Dipole Moments of 4-n Alkyl-4′-Cyanobiphenyl Molecules (from OCB to 12CB) Measurement in Four Solvents and Theoretical Calculations

Gueu, K. P.; Megnassan, E.; Proutière, A.

doi:10.1080/00268948608079550

Cited by 40 publications

(10 citation statements)

References 15 publications

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“…Table 2 gives the results for some selected temperatures. It has been shown for the nCB series that free molecular dipole moments ( m ) do not vary appreciably for different homologues [45,46]. So the reported m and eff values -4.9 and 4.67 D, respectively -for 7OCB [47] are taken as the values for 5OCB.…”

Section: Static Dielectric Properties Of Binary Mixtures 575mentioning

confidence: 98%

Dielectric study of nematic and induced smectic-A phases in binary mixtures of pentyloxy cynobiphenyl with threep-azoxybenzenes

Jaishi¹,

Mandal²

2005

Phase Transitions

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Static dielectric properties of 18 binary mixtures of 4,4 0 -pentyloxy cyanobiphenyl (5OCB) with 4,4 0 -bis(alkoxy)azoxybenzenes (nOAB) for n ¼ 5, 6 and 7 have been studied in detail. Seventeen mixtures show induced smectic-A (SmA) phase; a few mixtures exhibit nematic phase as well. Pure 5OCB has a large positive dielectric anisotropy while nOAB members have small but negative anisotropy. However, all the mixtures exhibit positive anisotropy. In the mixtures, except those with x 5OCB ! 0.85, the values of " k , " ? and "" " increase smoothly with temperature. The values of " iso are found to be higher than the "" " values within the mesophases, with a jump at T NI or T SI . Effective values of the dipole moments in the mixtures are found to be less than the values observed in the pure compounds. This suggests that anti-parallel homo-dimers of 5OCB exist in the mixtures as observed in the pure compound. Moreover, at the onset of SmA phase, values of " " " are found to decrease from those in the nematic phase. This implies that additional anti-ferroelectric type of ordering is developed in the induced SmA phase. In all the mixtures the anisotropy parameter Á" decreases with concentration, becomes minimum at x 5OCB ¼ 0.5, and then increases quite fast. Kirkwood correlation factors have also been calculated to find the nature and extent of the molecular associations.

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Section: Static Dielectric Properties Of Binary Mixtures 575mentioning

confidence: 98%

Dielectric study of nematic and induced smectic-A phases in binary mixtures of pentyloxy cynobiphenyl with threep-azoxybenzenes

Jaishi¹,

Mandal²

2005

Phase Transitions

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“…Surface charges may exist on these DRs, related either to the crystallographic orientation of the nanorodsurface [71] and/or to dangling bonds unsaturated by the surface ligands. [72] A symmetry breaking in the smectic phase at the DR interfacemay occur, due to the charges at the DR surface, which may orient all neighbouring 8CB molecular dipoles. [71][72] Strong electric dipolar interactions between the 8CB molecular dipoles (4.9 D) and the DR dipoles [71] maythus favour DR dipole orientationin the plane parallel to the 8CB stripes and perpendicular to the substrate.…”

mentioning

confidence: 99%

Alignment of Rod‐Shaped Single‐Photon Emitters Driven by Line Defects in Liquid Crystals

Pelliser

Manceau

Lethiec

et al. 2015

Adv Funct Materials

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We use arrays of liquid crystal defects, linear smectic dislocations, to trap semi-conductor CdSe/CdS dot-in-rods which behave as single photon emitters. We combine measurements of the emission diagram together with measurements of the emitted polarization of the single emitters. We show that the dot-inrods are confined parallel to the linear defects to allow for a minimization of the disorder energy associated with the dislocation cores. We demonstrate that the electric dipoles associated with the dotin-rods, tilted with respect to the rods, remain oriented in the plane including the smectic linear defects and being perpendicular to the substrate, most likely due to the dipole/dipole interactions between the dipoles of the liquid crystal molecules and the dot-in-rods ones. Using smectic dislocations, we can consequently orient nanorods along a unique direction for a given substrate, independently of the ligands' nature, without any induced aggregation, leading as well to a fixed azimuthal orientation for the associated dot-in-rods' dipoles. These results open the way for a fine control of nanoparticle anisotropic optical properties, in particular a fine control of single photon emission polarization.Control of single photon emitters is a major objective in the field of nanophotonics.[1] The synthesis of colloidal semiconductor inorganic nanocrystals having specific light-emission properties has been providing important advances in this field. In particular, recent developments in synthesis methodologies, fully compatible with standard nanofabrication technologies have enabled a superior 3 control on nanocrystals composition and morphology.Rod-shaped nanocrystals showing pronounced polarization, behaving as emitting linear dipoles, have been obtained. [2][3][4] The encapsulation of a spherical core into a rod-like shell [5] resulted in non-blinking inorganic single photon emitters, [6] hereafter referred to as dot-in-rods (DRs). Moreover it has been recently shown that, by increasing the thickness of the shell, it is possible to greatly suppress photoluminescence blinking and to improve DRs overall photo-stability, while keeping a low probability of multi-photon emission. [7] Such features are of primary importance when nanocrystalsare used in applications demanding a control of photons'polarization, such as coupling with complex photonic cavities [8][9] or quantum cryptography.[10] The control of the polarization of the emitted light also requires the capacity to control the particle orientation. Howevertechnologies aimed at guiding nanocrystal orientation at the single particle level are still poorly discussed in literature.Alignednanoparticleshave been obtained through mechanical rubbing, [11] short-range interactions [12][13] or patterned substrates. [14] Liquid crystal-like structures, composed of alarge number of elongated nanocrystalsassembled in multi-layers have also been evidenced on both solid substrates [15][16][17][18] and water films. [18][19][20] Orientation and positional ordering of CdS and CdSe...

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“…Given the fact that both MBBA and 5CB LCs are complex in terms of electrostatic features, we also included in the study a simpler model from 5CB series, namely cyanobiphenyl (0CB). Some details concerning the properties of these LCs are reported in other works, [30][31][32] which indicate that MBBA, 5CB, and 0CB have dipole moments of 2.32D, 6.50D, and 4.4 2D, respectively. The influence of the dianhydride moieties on the interaction ability with MBBA, 5CB, and 0CB was assessed in this work and presented in Figure 4.…”

Section: Dipole Moment and Lc Interactionmentioning

confidence: 77%

Molecular design of some semi-alicyclic polyimides as a route to improve refraction and dielectric properties for liquid crystal display applications

Barzic¹,

Albu²,

Ioanid³

et al. 2017

High Performance Polymers

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The study establishes an adequate monomer combination for achieving the best balance of properties required in obtaining polyimide alignment layers for display devices. The molecular design of some aliphatic/aromatic polyimides was performed by using dianhydride monomers with distinct configurations in terms of rigidity, size, and symmetry. The polyimides based on semi-flexible and nonsymmetric dianhydride moieties present lower refractive index and dielectric constant (<3) than those obtained from symmetric and rigid dianhydride units. This determines faster traveling of visible and microwave radiations as required for liquid crystal alignment purposes. The interactions of samples with the N-(4-Methoxybenzylidene)-4-butylaniline, cyanobiphenyl, and 4-pentyl-4-cyanobiphenyl nematics were assessed. The analyzed polyimides have higher surface tensions than the ones of the liquid crystals, determining a parallel arrangement of the nematic molecules. As the dispersive interactions at the polymer surface are lower, the work of spreading is higher as a result of improved adhesion of liquid crystal with the polyimide alignment layer. The sample containing rigid, symmetric, noncoplanar dianhydride units (PI.4) and the one based on semi-flexible, nonsymmetric dianhydride moieties are the most transparent for visible and microwave radiations, allowing low cohesion interaction at interface with nematics. These aspects recommend the two studied polyimides as candidates for alignment layers.

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Dipole Moments of 4-n Alkyl-4′-Cyanobiphenyl Molecules (from OCB to 12CB) Measurement in Four Solvents and Theoretical Calculations

Cited by 40 publications

References 15 publications

Dielectric study of nematic and induced smectic-A phases in binary mixtures of pentyloxy cynobiphenyl with threep-azoxybenzenes

Dielectric study of nematic and induced smectic-A phases in binary mixtures of pentyloxy cynobiphenyl with threep-azoxybenzenes

Alignment of Rod‐Shaped Single‐Photon Emitters Driven by Line Defects in Liquid Crystals

Molecular design of some semi-alicyclic polyimides as a route to improve refraction and dielectric properties for liquid crystal display applications

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