the chiral centre has also been investigated. The effect of chain length has also been studied for various homologous series of mesogens. Almost all of the 5-alkyl-2-phenylpyrimides prepared exhibit enantiotropic chiral smectic C and cholesteric mesophases, some at and just above room temperature.

Smectic C phenylpyridines with an alkenyloxy chain

Abstract The known 5-n-alkoxy-2-[4-(n-alkoxy)phenyl]pyridines exhibit high smectic C transition temperatures as well as various highly ordered smectic mesophases. An unsaturated carbon-carbon double bond has now been introduced into the terminal alkoxy chain of these heterocyclic materials to produce the corresponding alkenyloxy substituted derivatives. The postion and nature (E/Z) of the double bond has been varied systematically and the effect on the liquid crystal transition temperatures determined. A number of homologous series of the most promising alkenyloxy substituted materials has been prepared and evaluated. The position and nature (E/Z) of the double bond changes the conformation of the alkenyloxy chain to a significant degree. This can lead to slightly higher smectic C transition temperatures for compounds with a trans-double bond (E) at an even number of carbon atoms from the molecular core. However, the highly ordered mesophase transition temperatures are increased to a greater degree leadin...

The influence of double bonds in the terminal chain of 2-ring compounds on the physical properties of S*c mixtures

Abstract We present the properties of S*c mixtures containing new 2-ring 5-n-alkyl-2-(4-n-alkenyloxyphenyl)pyridines and pyrimidines with systematically varying positions and configurations of the double bond Trans configurations at odd positions (counting the number of atoms from the core including the oxygen and the first carbon atom of the double bond) suppress the SA phase, increase the S*c tilt angle, Θ, and the spontaneous polarization, P s, and lead to long switching times τ. Cis configurations at even positions suppress the nematic phase in favour of smectic phases, decrease Θ and P s, and shorten τ. Other positional configurational combinations strongly reduce the clearing point. Furthermore, our results indicate that the preferred conformation of the alkenyloxy chain consists of alternating cis and trans units.

2-(4-Alkylphenyl)-5-(alkenyloxy)pyrimidines: Synthesis, liquid crystal transition temperatures and some physical properties

Abstract We have recently reported the introduction of a carbon-carbon double bond into a wide variety of 5-n-alkyl-2-(4-n-alkoxyphenyl)pyrimidines to produce the corresponding alkenyloxy derivatives. The position and nature (E/Z) of the double bond were varied systematically and the effect on the liquid crystal transition temperatures studied. The position and nature (E/Z) of the double bond changed the conformation of the alkenyloxy chain substantially. This resulted in higher smectic C and nematic transition temperatures for compounds with a trans-double bond (E) at an even number of carbon atoms from the molecular core. Significantly lower transition temperatures (including the melting point) were observed for materials with a cis-double bond (Z) at an odd number of carbon atoms from the molecular core. We have now performed the same operation on the related 2-(4-n-alkylphenyl)-5-n-alkoxypyrimidines to produce the corresponding alkenyloxy derivatives. An interesting feature of the new results is the h...

Novel ferroelectric smectic C liquid crystal mixtures for display applications

Abstract Novel long-pitch ferroelectric smectic C liquid crystal mixtures are reported which combine a broad chiral smectic C temperature range with a low birefringe. Due to their fast response times and excellent thermal and photochemical stability, these mixtures are particularly well suited for fast switching electro-optic displays based on the surface-stabilized geometry.