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Organic Materials for Third-Order Nonlinear Optics
Published in Hari Singh Nalwa, Seizo Miyata, Nonlinear Optics of Organic Molecules and Polymers, 2020
perpendicular geometries of the nematic liquid crystal 5CB. A strong nonlinear birefringence in the nematic phase is visible for parallel and perpendicular polarizations differing in magnitude as well as sign. These results were consistent with laser heating of the sample and the consequent reduction of orientational order. At the 10-ms timescale, n2 values of 5CB measured for the parallel and perpendicular polarizations were "1.30 X IO ; esu and +0.26 X 10 " esu, respectively, at 514 nm.453 Table 63 lists the n2 values of a variety of liquid crystals at different wavelengths.454 The d22 doped (0.2%) 8CB exhibited n2 values of "26 X IO"11 and +3.7 X 10 1 esu for parallel and perpendicular directions, respectively, at 22 "C using a7-ns pulsewidth. The chemical structures of 4-(l-octynyl)-4'-cyanobiphcnyl (OPL-7-1) (Structure 3), 4,4'-dipentylazoxybenzenc (OPL-10-1) (Structure 4), 4,4'-dihexylazoxyben- zenc (OPL-10-2) (Structure 5), 4-cyano-4'7i-alkyl-/?-terphenyl (T15) (Structure 6), CB15 (Structure 7), cyclohexylcyclohexane (ZL1-1538) (Structure 8), and phenylpyrimidine (ZL1-2302) (Structure 9) are
Emissive Nanomaterials and Liquid Crystals
Published in Klaus D. Sattler, 21st Century Nanoscience – A Handbook, 2020
Marianne E. Prévôt, Julie P. Vanegas, Elda Hegmann, Torsten Hegmann, Julia Pérez-Prieto, Yann Molard
Clustomesogens show several major characteristics: a deep red luminescence with quantum yields ranging from 0.1 to 0.7 depending on the nature of the ligands associated with the inorganic cluster, a self-organization at the nanometer scale as a result of molecular ordering events that produce supramolecular rods or discs, the presence of organic units ensuring their solubility in organic solvents, and birefringence. They are not only useful as bulk material but also dispersed as emissive dopant (or additives) in commercial liquid crystals. For example, the presence of cyanobiphenyl units within the organic matrix in some of the clustomesogens (see Table 6.2) provides a structural analogy to certain commercial liquid crystal singles such as those of Merck marketed under the name of nCB or nOCB, where n is the number of carbon atoms in the aliphatic chain (see, for example, 5CB in Figure 6.2), or mixtures such as E44 or E7.
Wetting Phenomena Inside Carbon Nanotubes
Published in Victor M. Starov, Nanoscience, 2010
Large carbon nanopipes have been filled with several polar and nonpolar liquids under the optical microscope.20 Similarly, carbon nanopipes have been filled, by capillary force alone, with a liquid crystal (5CB).49 The filled nanotubes where then imaged in the ESEM, using a cooling stage to offset the heating generated by the electron beam (Figure 29.8). A good wetting of the carbon surface by the liquid crystal is observed, with low contact angles and the formation of liquid crystal films on the surface. Almost complete spreading (contact angle <5°) of the liquid crystal was observed on carbon nanofilms having the same chemistry and structure of the carbon nanopipes.
Enhancement of electro-optical properties and phase transition temperature of thermotropic liquid crystal 5CB by doping with 4-n-pentylbenzoic acid
Published in Liquid Crystals, 2023
The commercial liquid crystalline materials nematic 4-cyano-4'-pentylbiphenyl (5CB) from SYNTHON Chemicals GmbH & Co. KG, Germany, with phase sequence (Crystal 18 ºC Nematic 35.4 ºC Isotropic) were used as the host material. In addition, the guest material 4-n-pentylbenzoic acid (PA) (purchased from the same provider) was used as the dopant material (guest). Both materials, their chemical names and structural formulas are given in Table 1, were used as received without further purification. 5CB is a single molecular component material with a positive dielectric anisotropy of = 11.5 at room temperature [31]. At the same time, PA has a narrow nematic phase above 100°C and weak dielectric anisotropic (about = 0.5) [32,33].
Probing the orientation of porphyrin oligomers in a liquid crystal solvent – a triplet state electron paramagnetic resonance study
Published in Molecular Physics, 2019
Sabine Richert, Harry L. Anderson, Martin D. Peeks, Christiane R. Timmel
5CB molecules, as shown in Figure 1, have a rigid rod-like polarisable core and a flexible aliphatic end group. They belong to the class of thermotropic nematic liquid crystals, characterised by a long-range orientational order. Even if the two ‘ends’ of the liquid crystal molecules are not chemically equivalent, it has been found that nematic liquid crystals behave optically as a uniaxial material with a centre of symmetry [31]. To characterise the alignment of the liquid crystal phase, a vector, called the liquid crystal director , is typically defined, which represents the symmetry axis of the phase. Bulk order can be imposed onto the molecules forming the nematic liquid crystal phase by applying electric or magnetic fields or making use of coated surfaces [32]. The LC director, , then indicates the average alignment of all LC molecules. 5CB has phase transitions from the crystalline phase to the nematic phase and from the nematic to the isotropic phase at about 22.5C and 35C, respectively [33].
Enhanced stability of the nematic phase of 4-pentyl-4ʹ-cyanobiphenyl due to the dispersion of copper nanoparticles
Published in Liquid Crystals, 2023
Geetanjali Srivastava, Mayank Jaiswal, Praveen Kumar Singh, Amir Iqbal, Roman Dabrowski, Ravindra Dhar
Although a large number of LC-Nano composites have been studied in recent years for various reasons as discussed above, but in most of the work, NPs decrease isotropic-nematic transition temperature along with an undesired increase in the ionic conductivity [21,28]. However, in some reports, isotropic-nematic transition temperature has increased [29,30] along with improvement in other physical properties due to the presence of ferroelectric [7,9,11,28,31] or functionalised NPs of small size [12,14,32–35]. In the continuation of these studied, in the present work, we are report the effect of copper NPs (CuNPs) on the thermodynamic stability as well as the optical and electrical properties of meso phases of 4-pentyl-4′-cyanobiphenyl (5CB). 5CB is a well-known liquid crystalline material and is suitable as a base material for various investigations because it has relatively wide temperature range nematic meso phase around room temperature alongwith high dipole moment almost along the long molecular axis leading to high-positive dielectric anisotropy. The molecular weight of 5CB is 249.35 g/mol [36]. Gray et al. synthesised 5CB for the first time at the University of Hull in 1973 [37]. Most of its properties are well-reported [12,38–40]. CuNPs are used in this study due to their strong catalytic activity which increases the reaction yield [41]. High boiling point of copper also enables CuNPs to be used in a variety of high-temperature and high-pressure chemical processes [42]. CuNPs have unique optical, electrical, and chemical properties that are influenced by their size, shape, content, crystallinity structure, and dielectric environment [43]. Additionally, the tremendous natural availability and inexpensive cost of copper make CuNPs particularly appealing.