L. A. Kutulya

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.

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.

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.

Twist grain boundary states in non-chiral smectogen-chiral dopant

The liquid crystalline systems studied consisted of non-chiral mesomorphic esters [the eutectic mixture of 4-n-hexyloxyphenyl 4-n-octyloxybenzoate and 4-n-octyloxyphenyl 4-n-hexyloxybenzoate] and structurally similar chiral dopants (N-arylidene derivatives of S-1-phenyl- and S- 1-benzyl-ethylamine). Twist grain boundary phases occur between the cholesteric and smectic C* or smectic A phases in all the investigated systems. The different structures of these TGB phases (TGBA and TGBC) are proved by small angle X-ray scattering and textural studies. The concentration and temperature ranges of the TGB phases are defined by the twisting power of the chiral dopants and their own mesomorphic peculiarities. The experimental dependences of TGB phase temperature range on cholesteric helical twist are influenced by a ratio change of the optically active and racemic forms of the dopant at a constant total concentration. The results obtained are discussed within Renns theory.

Relationship between the temperature dependence of the induced helical pitch and the anisometry of molecules of chiral dopants

The regularities of changes in the temperature dependence of the helical pitch P and the parameter dP/dt are analyzed for induced cholesteric liquid-crystal systems based on nematic 4-pentyl-4′-cyanobiphenyl, including chiral arylidene derivatives of (S)-1-phenylethylamine and (1R),(4R)-isomenthone. In the molecules of these compounds, the length of the π-electron arylidene fragment, the nature of the bridge group between its benzene rings and of the lateral substitution in the cyclohexanone ring, and the length of the terminal alkyl or oxyalkyl substituent are varied. The statistical molecular anisometry of the chiral dopants is calculated using the density functional method and the semiempirical AM1 method. It is shown that the temperature dependence of the induced helical pitch and, correspondingly, its quantitative characteristic dP/dt and the parameter dtt/dC, characterizing the effect of a chiral dopant on the thermal stability of the mesophase, are determined by the molecular anisometry of the chiral component.

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.

New chiral esters, diastereomeric 2-(4-carboxybenzylidene)-p-menthane-3-one derivatives, as components of LC systems with induced helical structure

Abstract Diastereomeric 1R, 4S- and 1R, 4R-2-carbomethoxybenzylidene-p-menthane-3-ones have been synthesized. The helical twisting power and the induced helical pitch temperature dependence have been measured for the liquid crystal mixtures based on the nematic 4-methoxybenzylidene-4′-butylaniline and 4-pentyl-4′-cyanobiphenyl containing the obtained diastereomeric chiral dopants. The distinction in the characteristics of the diastereomeric chiral dopants is discussed.

New (S)‐1‐phenylethylamine N‐arylidene derivatives as chiral dopants to liquid crystalline systems

New chiral N‐arylidene (S)‐1‐phenylethylamines with a 4,4″‐biphenylene group in the central path of the rigid core were synthesized and their mesomorphic properties investigated. The helical twisting power and the temperature dependences of the helical pitch and the selective light reflection were analysed for several liquid crystalline systems based on 4‐pentyl‐4′‐cyanobiphenyl, E63 (Merck) and 4‐(n‐hexyloxy)phenyl 4′‐(n‐butyl)benzoate containing new chiral components. The chiral compounds investigated induce helical ordering effectively in all the host materials and have significant potential for applications. The results obtained for the new chiral compounds are compared with those for some previously studied similar chiral additives.

New chiral imines based on S-α-phenylethylamine and S-α-benzylethylamine in induced cholesteric and smectic mesophases: II. Behavior of chiral dopants in ester liquid-crystal systems

The temperature dependences of the pitch of induced helical structures in the ester liquid-crystal systems containing hydroxyphenyl benzoate derivatives and chiral N-aroyloxybenzylidene-S-α-phenylethylamines or N-aroyloxybenzylidene-S-α-benzylethylamines have been measured. The twisting power of chiral dopants is calculated and the temperature dependence of the helical pitch in the induced cholesteric (N*) and smectic C* mesophases is quantitatively characterized. The parameters A = dTis/dC that characterize the effect of dopants on the thermal stability of the N* phases are determined from the concentration dependences of the cholesteric-isotropic transition temperature Tts for the n-hexyloxyphenyl-n-butylbenzoate-chiral dopant systems. The results obtained are compared with the data for the 4-n-pentyl-4′-cyanobiphenyl (5CB)-based cholesteric systems induced by the chiral dopants under consideration.