Cyano Biphenyl Research Articles

MD simulations of diffusion of cyanobiphenyl molecules adsorbed on the graphene surface coated with alkane and alcohol molecules

AbstractMolecular dynamics simulations were carried out to study the structural and diffusion properties of a cyanobiphenyl monolayer composed of pentyl cyano biphenyl (5CB) and pentyloxy cyano biphenyl (5OCB) molecules on a graphene surface coated with alkane and alcohol molecules. To investigate the diffusion properties of 5CB and 5OCB molecules on the graphene surface, the molecules of pentane ( ) and dodecane ( ) from alkanes and dodecanol ( ) from alcohols with a polar hydroxyl ( ) terminal functional group were chosen as orienting surfactant molecules. It was found that the diffusion ability of cyanobiphenyl molecules in a graphene substrate coated with alkane and alcohol molecules depends on the chain length of these molecules and on the presence of polar hydroxyl –OH terminal groups. With an increase in the length of alkane molecules from to , the value of the diffusion coefficient (or ), it decreases slightly, while the presence of the polar hydroxyl terminal group leads to a significant decrease in this diffusion coefficient of cyanobiphenyl molecules.

Coumarin Schiff base derivatives with terminal cyano group: Synthesis, Mesomorphic properties and DFT investigation

Coumarin Schiff base derivatives with terminal cyano group were synthesized and analysed for their mesomorphic behaviour. The homologous series CN6–16 (n = 6,8,10,12,14,14,16) with 4-cyano benzaldehyde, lower member (n = 6,8) exhibited enantiotropic nematic mesophase, while smectic A mesophase started appearing with n = 8 during cooling process. Enantiotropic smectic A mesophase was observed with higher chain length n = 10,12,14,16. Similar trend of mesomorphic properties was exhibited by Schiff base derivatives BPCN8–14. Introduction of cyano biphenyl at aldehyde end of the molecule has led to formation of stable smectic A mesophase as compared to that by compounds CN8–14. Introduction of ester linkage in Schiff based derivatives, compounds ECN10–12 and RECN10–12 showed smectic A mesophase with high clearing temperature. VT-XRD analysis of two compounds has confirmed orthogonal smectic A mesophase. Additionally, DFT calculations were carried out for all the newly synthesized compounds and compared with similar literature molecules for various structural and electronic parameters followed by their correlation with the mesophase type and stability.

Structural properties of a cyanobiphenyl monolayer on the graphene surface coated with alkane and alcohol molecules as seen from MD simulations

Molecular dynamics simulations were carried out to study structural properties of a cyanobiphenyl monolayer composed of pentyl cyano biphenyl (5CB) and pentyloxy cyano biphenyl (5OCB) molecules on a graphene surface coated with alkane and alcohol molecules. The molecules of dodecane, hexadecane, and dodecanol were chosen as orienting surfactant molecules. In order to investigate the structural properties, as well as the alignment of the cyanobiphenyl monolayer on the graphene surface coated with alkane and alcohol molecules, not only the numerical density profiles of these systems, but also the radial distribution functions, and the tilt angle of the liquid crystal molecules, were calculated. In order to understand the effect of the polar hydroxyl functional group on 5CB and 5OCB molecules deposited on the graphene surface, alcohols were chosen as surfactant molecules.

Amplified spontaneous emission from a liquid crystalline phase: anisotropic property and active modulation.

Amplified spontaneous emission (ASE) is considered to be a primary indication of optical gain in active media without an external resonator. Molecular materials with ASE are expected to be one of the suitable light sources for specific applications such as optical coherent tomography owing to their low coherence and flexible tunability. Concentration quenching of emissive excited states has been a critical issue to boost the quantum efficiency of molecular materials in their condensed phases. The rod-like design of molecules with excited state intramolecular proton transfer (ESIPT) has been demonstrated to overcome this issue in highly-concentrated molecularly-doped systems, as represented by C4alkyne-HBT (2-(4-(1-hexynyl)-2-hydroxyphenyl)-benzothiazole). We designed an ESIPT molecule-doped liquid crystalline (LC) system for optical amplification via the ASE regime with its wide tunability of emission intensity. Detailed ASE behaviour and optical gain of a LC blend of C4alkyne-HBT and 4-pentyl-4'-cyano biphenyl (5CB) was evaluated to afford a maximum optical gain of 16.5 cm-1 with an estimated ASE threshold of optical pumping at 0.6-0.7 mJ cm-2. Although most ASE studies focus on homogeneous solutions, solids, or crystalline states, ASE from a soft-flexible LC phase is quite limited and advantageous for the design of an external optical resonator/cavity structure. Optical excitation parallel and perpendicular to the director resulted in the strong modulation of the ASE. By using the benefits of a LC phase, the ASE was actively modulated under the external electric field by the reorientation of the molecular dipole moment.

Odd-even effect in chiral side-chain cyanobiphenyl block copolymer assemblies prepared by polymerization-induced chiral self-assembly.

The precise control of the chirality of polymer assemblies is a challenge faced by scientists and has received significant attention in recent years. In this study, we employed the polymerization-induced chiral self-assembly (PICSA) method to create chiral side-chain cyanobiphenyl (CB) block copolymer (BCP) assemblies. The flexible spacers in chiral CB monomers were regulated to exhibit two distinct odd-even effects in the supramolecular asymmetrical arrangement of the CB mesogens inside BCP assemblies. The research results indicated that the liquid crystalline properties of CB mesogens significantly influence the magnitude and sign of their chiroptical properties. These findings have significant implications for the design of polymer assemblies with designable chiroptical functions.

Supramolecular copolymerization of hydrophobic and hydrophilic monomers in liquid crystalline media.

In the case of covalent polymers, immiscible polymers can be integrated by covalently linking them together, but such a strategy is not possible in supramolecular polymers. Here we report the supramolecular copolymerization of two porphyrin-based monomers, C10P2H and TEGPCu with side chains bearing cyanobiphenyl (CB) groups at the ends of hydrophobic alkyl or hydrophilic tetraethylene glycol chains, respectively. These monomers undergo self-sorting supramolecular polymerization in highly diluted solutions ([monomer] = 3.4 × 10-9 mol% (2.0 × 10-8 mol L-1)) in nonpolar media due to the incompatibility of the side chains. Surprisingly, these monomers undergo supramolecular copolymerization under high concentration conditions ([monomer] = 7.7 mol%) in the medium of 4-cyano-4'-pentyloxybiphenyl (5OCB) to form a columnar liquid crystalline phase under thermodynamic conditions, where the individual columns are composed of supramolecular block copolymers. The combination of CB ends of both monomers and the 5OCB medium is essential for the two monomers to form an integrated structure in a condensed system without phase separation.

Design of 5CB liquid crystal antenna for tunable microwave frequency applications

ABSTRACT Cyanobiphenyls (CBs) are a class of molecules with unique properties that make them highly versatile in various fields. Their anisotropic nature, low viscosity, and sensitivity to external stimuli make them ideal for applications in display technology, photonic devices, sensors, and in tunable antennas. In this article, we present the design and simulation of a 5CB LC antenna for tunable microwave frequency applications due to its fast response time and low dielectric loss than other CB materials. The proposed antenna contains two glass substrates with an air gap of 0.004 mm between them. The lower glass contains a size of 20 × 15 mm2, while the upper glass contains a size of 13 × 15 mm2. The proposed antenna produces two bands when there is an air gap between the glass plates; three bands when diodes are used for the radiating patch; and four bands when 5CB LC material is introduced between the glass plates as a dielectric medium. The same structure produces various frequency bands, which is a notable advantage compared to the existing state of the art. All the results shown in this manuscript were simulated and measured with the body of data available from the literature.

Mesomorphic and computational evaluation of C[tbnd]N‧‧‧I halogen bonded complexes of 4-alkoxy-4′-cyanobiphenyls systems with 1,6- diiodoperfluorohexane

Thermotropic halogen bonded (XB) liquid crystalline complex (A-n XB) of 4-alkoxy-4′- cyano biphenyls (A-n) systems containing nitrile (-CN) group with variable alkoxy chain length (-CnH2n+1, where n = 3 to 10) acting as halogen bond acceptor with 1,6-diiodoperfluorohexane, (I-atom) acting as halogen bond donor were prepared by the liquid-assisted grinding method. The A-n XB complex formations, through CN‧‧‧I XB interactions, were established by the FTIR, Raman, PXRD, polarizing optical microscope (POM) with hot stage, DSC and TGA techniques. Further, POM study of these homologous XB complex series showed liquid crystalline phases with a alteration of (1–10 °C) compared to their respective parent mesogenic molecules. The computational study was carried out using Frontier Molecular Orbitals (FMOs), Molecular Electrostatic Potential (MEP), Non-covalent interactions (NCI) and Quantum theory of atoms in molecule (QTAIM) analysis to evaluate the reactivity parameters and strength of XB in the complexes.

Twist–Bend Nematic Phase Behavior of Cyanobiphenyl-Based Dimers with Propane, Ethoxy, and Ethylthio Spacers

The twist–bend nematic (NTB) phase is a liquid crystal (LC) phase with a heliconical structure that typically forms below the temperature of the conventional nematic (N) phase. By contrast, the direct transition between the NTB and isotropic (Iso) phases without the intermediation of the N phase rarely occurs. Herein, we demonstrate the effects of linkage type (i.e., methylene, ether, and thioether) on the typical Iso–N–NTB and rare direct Iso–NTB phase-transition behaviors of cyanobiphenyl (CB) dimers CB3CB, CB2OCB, and CB2SCB bearing three-atom-based propane, ethoxy, and ethylthio spacers, respectively. In our previous study, CB2SCB exhibited the monotropic direct Iso–NTB phase transition. In this study, we report that CB3CB also shows the direct Iso–NTB phase transition, whereas CB2OCB exhibits the typical Iso–N–NTB phase sequence with decreasing temperature. The Iso–LC (Iso–NTB or Iso–N) phase-transition temperatures upon cooling show the order CB2OCB (108 °C) > CB3CB (49 °C) > CB2SCB (43 °C). The thioether-linked CB2SCB is vitrifiable, whereas CB3CB and CB2OCB exhibit strong crystallization tendencies. The phase-transition behaviors are also discussed in terms of the three bent homologous series with different oligomethylene spacers n: CBnCB, CBnOCB, and CBnSCB.

Molecular Dynamics Simulations on the Flow Behavior of 5CB Liquid Crystal Sandwiched Between Iron Walls

AbstractThe 4‐n‐pentyl‐4′‐cyano biphenyl (5CB) liquid crystal (LC) sandwiched and sheared between atomically flat and grooved iron walls, respectively, is simulated using molecular dynamics, and the flow behavior of the system under confinement, pressure, and shear is investigated. The order parameter P2, velocity, and density of 5CB are profiled as a function of distance from the walls using a block analysis method. The flow‐alignment phenomenon is reproduced, and alignment angles ranging from 11.3° to 13.9° are observed. The competition between the elastic effect of the surface and viscous effect of the flow on the orientation of the 5CB molecules is investigated. The P2 of 5CB located in the vicinity of the grooved walls is higher than that of the flat walls, while this difference is negligible in the case of 5CB distanced from the walls. Instead of boundary slip or Couette flow, the velocity profiles reveal a boundary condition (BC) of central localization, which is very different from the assumed Couette flow BC in most analytical models of LC flow. This work enhances the current molecular‐scale understanding of the flow behavior of confined liquid crystals and provides additional insights into the phenomenon.

Tribological properties of laser surface texturing modified GCr15 steel under graphene/5CB lubrication

Dimple-textured surfaces of square arrays with different geometrical parameters (area density, diameter and depth) were prepared on the surface of GCr15 steel. The friction and wear experiments were carried out under the lubrication of Suspension of graphene and liquid crystal 4-n-pentyl-4'-cyano biphenyl (5CB). By controlling the area density, diameter and depth of the dimples, the lubrication performance of laser surface texturing under the condition of starved lubrication was analyzed, and the reducing friction and wear resistance mechanism of laser surface texture was preliminarily discussed. The lubrication performance of the dimple-textured surface is best when the depth of the dimple is 10 μm, the area density is 8%, and the diameter is 100 μm. The friction coefficient at this textured parameter is 0.031, which is a 32.6% decrease compared to the untextured surface (0.046). The reduction friction mechanism of the textured surface is mainly to improve load-bearing capacity, store lubricant, reduce contact area and secondary lubrication. Meanwhile, XPS analysis shows that during the friction, the graphene/5CB suspension has a tribochemical reaction in the textured surface, and a chemical reaction film is formed on the steel surface. The research results can provide theoretical guidance for the optimization of texture geometric parameters under different application conditions.

Copper Iodide Clusters Coordinated by Emissive Cyanobiphenyl-Based Ligands.

Copper(I) halides are currently the subject of intensive research because of their rich photophysical properties combined with economic and eco-friendly advantages for practical applications. The molecular copper iodide cluster of the general formula [Cu4I4L4] (L = ligand) is a well-known photoluminescent compound, and the possibility to enlarge the panel of its photophysical properties is studied here, by exploring ligands bearing a distinct emitter. The comparative study of five copper iodide clusters coordinated by different phosphine ligands functionalized by the emissive cyanobiphenyl (CBP) group is thus described in this work. The emissive properties of the ligands have a great impact onto the photophysical properties of the cluster. Compared with classical [Cu4I4L4] copper iodide clusters, the origin of the emission bands is largely modified. The CBP moiety of electron acceptor character significantly lowers in energy the vacant orbitals and consequently affects the global energetic layout. These clusters present dual emission based on two different emissive centers which interplay through energy transfer. This study demonstrates that the design of original ligands is an effective approach to enrich the photophysical properties of the appealing family of copper halide complexes.

Formation of Self-organized Structures of Hybrid Amorphous Materials Based on Polyhedral Silsesquioxanes

The formation of self-organized structures of organic-inorganic hybrid amorphous molecules based on polyhedral silsesquioxanes (POSS) is reported. The hybrid materials were synthesized using POSS as the inorganic core and cyanobiphenyl (CBP) as the organic substituent. The type of structure formed depends on the length of the alkyl spacer used to connect the POSS and CBP groups. The hybrid amorphous material with an alkyl spacer consisting of eleven methylene units resulted in Voronoi-like dot patterns, the size of which are easily controlled by varying the thickness of the initial films.

Estimation of absorption spectral shifts of cyano biphenyl liquid crystals: An impact of different solvents and oxygen substitution

Two nematic liquid crystals, viz. 4-octyl-4׳-cyanobiphenyl (CBP8) and 4-octyloxy-4׳-cyanobiphenyl (OCBP8) have been studied using CNDO/S and INDO/S approaches. The impact of different solvents (benzene, chloroform), and oxygen substitution on electronic origins of shifts in wavelengths have been summarized. The substituent and solvents induced shifts of the molecules in absorption maxima, extinction coefficient, and energy band gap have been analyzed. The changes in photosensitivity and conductivity of these compounds from the view point of these shifts have been analyzed. Other parameters such as ionization potential, chemical potential, electron affinity, electro negativity, hardness, softness of the molecules have also been reported. The solvent-specific alteration of optical and electro chemical properties have been discussed for wavelength tunable device and light modulation applications.

Remarkable Increase of Fluorescence Quantum Efficiency by Cyano Substitution on an ESIPT Molecule 2-(2-Hydroxyphenyl)benzothiazole: A Highly Photoluminescent Liquid Crystal Dopant

Fluorescent molecules with excited-state intramolecular proton transfer (ESIPT) character allow the efficient solid-state luminescence with large Stokes shift that is important for various applications, such as organic electronics, photonics, and bio-imaging fields. However, the lower fluorescence quantum yields (ΦFL) in the solution or viscous media, due to their structural relaxations in the excited state to reach the S0/S1 conical intersection, shackle further applications of ESIPT-active luminophores. Here we report that the introduction of a cyano group (-CN) into the phenyl group of 2-(2-hydroxyphenyl)benzothiazole (HBT), a representative ESIPT compound, remarkably increase its fluorescence quantum yield (ΦFL) from 0.01 (without -CN) to 0.49 (with -CN) in CH2Cl2, without disturbing its high ΦFL (=0.52) in the solid state. The large increase of the solution-state ΦFL of the cyano-substituted HBT (CN-HBT) is remarkable, comparing with our previously reported ΦFL values of 0.05 (with 4-pentylphenyl), 0.07 (with 1-hexynyl), and 0.15 (with 4-pentylphenylethynyl). Of interest, the newly-synthesized compound, CN-HBT, is miscible in a conventional room-temperature nematic liquid crystal (LC), 4-pentyl-4′-cyano biphenyl (5CB), up to 1 wt% (~1 mol%), and exhibits a large ΦFL of 0.57 in the viscous LC medium. A similar ΦFL value of ΦFL = 0.53 was also recorded in another room-temperature LC, trans-4-(4-pentylcyclohexyl)benzonitrile (PCH5), with a doping ratio of 0.5 wt% (~0.5 mol%). These 5CB/CN-HBT and PCH5/CN-HBT mixtures serve as light-emitting room-temperature LCs, and show anisotropic fluorescence with the dichroic ratio of 3.1 upon polarized excitation, as well as electric field response of luminescence intensity changes.

Thermoresponsive Reflective Scattering of Meso-Scale Phase Separation Structures of Uniaxially Orientation-Ordered Liquid Crystals and Reactive Mesogens.

Polymer network liquid crystals (PNLCs) capable of thermoresponsive change in reflective scattering were fabricated using a self-organization technique called photopolymerization-induced phase separation. These PNLCs exhibit nonscattering states at temperatures τ below the nematic-to-isotropic (NI) phase transition temperature τNI but reflective scattering states at τ values above τNI. The magnitude of change of optical clarity is 80% and of solar transmittance is 20% in PNLCs with a thickness of 50 μm. The microscopic structures consist of wavelength- or meso-scale phase separation domains of liquid crystals (LCs) and polymerized reactive mesogens (RMs) in which cyanobiphenyl (CB) groups are thermoresponsively transformed between uniaxially orientation-co-ordered and disordered states. Such thermoresponsive structures were fabricated by employing the CB groups as mesogenic bodies, which were expected to mutually associate due to their physicochemical structures. Cross-linkers stabilized the meso-scale domains and made the PNLCs durable through repeated temperature changes. Polarizing optical microscopy (POM) and scanning electron microscopy showed meso-scale composites that reflectively scatter visible and near-infrared light. POM and Fourier-transform infrared spectroscopy at different temperatures suggest that the orientation order of the CB groups changes in the LC phase in response to temperature but remains ordered in the RM phase. Such a thermoresponsive change in the orientation order produces the switchability in meso-scale nonuniformity and consequently in reflective light scattering. The thermoresponsive PNLCs are not only effective as energy-saving smart windows but also advantageous at stages of manufacture, installation, and operation.

Electro-Optical Parameters with Adverse Order of 10CB Liquid Crystal Molecules Studied under the Influence of an External High Electric Field: A Theoretical Approach

Abstract: The 10CB liquid crystal (LC) at the higher electric field has a negative-order parameter. The 10CB LC has a definite order that maintains smectic phase stability. 10CB LC has supported the isotropic phase stability at an elevated external electric field and exhibited an unfavorable orientation of the order parameter. At the more upper electric field, the director angle (θ) fluctuated and contained θ less than 90°. The negative orientation of the order parameter and the large absorption anisotropy enhanced the optical birefringence with a reversal of sign. The negative-order parameter responsible for the IR absorbance has increased instead of reduction. The 10CB liquid crystal is a member of the cyano biphenyl series; therefore, the dipolar strength is maximum contributed to by the C-H atom asymmetric stretching of the alkyl chain length. The 10CB LC has a large bandgap (3.60 eV). Keywords: 10CB, Electric field, Electro-optical effect, Spectroscopy, Density functional theory (DFT).

Influence of multifluorophenyloxy terminus on the mesomorphism of the alkoxy and alkyl cyanobiphenyl compounds in search of new ambient nematic liquid crystals and mixtures

ABSTRACT A series of cyanobiphenyl (CB) and cyano-p-terphenyl (CT) derivatives containing a variety of highly fluorinated aryloxyl termini and different connecting bridges were efficiently synthesized via aromatic nucleophilic substitution (SNAr) and their mesogenic properties described. Comparison with the non-fluorinated analogues indicates that the terminal multifluoroaryloxy group generally decreases the crystal to nematic phase transistion temperature and enhances the supercooling of these mesogens. Furthermore, several binary LC mixtures formed by the multifluoroaryloxy tail-terminated compounds were found exhibiting promising wide room temperature nematic phases ranges comparable to the commercial quaternary mixture E7. Our binding free energy (GBE) calculations predict that the fluorinated aryloxy terminated molecules tend to assume homeotropic orientation on Al(ClO4)3 and Ni(ClO4)2 metal salt decorated surfaces, which is consistent with the observed anchoring behavior. As such, these materials are promising candidates for chemoresponsive sensor devices which display a rapid response to a variety of analytes.

Hybrid Nanosystems Based on Metal-Containing Mesogenic CyanoAlkyl and Alkoxybiphenyls

The paper reviews the results of the authors on the production of hybrid nanosystems based on liquid crystalline (LC) long-chain cyano(alkyl and alkoxy)biphenyls (5CB, 5OCB, and 8CCB) including nanosized metal species. The samples were obtained through the direct incorporation of metal (silver and copper) atoms and small clusters into mesogenic CB matrices via a low temperature co-condensation technique, and the formation of biligand metal complexes were revealed by FTIR and ESR-spectroscopy. The heating of the systems led to the controlled growth of metal clusters and nanosized metal particles of the definite size beginning from 1 up to 200 nanometers, and their highly-ordered assemblies stabilized in the solid and liquid crystalline phases. It is shown that supramolecular ordering in different LC phases of cyanobiphenyl matrices determines the size and shape of nanosized metal species that are formed in the systems under investigation, as well as the morphology of their aggregates. TEM and atomic force microscopy (AFM) data revealed the existence of orientationally-ordered nanostructures in the nematic phases of 5CB and 5OCB. The growth of quasi-fractal 2D-aggregates was shown for layer-structured smectic mesophase of 8CB. The UV–Visible spectra of hybrid metal–mesogenic nanosystems Ag-5CB and Cu-5CB that were incorporated into polymeric films revealed intensive plasmonic bands at 400–450 nm, similar to silver nanoparticles, and 540–650 nm, similar to copper nanoparticles. The increasing of the metal contents in the samples caused the growth of highly anisometric shaped metal rods, with the ratio of the length to the diameter being more than 10 and plasmonic bands at region of λ ≥ 650 nm.

Surface anchoring behavior of 5CB liquid crystal confined between iron surfaces: A molecular dynamics study

To examine the anchoring behavior of 4-n-pentyl-4′-cyano biphenyl (5CB) liquid crystal (LC) on iron surfaces, united-atom molecular dynamics simulations were performed with a ~12 nm 5CB film composed of 1000 molecules under confinement between both the atomically-flat surfaces and sinusoidal grooved surfaces. The order parameter of 5CB is enhanced by the grooved surfaces, but diminished by the flat one. In both cases, 5CB molecules away from surfaces tend to align parallel to surfaces and along a certain direction. However, for the 5CB near surfaces, the flat surface yields a random planar anchoring and the grooved surface induces a unidirectional planar anchoring. The diffusion slows down when 5CB is confined between surfaces and the slowing down is mainly concentrated near surfaces, making 5CB solid-like. For the 5CB away from surfaces, the flat surface slows down the diffusion, while the grooved surface accelerates the diffusion, especially along the groove (and the director n) direction. The results provide a full description of the iron-LC interactions at the nanoscale and are important for the understanding of LC behaviors anchoring on surfaces with different morphologies.