- Chiral polymorphism in new imine based rod-like liquid crystals
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New imine based rod-like compounds, composed of three-benzene-ring molecular core linked with azomethine as well as ester groups and terminated with (S)-3,7-dimethyloctyloxy chiral unit at one side have been synthesized. The other terminal position has been varied by using n-octyloxy/decyloxy/dodecyloxy groups to reveal chain length effect on mesophase behavior. The liquid crystalline properties of the new compounds have been investigated by polarizing optical microscopy, differential scanning calorimetry and electro-optic studies. The novel chiral calamitics derived from Schiff base or salicylaldimine-core show a chiral polymorphism comprising of blue phase and chiral nematic as well as smectics such as chiral tilted smectic and unidentified smectic mesophase.
- ?a?lar, Fatma P?nar,Akda?-K?l??, Huriye,Eran, Belk?z Bilgin,Ocak, Hale
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- Imine based chiral liquid crystals: Effect of varying the terminal substituent and orientation of ester linking unit
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New liquid crystalline compounds composed of three-benzene-ring molecular core comprising both the imine and ester linkage units, (S)-3,7-dimethyloctyloxy chiral unit at one of terminals and n-dodecyl/dodecyloxy group as other side chain have been synthesized and characterized to study the effect of varying terminal chains, the orientation of polar ester linking group and the presence of molecular chirality on mesophase properties of imine based calamitic compounds. The liquid crystalline properties of the compounds were investigated by differential scanning calorimetry, optical polarizing microscopy and electro-optic methods. As a result of the strong effect of chirality of (S)-3,7-dimethyloctyloxy chain, all Schiff bases (imines) exhibit enantiotropic chiral smectic C (SmC*), chiral nematic (N*) as well as SmX phase just below the SmC* phase and blue phase (BP) appearing monotropically. The SmC* phase shows ferroelectric switching behaviour with PS values in the range 70–130 nC cm?2. The alteration of the n-alkyl tail with an alkoxy chain gives rise to a significant increase up to 30 °C in mesomorphic transitions. The change in the orientation of polar ester linking group has no effect on the type and sequence of observed LC phase. As compared with (S)-4-(3,7-dimethyloctyloxy)phenol based imine derivatives (7a, 7b), the chiral nematic (N*) mesophase temperature range of (S)-4-(3,7-dimethyloctyloxy)benzoate based compounds (8a, 8b) significantly broadened. Additionally, a decrease on the phase transition temperatures occurred with regardless of introducing n-dodecyl/dodecyloxy group as side chains.
- Karanl?k, Gürkan,Ocak, Hale,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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- Propeller-like hydrogen-bonded banana-melamine complexes inducing helical supramolecular organizations
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The results of the study presented here show a new example of the use of liquid crystals and the interactions involved in the mesomorphic state to build up complex molecular organizations. We have pursued a design strategy in which hydrogen bonding allows
- Barbera, Joaquin,Puig, Laura,Romero, Pilar,Serrano, Jose Luis,Sierra, Teresa
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p. 4487 - 4492
(2007/10/03)
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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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