V. V. Vashchenko

Photosensitive chiral dopants with high twisting power

Abstract Quantitative investigations of E,Z-photoisomerization of chiral dopants (−)-2-arylidene-p-menthanones were carried out using solvents of different nature and various liquid crystalline matrices.

Dispersion of magnetic nanoparticles in a polymorphic liquid crystal

In order to enhance the phase stability of dispersions of magnetic nanoparticles (NPs) in a polymorphic liquid crystal, new ligands have been designed consisting of a terphenyl-based liquid crystalline core. The most stable dispersions were obtained with 7 nm super-paramagnetic Fe3O4 NPs decorated with the new ligands in place of 10 nm ferromagnetic CoFe2O4 spherical NPs.

Effect of Chiral Dopants Molecular Structure on Temperature Dependencies of Induced Cholesteric Helical Pitch

Abstract Effect of the chiral dopants molecular structure on the kind of the temperature dependencies of the induced cholesteric helical pitch has been studied for LC systems on the base of 4-pentyl-4′-cyanobiphenyl or 4-methoxybenzylidene-4-butylaniline including chiral S,α-phe-nylethylamine and E-1R,4R-2-(4-phenylbenzylidene)-p-menthane-3-one derivatives. The established correlations and their possible reasons have been discussed.

Enhanced orientational Kerr effect in vertically aligned deformed helix ferroelectric liquid crystals

We disclose the vertically aligned deformed helix ferroelectric liquid crystal whose Kerr constant (Kkerr≈130  nm/V2 at λ=543  nm) is around one order of magnitude higher than any other value previously reported for liquid crystalline structures. Under certain conditions, the phase modulation with ellipticity less than 0.05 over the range of continuous and hysteresis-free electric adjustment of the phase shift from zero to 2π has been obtained at subkilohertz frequency.

New Chiral 2-Arylidene-p-Menthane-3-Ones

Abstract Methylation of 1R,4R-2-arylidene-p-menthane-3-ones by methyl iodide stereo specifically yields 4-methyl derivatives with 1R,4R-configuration. An alternative way, (-)-menthone methylation and further crotonic condensation with aromatic aldehydes, leads to 1:1 mixture of 1R,4R- and 1R,4S-diastereomers. The properties of new 2-arylidene-4-methyl-p-menthane-3-ones as chiral components of the induced LC systems based on MBBA or 5CB have been compared with those for their 4-unsubstituted analogues and the corresponding 4-bromo derivatives.

Chiral organic compounds in liquid crystal systems with induced helical structure

Abstract In this work, some of the most important characteristics of chiral compounds as components of the liquid crystal (LC) systems are discussed. These characteristics are the helical twisting power of chiral dopants (CDs) in the induced cholesteric (N*) mesophases, the temperature dependence of the induced helical pitch (P) quantified by the dP/dT parameter and the influence of the CDs on the N* mesophase thermal stability characterized by the dTiso /dC parameter. The molecular structure influence on them for several systematic series of the N-arylidene derivatives of (S)-1-phenyl- and (S)-1-benzylethylamines as well as the chiral diastereomeric 2-arylidene-p-menthane-3-ones is considered.

New N-Arylidene (S)-1-Phenylethylamines as the Components of Induced Short-Pitch Cholesterics

Abstract New N-arylidene (S)-1-phenylethylamines with ester group in arylidene fragment have been synthesized. The chiral dopants helical twisting power and temperature dependence of the induced cholesteric helical pitch in LC systems based on 4-pentyl-4′-cyanobiphenyl have been studied as well as selective light reflection spectra and their temperature dependences for systems including nematic E63 (Merck) and new chiral components. An influence of the chiral dopant molecular structure on the mentioned characteristics of LC systems investigated was revealed. The induced cholesteric compositions with temperature-independent selective light reflection in visible range have been obtained.

Light Scattering of Short Helix Pitch Ferroelectric Liquid Crystal

Two new light scattering modes have been discovered in short helix pitch (p0 ≅ 350 nm) ferroelectric liquid crystal (FLC). One of the modes arises because of a special kind of the FLC structure non-uniformity that originates inherently as a new phenomenon if the helix pitch is very small. Another mode relates to the helix twisting after the driving voltage switching off.

Conformations of Z- and E-isomers of some chiral (1R,4R)-2-arylidene-p-menthan-3-ones

The 1Í NMR method in combination with molecular simulation was used to study conformations of Z- and E-isomers of (1R,4R)-cis-2-(4-methoxyphenyl)benzylidene-p-menthan-3-one. In solutions the Z-isomer, unlike the conformationally uniform Å-isomer, is an equilibrium mixture of chair conformers with the substantial predomination of one form with the axially oriented methyl and equatorial isopropyl groups (75—78%). The enone group is more nonplanar in the Z-isomer than in the Å-isomer. For the isopropyl fragment, the equiprobable existence of trans- and two gauche-rotamers for the Z-isomer and a substantial predomination of gauche-forms in the case of the E-isomer were established.

New chiral mesogens 3( R )-methylcyclohexanone derivatives

New chiral compounds 3R-methylcyclohexanone derivatives were synthesized. These compounds were revealed to exhibit the mesomorphic behavior within rather wide temperature ranges. Types of formed mesophases and phase transition temperatures were determined by polarizing microscopy, differential scanning calorimetry and small angle scattering of X-ray. Mesomorphic properties of the new chiral compounds were compared with those for the chiral 2-arylidene derivatives of 3R,6R-3-methyl-6-isopropylcyclohexanone (d-isomenthone) studied earlier. Distinctions between these two types of compounds in an ability to form mesophases and also in twisting properties as chiral dopants in induced cholesteric mesophases are considered.