- Mixed-dimer formation in binary systems of 4-substituted benzoic acids and structure considerations
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The phase behavior of binary systems of 4-substituted benzoic acids is governed by the formation of mixed, dimers. This study was conducted to determine the effect of the components' structural difference on mixed-dimer formation in crystalline and liquid-crystalline phases. The phase diagrams of two systems, with 4-[(S)-(-)-2-methylbutoxy]benzoic acid (MBOBA) as one component and 4-(hex-5-enoxy)benzoic acid (HOBA) and 4-(dec-9-enoxy)benzoic acid (DOBA), respectively, as the second component, were determined by differential scanning calorimetry, polarized-light microscopy, and X-ray diffraction. The MBOBA-HOBA system exhibited a cholesteric phase, two solid solutions, and above 58°C for compositions between 40 and 80 mol% HOBA a crystalline phase of mixed dimers. The MBOBA-DOBA system showed a crystalline phase of mixed dimers at all compositions, a cholesteric phase, and a twisted smectic C phase, which was dominated by mixed dimers at 60 and 70 mol.% DOBA. We conclude that liquid-crystalline phases are generally dominated by mixed dimers, but in crystalline phases the formation of mixed dimers is promoted by a greater difference in molecular structure. The crystal structure of two of the pure compounds MBOBA and DOBA and comparable compounds have been determined for an evaluation of the arrangements of the molecules in the crystal and liquid-crystalline state.
- Roman, Maren,Kaeding-Koppers, Annett,Zugenmaier, Peter
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- Synthesis and mesomorphic properties of new organosiloxane chiral calamitic liquid crystals
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A new chiral calamitic compound consisting of a phenyl core that is connected through ester linkers to a benzoate carrying a chiral (S)-2-methylbutoxy group at one side and a biphenyl carboxylate with an undecenyloxy chain at other side has been synthesized. Additionally, the siloxane substituted derivatives and a dimer with these two identical chiral calamitics linked by a disiloxane spacer have been obtained via hydrosilylation reaction to study the effect of combining the chiral moiety and siloxane segments within the same structure on liquid crystalline properties. The chiral calamitic compound and derivatives with a siloxane end-group or a siloxane spacer have been characterized using classical spectroscopic methods (1H NMR, 13C NMR, 29Si NMR and MS) and elemental analysis (EA). The liquid crystalline properties of all new compounds were investigated by differential scanning calorimetry, optical polarizing microscopy, X-ray scattering and electro-optic methods. With the introduction of a siloxane end-group to the vinyl-terminated calamitic compound exhibiting enantiotropic chiral nematic phase (N*) and chiral tilted smectic phase (SmC*), the occurrence of stable smectic phase was strongly promoted. In a similar way, the dimer with two identical calamitic mesogens connected by a disiloxane spacer exhibited a wider smectic mesophase interval in addition to the presence of N* mesophase. The new mesogens exhibit a ferroelectric switching with PS of around 200 nC cm?2 in their chiral tilted smectic (SmC*) mesophase range. The transition temperatures of organosiloxanes are considerably lower than that of olefinic precursor.
- Ocak, Hale,Karaa?a?, Burcu,Akda?-K?l??, Huriye,Jeannin, Olivier,Camerel, Franck,Bilgin Eran, Belk?z
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- Extraordinary magnetic field effects on the LC phases of homochiral and racemic 4-cyanoresorcinol-based diamagnetic bent-core mesogens
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4-Cyanoresorcinol based bent-core compounds combining one branched chiral with one achiral linear end-chain have been synthesized in enatiomerically pure and one compound also in racemic form. All homochiral compounds form a chiral cybotactic nematic phase at relatively low temperature with a selective reflection ranging from the near IR to near UV. For the compound with the longest chains superparaelectric and antiferroelectric switching smectic phases were observed, whereas the corresponding racemate is non-polar. This is attributed to sterically induced polarization by the denser packing of uniform enantiomers due to chirality synchronization of the helical conformers. For the racemic mixture this chirality synchronization requires additional surface stabilization. There are unprecedented effects of an applied magnetic field (1 T) on the LC phases, leading to a layer shrinkage by 6-13% for the enantiomer and a layer expansion by 5-8% for the racemate. It is proposed that the magnetic field couples with the π-systems of the almost rod-like molecules. For the racemate this increases the core order, whereas for the enantiomer the reduction of the heliconical twist is considered to provide the major effect. These magnetic field effects could lead to new applications of chiral LC materials at the cross-over between rod-like and bent shapes.
- Ocak, Hale,Bilgin Eran, Belk?z,Nuray, Sevgi,?zkonstanyan, Aykun,Poppe, Silvio,Tschierske, Carsten
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p. 1895 - 1910
(2021/03/01)
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- Optically active 4-(4-{4-[(2S)-(2-methylbutoxy)]benzoyloxy}-phenyldiazenyl)benzaldehyde
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4-(4-{4-[(2S)-(2-methylbutoxy)]benzoyloxy}phenyldiazenyl)benzaldehyde was synthesized and its structure was identified.
- Kuvshinova,Burmistrov,Novikov,Aleksandriiskii,Koifman
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p. 195 - 197
(2015/04/14)
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- Twist grain boundary (TGB) states of chiral liquid crystalline bent-core mesogens
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4-Cyanoresorcinol derived bent-core molecules with a chiral (S)-2-methylbutoxy chain form liquid crystalline phases with TGBA- and TGBC-like structures at the transition from cybotactic nematic via SmA to SmC phases. This journal is
- Ocak, Hale,Bilgin-Eran, Belkiz,Güzeller, Dilek,Prehm, Marko,Tschierske, Carsten
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supporting information
p. 7512 - 7515
(2015/05/04)
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- Multifunctional supramolecular dendrimers with an s-triazine ring as the central core: Liquid crystalline, fluorescence and photoconductive properties
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Novel liquid crystal (LC) dendrimers have been synthesised by hydrogen bonding between an s-triazine as the central core and three peripheral dendrons derived from bis(hydroxymethyl)propionic acid. Symmetric acid dendrons bearing achiral promesogenic units have been synthesised to obtain 3:1 complexes with triazine that exhibit LC properties. Asymmetric dendrons that combine the achiral promesogenic unit and an active moiety derived from coumarin or pyrene structures have been synthesised in order to obtain dendrimers with photophysical and electrochemical properties. The formation of the complexes was confirmed by IR and NMR spectroscopy data. The liquid crystalline properties were investigated by differential scanning calorimetry, polarising optical microscopy and X-ray diffractometry. All complexes displayed mesogenic properties, which were smectic in the case of symmetric dendrons and their complexes and nematic in the case of asymmetric dendrons and their dendrimers. A supramolecular model for the lamellar mesophase, based mainly on X-ray diffraction studies, is proposed. The electrochemical behaviour of dendritic complexes was investigated by cyclic voltammetry. The UV/Vis absorption and emission properties of the compounds and the photoconductive properties of the dendrons and dendrimers were also investigated.
- Bucos, Madalina,Sierra, Teresa,Golemme, Attilio,Termine, Roberto,Barbera, Joaquin,Gimenez, Raquel,Serrano, Jose Luis,Romero, Pilar,Marcos, Mercedes
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p. 10027 - 10037
(2014/08/18)
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- Bent-core compounds with two branched chains: Evidence of a new dark conglomerate mesophase
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Biphenyl-3,4′-diol derived bent-core compounds with branched side chains have been synthesized and characterized to study the influence of terminal branched groups on mesophase properties and transition temperatures of bent-core mesogens. The liquid crystalline properties of the compounds were investigated by differential scanning calorimetry, optical polarizing microscopy and X-ray scattering. Depending on the length of the chain, the size of molecular branches and the position of branched chains, either enantiotropic or monotropic rectangular columnar phases were observed. For one of the compounds combining two different branched side chains, a new type of optically isotropic dark conglomerate phase (MIso[*]) was found. It is proposed to be a distorted version of a non-tilted or only slightly tilted B6-like intercalated smectic phase with additional in plane order.
- Ocak, Hale,Bilgin-Eran, Belkiz,Prehm, Marko,Tschierske, Carsten
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p. 4590 - 4597
(2013/07/26)
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- Chirooptical and photooptical properties of a novel side-chain azobenzene-containing LC polymer
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A novel chiral-photochromic side-chain polyacrylate with azobenzene fragments in the side groups has been synthesised. It was shown that the polymer forms a smectic phase and a cholesteric supramolecular helical structure with selective light reflection in IR spectral range. Thin spin-coated films of the polymer were prepared and their photooptical and chirooptical properties were studied in detail. It was found that UV irradiation of the films led to E-Z isomerization of the azobenzene moieties with high conversion, which is dependent on thermal prehistory of the films. Subsequent action of visible light results in partial recovery of the E-isomer content, whereas annealing leads to the full back conversion. Circular dichroism (CD) measurements revealed formation of the helical supramolecular structure even in the initial spin-coated polymer films. The E-Z isomerization induces complete disruption of helical order in non-annealed films of the polymer, whereas in the smectic phase of the annealed film only a significant decrease in CD values was found. In addition, the photoorientation phenomena induced by polarized light were studied. It was shown that polarized light induces linear dichroism in the films provided by azobenzene group orientation and the dichroism is stable at room temperature for a prolonged time. These combined chirooptical and photooptical features of this novel polymer enable one to consider this multifunctional compound as a promising material for photonics and for optical applications.
- Bobrovsky, Alexey,Shibaev, Valery,Hamplova, Vera,Kaspar, Miroslav,Glogarova, Milada
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experimental part
p. 789 - 799
(2011/06/20)
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- Liquid crystal compounds, mixtures and devices
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An electroclinic device having two spaced cell walls each bearing electrode structures and treated on at least one facing surface with an alignment layer, a layer of a smectic liquid crystal material enclosed between the cell walls, where the liquid crystal material contains one or more of the compounds described by formula I as defined in the specification.
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Page column 8
(2008/06/13)
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- Liquid crystal compounds, mixtures and devices
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An electoclinic device having two spaced cell walls each bearing electrode structures and treated on at least one facing surface with an alignment layer, a layer of a smectic liquid crystal material enclosed between the cell walls, where the liquid crystal material contains one or more of the compounds described by formula I as defined in the specification.
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- Synthesis and structure of poly(phenyl isocyanate)s bearing an optically active alkoxyl group
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Novel optically active phenyl isocyanate derivatives (1-6) bearing an (R)-sec-butoxy, (S)-2-methylbutoxy or (S)-3,7-dimethyloctyloxy group at the meta or para position on the phenyl ring were prepared and polymerized with an anionic initiator in tetrahydrofuran (THF). The resulting polymers from 1, 2, 4 and 6 showed much greater specific rotation than that of the corresponding monomers and an intense circular dichroism (CD) band in the main-chain absorption region, indicating that these polymers have a predominantly one-handed helical conformation in solution. On the other hand, the polymers obtained from 3 and 5 showed a much smaller specific rotation than that of the above polymers at room temperature. The polymers from 2 and 5 showed a remarkable change in optical activity with change in temperature, and the specific rotation of the polymers changed from a positive to a negative value with decrease in temperature. The CD band of the polymers in the absorption region due to the main chain changed from a positive to a negative peak with a change in specific rotation. These results indicate that poly-2 and poly-5 undergo a thermally induced helix-helix transition in THF. The temperature for the helix-helix transition of poly-2 was independent of the degree of polymerization. Poly-2 exhibited a reversible helix-helix transition in chloroform and diethyl ether and also in THF, whereas in toluene and dichloromethane such a transition was not observed. Copyright
- Hino, Kyoko,Maeda, Katsuhiro,Okamoto, Yoshio
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p. 361 - 367
(2007/10/03)
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- A Comprehensive Approach to (S)-(-)-2-Methyl-1-Butanol as a Convenient Precursor for Synthesis of Chiral Liquid Crystals
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The chemistry of S-(-)-2-methyl-1-butanol leading to chiral liquid crystals (CLC) and their intermediates is summarized and new facile synthetic methods are described.Efficiency of the presented methods is discussed and illustrated with syntheses of several known and new CLC as well as the corresponding chiral intermediates.The newly synthesized chiral compounds display cholestic and smectic phases.Keywords: (S)-(-)-2-methyl-1-butanol, (S)-(+)-methyl-1-butyl benzenesulfonate, chiral liquid crystals, smectic C
- Kaszynski, P.,Jawdosiuk, M.
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- The Preparation and Thermal Properties of Terminal Disubstituted N-(4-Benzoyloxybenzylidene)anilines
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The homologous series of N--4-(2-methylbutoxy)aniline (1), and N-benzylidene>-4-n-alkoxyaniline (2), and N--4-(2-methylbutoxy)aniline (3) where the 2-methylbutoxyl group has an S-configuration, have been prepared.Series 1 and 2 form a chiral smectic C (S*C) phase in addition to a cholesteric (Ch) and a chiral smectic G (S*G) phases, and series 3 form (S*C) and Ch phases.
- Takenaka, Shunsuke,Ikemoto, Tetsuya,Kusabayashi, Shigekazu
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p. 3965 - 3966
(2007/10/02)
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