1,720,981 research outputs found
Polymerizable Ester-Type Banana Liquid Crystals: A Comparative Study of Mesophase Behavior
No full textMicrowave-assisted deuterium exchange reaction for the preparation of reactive intermediates
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Conformations of Banana-Shaped Molecules Studied by 2H NMR Spectroscopy in Liquid Crystalline Solvents
No full textClPbis11BB and Pbis11BB, two banana-shaped mesogens differing by a chlorine substituent on the central phenyl ring, show a nematic and a B2 phase, respectively. To obtain information on the structural features responsible for their different mesomorphic behavior, a study of the preferred conformations of these mesogens has been performed by NMR spectroscopy in two nematic media (Phase IV and ZLI1167), which should mimic the environment of the molecules in their own mesophases, avoiding problems of sample alignment by a magnetic field. To this aim, 2H NMR experiments have been performed on selectively deuterated isotopomers of ClPbis11BB and Pbis11BB and of two parent molecules, ClPbisB and PbisB, assumed as models in previous theoretical and experimental conformational studies. We found that only a limited number of conformations is compatible with experimental data, often very different from those inferred from theoretical calculations in vacuo, indicating a strong influence of the liquid crystalline environment on molecular conformation. No significant differences between chlorinated and non-chlorinated molecules were found, this suggesting that chlorine does not change the molecular conformational equilibrium, as previously proposed
Deuterium and Carbon-13 NMR Study of a Banana Mesogen: Molecular Structure and Order
No full textThe orientational order and the molecular structure of the banana mesogen 4-chloro-1,3-phenylene bis{4,4'-(11-undecenyloxy)benzoyloxy}benzoate have been studied in its nematic phase by means of H-2 and C-13 NMR. A detailed discussion of orientational order parameters for either the entire molecular core or the selectively deuterated fragments, and geometrical features concerning the rigid core of the molecule is given. In particular, the angles thetai between the para axis of the aromatic ring and the long molecular axis for each lateral wing are estimated. Quantum chemical calculations on the rigid core made by the central five aromatic rings, employing the B3LYP density functional method, support the molecular structure derived from the NMR results. This study shows how important is the comparison between H-2 and C-13 NMR to better understand the real structure of banana-shaped compounds in their mesophases and further sheds light on the open question about chirality or achirality of banana molecules
Partially deuterated liquid crystal polymers: structure and orientational order by X-ray diffraction and 2H NMR
No full textDeuterium NMR evidences of slow dynamics in the nematic phase of a banana-shaped liquid crystal
No full textExperimental evidences of the slow dynamic behaviour of a banana-shaped liquid crystal (LC) detected by means of Deuterium Nuclear Magnetic Resonance (DNMR) in its nematic phase are reported. Deuterium line-shape and line-width trends of DNMR spectra of three selectively deuterium-labelled isotopomers of 4-chloro 1,3-phenylene bis {4-4 '-(11-undecenyloxy) benzoyloxy} benzoate (ClPbis11BB) are discussed in comparison with those of a deuterated probe dissolved in ClPbis11BB, used as LC solvent. Different dynamic regimes are observed for the central and lateral aromatic rings of the probe. These experimental remarks are discussed in terms of overall and internal molecular motions
Synthesis and mesophase structure of chiral liquid crystalline polysiloxanes containing a new phenyl benzoate mesogen
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