- Vinyl-terminated liquid-crystalline dendrimers based on dendritic polyols and their siloxane-based elastomers
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A new series of side-chain liquid-crystalline dendrimers (LCDs) by grafting vinyl-terminated phenyl benzoate-based promesogens to a novel polypropyleneimine-derived dendritic polyols are reported. Polarized optical microscopy and X-ray diffraction studies
- Lin, Yuteng,Sun, Jianzhong
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- New SmCG phases in a hydrogen-bonded bent-core liquid crystal featuring a branched siloxane terminal group
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In this study, we synthesized three analogous bent-core molecules, a hydrogen-bonded complex and a covalent-bonded compound with branched siloxane units (H-SiO and C-SiO, respectively) and a hydrogen-bonded complex with an alkyl unit (H-Alk), and investigated the effects of the hydrogen bonding and branched siloxane terminal units on their mesomorphic properties. The covalent-bonded compound C-SiO and the hydrogen-bonded complex H-Alk exhibited typical SmCP phases; in contrast, the hydrogen-bonded complex H-SiO exhibited a series of general tilt smectic (SmCG) phases with highly ordered layer structures (i.e., SmCG2PF-USmCG2P A-SmCG2PF-SmCGPF upon cooling). During the SmCG-type phase transition process, a 2D-modulated ribbon structure transferred into highly ordered layers via undulated layers, as the hydrogen-bonding strength increased with reduced temperatures. As the SmCG domains were aligned under dc electric fields, a gradual decrease in the leaning angle from ca. 60° to 50° (while the tilt angle kept at ca. 31°) could be determined by in situ wide-angle X-ray scattering (WAXS). Combined with Fourier transform infrared and Raman spectroscopic data, our results suggest that the change in the leaning angle was governed by the competition of the hydrogen bonds and microsegregation of siloxane units within the bilayer structure of the hydrogen-bonded complex H-SiO. In addition, the ferroelectric-(antiferroelectric)-ferroelectric transitions proven by the switching current responses in the SmCG-type phases of H-SiO reveal that the polar switching occurred through collective rotations around the long axis of H-SiO. Therefore, novel SmCG phases with a series of highly ordered 2D-structures were induced by the effects of the hydrogen bonding and branched terminal siloxane unit in the bent-core hydrogen-bonded LC complex H-SiO.
- Chen, Wei-Hong,Chuang, Wei-Tsung,Jeng, U-Ser,Sheu, Hwo-Shuenn,Lin, Hong-Cheu
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p. 15674 - 15685
(2011/11/28)
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- BENT-CORE LC DECORATED GOLD NANOCLUSTERS
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Novel thiol-terminated bent-core liquid crystals (LCs) are used to decorate gold nanoparticles. Thioacetate or xanthate/xanthogenate functional groups are used to effect the attachment of the LCs to the gold nanoparticles. Such bent-core decorated nanoparticles may be dissolved in bent-core liquid crystal host media to provide polarizable systems which respond quickly to applied electric fields and exhibit other interesting and useful optical and electro-optic behaviour.
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- Bent-core liquid crystal (LC) decorated gold nanoclusters: Synthesis, self-assembly, and effects in mixtures with bent-core LC hosts
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We present the first synthesis of a series of thiol-, thioacetate-, and xanthate-terminated bent-core derivatives, as well as the preparation of gold nanoclusters using the thiol-terminated bent-core compounds. The mesomorphic properties of the bent-core compounds have been investigated by polarizing optical microscopy (POM), differential scanning calorimetry (DSC), small angle X-ray scattering (SAXS), and electro-optic tests. From this series, the mono-xanthate derivatives form rectangular or hexagonal columnar phases, and the mono-thiol derivative with shorter alkyl chains forms a metastable, likely smectic, phase. All other bent-core compounds and intermediates exclusively form disordered or multi-layer lamellar crystalline solid modifications. High-resolution transmission electron microscopy (HR-TEM) images of the bent-core functionalized gold nanoclusters prepared from the thiol-terminated derivatives, taken after slow evaporation of the solvent, provide evidence for the formation of self-assembled nanocluster arrays. Upon dispersion of these gold nanoclusters in two structurally related bent-core LC hosts (one forming a SmCPA, and the second with a terminal double bond displaying a Colr phase), a shift in the surface plasmon resonance was observed indicating a LC host-dependent aggregation of the nanoparticles. Finally, we report initial results on the effects of different concentrations of these nanoclusters on the thermal properties as well as the applied voltage/current response of the parent SmCPA host.
- Marx, Vanessa M.,Girgis, Hidy,Heiney, Paul A.,Hegmann, Torsten
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supporting information; experimental part
p. 2983 - 2994
(2010/02/27)
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- Influence of the core structure on the development of polar order and superstructural chirality in liquid crystalline phases formed by silylated bent-core molecules: Naphthalene derivatives
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Bent-core molecules based on a bent 2,7-disubstituted naphthalene unit and heptamethyltrisiloxane units at one or both ends of the aliphatic side chains were synthesized and investigated by polarized light microscopy, differential scanning calorimetry, X-
- Reddy, R. Amaranatha,Baumeister,Keith,Tschierske
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- Substituent Effects on the Enantioselective Hydrocyanation of Aryl Aldehydes
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A detailed study of the dipeptide catalysed enantioselective hydrocyanation of a series of O-substituted 4-hydroxybenzaldehydes has shown that adverse steric effects can occur leading to low enantiomeric excess (e.e.) values when the substituent is long and flexible.Similar hydrocyanation of several derivatives of 3,4-dihydroxybenzaldehydes have been shown to give very variable values of e.e.Hydrocyanation of 3,5-dimethoxy and 3,4,5-trimethoxybenzaldehyde consistently gave low values of e.e.
- Kim, Hyun J.,Jackson, W. Roy
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p. 1541 - 1548
(2007/10/02)
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