Richard Buchecker

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.

Invited Lecture. Material properties, structural relations with molecular ensembles and electro-optical performance of new bicyclohexane liquid crystals in field-effect liquid crystal displays

Abstract Several new classes of polar and non-polar bicyclohexane liquid crystals comprising alkenyl side chains are presented. The compounds exhibit low optical anisotropies, Δn, 12 × 10−12 N, to low viscoelastic ratios γ1/k and to short response times in field-effect liquid crystal displays (LCDs). Strong odd-even effects occur in the bend/splay elastic ratio k 3/k 1 upon shifting the alkenyl double bond from even into odd side chain positions. As a result the ratio k 3/k 1 can be tuned over the wide range 0·9 ≲ k 3/k 1 ≲ 3·0. Correlations between the electro-optical properties of twisted nematic, supertwisted nematic, optical mode interference LCDs and material parameters demonstrate the high degree of multiplexability of the new compounds. Roche interactive molecular modelling is applied to determine the possible equilibrium configuration not only of singl...

Strongly non-linear optical ferroelectric liquid crystals for frequency doubling

Abstract From our research for novel non-linear optical (NLO) materials for frequency doublers and optical modulators we report on new ferroelectric liquid crystals, which for the first time, exhibit second order NLO coefficients (for example d 22 = 5 pm V−1, which are comparable to those of state of the art inorganic NLO materials. The novel compounds contain 5-amino-2-nitrophenyl groups attached close to the chiral centres. The switching behaviour of the new compounds, their spontaneous polarization, as well as their frequency doubling of Nd:YAG laser pulses in the S*c and in the glass state, are reported. Moreover their waveguiding properties are presented.

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...

Synthesis, Physical Properties and Structural Relationships of New, End-Chain Substituted Nematic Liquid Crystals

Abstract New nematic liquid crystalline phenylcyclohexanes with (i) a terminal side-chain vinylic group some distance from the rigid core and (ii) both polar and non-polar terminal side-chain groups, were synthesized. Investigations of their elastic, birefringence, dielectric and rotational viscous properties have shown several new odd-even effects. These are attributed to side-chain Simultaneous odd-even effects were found for δϵ, δn, k 33/k11 and K = k 11 + (k 33 - 2k 22)/4. Furthermore, unusually low twist elastic constants, k 22 were obtained for polar 6-alkenyls as well as for compounds exhibiting groups with permanent dipole moments in even side-chain positions.

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 ...

Structure of optically active compounds and ferroelectric properties of liquid crystals

Abstract A new series of optically active dipole dopants - diesters of 4,4″-terphenyl dicarboxylic acid - have been prepared. Most of the components are high melting substances. Some of 2-chlorine substituted compounds show a chiral smectic C* phase. The Ps value induced by optically active dipole dopants depends on several factors such as the magnitude of the dipole moment and the length of the alkyl tail at the C*-atom, the degree to which rotations of the molecule and the chiral center are hindered. In some cases the experimental PS value of the FLC-mixture induced by a pair of dopants with same Ps sign and opposite helix handedness is higher than the sum of the PS values induced by each dopant independently.

Some new α-fluoro esters incorporating a cyclohexane ring as chiral dopants for ferroelectric mixtures

Abstract A wide variety of new, optically active α-fluoro esters incorporating a trans-1,4-disubstituted cyclohexane ring and several different core structures have been prepared. Several of these new materials exhibit an enantiotropic chiral smectic C mesophase at elevated temperatures, characterized by high spontaneous polarization, long pitch and low rotational viscosity. Furthermore, they possess exceptional thermal, chemical and photochemical stability. Thus these novel α-fluoro esters incorporating a cyclohexane ring are excellent chiral dopants for chiral smectic C mixtures for utilization in the surface stabilized ferroelectric liquid crystal display.

Polar nematic methyl (E)-[trans-4-cyclohexyl-substituted]allyl ethers: Synthesis, liquid crystal transition temperatures and some physical properties

Abstract We have introduced an oxygen atom and a carbon-carbon double bond with a trans-configuration (E) into the terminal alkyl chain attached to the cyclohexyl ring of a variety of two- and three-ring nematic liquid crystals of positive dielectric anisotropy. The new polar two-ring methyl (E)-allyl ethers often possess low melting points, but are not mesomorphic in general. The related three-ring methyl (E)-allyl ethers exhibit high clearing points and wide nematic ranges. Comparisons with the corresponding derivatives incorporating either just an oxygen atom or just a carbon-carbon double bond in the same position indicate that synergetic effects lead to broader nematic phases than would otherwise have been expected. This is partially due to the low smectic transition temperatures observed for the methyl (E)-allyl ethers. Selected physical properties of three binary mixtures of a weakly polar standard nematic liquid crystal and three difluoro-substituted (polar) liquid crystals (including the new ethe...

New Liquid Crystals: The Mesomorphic Properties of Mono-and Bisalkenyl(oxy)substituted Esters

Abstract 61 mono- and 16 bisalkenyl(oxy)substituted bi- and tricyclic esters have been synthesized by systematically varying both the position of the isolated C, C-double bonds and the nature of the central core ring system. The influences of the various structural parameters on the mesomorphic properties are discussed and the observed nematic and/or smectic thermal stabilities are compared with those of the corresponding saturated alkyl(oxy) analogs.