Cyanobiphenyl Liquid Crystals Research Articles

Control Patterning of Cyanobiphenyl Liquid Crystals for Electricity Applications.

Controlling molecular self-assembly from organic solution evaporation is an important strategy for developing many functional materials and systems. In this work, it is demonstrated that 4-octyloxy-4'-cyanobiphenyl (8OCB) liquid crystals can be patterned into well-oriented stripes with very high micrometer-scale precision using a sandwich system through a dewetting method. The preparation temperature, concentration, and surface energy are combined to control the morphology and orientation of 8OCB microstripe arrays assisted by silicon micropillars. Microstripes prepared below the isotropic temperature were uniform, well-ordered, and showed high electricity. In addition, 8OCB molecules have a strong tendency toward antiparallel alignment, nearly standing up on the substrate with long axes parallel to the microstripe. Also, we point out the mechanism for the self-assembly process of 8OCB on the air-liquid and liquid-solid surface.

Thermal and electric field effects on the nonlinear optical response of a cyanobiphenyl liquid crystal doped with carbon dots

The present study is devoted to the investigation of the nonlinear optical response of a cyanobiphenyl liquid crystal (8CB) doped with carbon dots derived from dansyl chloride (CD-DsCl). Using the time-resolved z-scan technique, it is investigated how the CD-DsCl addition affects the nonlinear refractive coefficient of planar liquid crystal samples. The temperature dependence of nonlinear optical responses of pristine and doped samples are analyzed close to smectic-A - nematic and nematic - isotropic phase transitions. Furthermore, the effects of an external electric field are analyzed. Our results show that doped 8CB samples may exhibit an enhanced nonlinear optical response, which depends on the strength of the external field.

Exploring the Impact of Intermolecular Interactions on the Glassy Phase Formation of Twist-Bend Liquid Crystal Dimers: Insights from Dielectric Studies

The formation of the nematic to twist-bend nematic (NTB) phase has emerged as a fascinating phenomenon in the field of supramolecular chemistry, based on complex intermolecular interactions. Through a careful analysis of molecular structures and dynamics, we elucidate how these intermolecular interactions drive the complex twist-bend modulation observed in the NTB. The study employs broadband dielectric spectroscopy spanning frequencies from 10 to 2 × 109 Hz to investigate the molecular orientational dynamics within the glass-forming thioether-linked cyanobiphenyl liquid crystal dimers, namely, CBSC7SCB and CBSC7OCB. The experimental findings align with theoretical expectations, revealing the presence of two distinct relaxation processes contributing to the dielectric permittivity of these dimers. The low-frequency relaxation mode is attributed to an “end-over-end rotation” of the dipolar groups parallel to the director. The high-frequency relaxation mode is associated with precessional motions of the dipolar groups about the director. Various models are employed to describe the temperature-dependent behavior of the relaxation times for both modes. Particularly, the critical-like description via the dynamic scaling model seems to give not only quite good numerical fittings, but also provides a consistent physical picture of the orientational dynamics in accordance with findings from infrared (IR) spectroscopy. Here, as the longitudinal correlations of dipoles intensify, the m1 mode experiences a sudden upsurge in enthalpy, while the m2 mode undergoes continuous changes, displaying critical mode coupling behavior. Interestingly, both types of molecular motion exhibit a strong cooperative interplay within the lower temperature range of the NTB phase, evolving in tandem as the material’s temperature approaches the glass transition point. Consequently, both molecular motions converge to determine the glassy dynamics, characterized by a shared glass transition temperature, Tg.

Influence of electric field on the electro-optical and electronic properties of 4-n-alkoxy-4$$^\prime $$-cyanobiphenyl liquid crystal series: An application of DFT

Influence of electric field on the electro-optical and electronic properties of 4-n-alkoxy-4$$^\prime $$-cyanobiphenyl liquid crystal series: An application of DFT

Conformation-dependent molecular association and spectral properties of 4-pentyl-4′-cyanobiphenyl liquid crystal in different phases

The 4-pentyl-4′-cyanobiphenyl (5CB) molecule conformation and structure alignment have been investigated by means of temperature variable Fourier transform infrared (FTIR) and photoluminescence (PL) spectroscopy in a wide temperature range (from −90 to 50 °C) covering the 5CB glass-like, metastable and stable crystalline, nematic and isotropic phases defined by differential scanning calorimetry measurements. The corresponding FTIR absorption and PL emission bands reflect a strong dipolar association and a formation of at least two types of 5CB dimeric structures with antiparallel or parallel orientation in the planar configuration. No formation of hydrogen bonds between the cyano groups and hydrogen atoms of the adjacent benzene ring has been found. Besides, a small amount of the 5CB monomer structure has been shown to be present in all phases. The observed temperature-induced changes in the IR and PL spectra can be used as an independent source of experimental information on conformational equilibria and structure alignment of 5CB in different states under the phase transitions.

Molecular Polarizability Studies on 12. CB, 7O. CB Cyano-biphenyl Liquid Crystal by Theoretical and Experimental Approach

Molecular Polarizability Studies on 12. CB, 7O. CB Cyano-biphenyl Liquid Crystal by Theoretical and Experimental Approach

Magnetic field induced Fréedericksz transition in a system of ultrafine spherical [formula omitted] nanoparticles doped 7CB media

In this work, experimental studies of electrically and magnetically induced re-orientational transitions in suspensions of cobalt ferrite (CoFe2O4) nanoparticles in 7CB (4-n-heptyl-4'-cyanobiphenyl) liquid crystal (LC) are presented. Two concentrations are studied (i.e 0.033wt% or sample A and 0.044wt% or sample B). The results obtained are compared with the pristine liquid crystal. Low threshold voltages and magnetic fields for the re-orientational transition are observed in the doped cases. The nanoparticles bonded to the LC in close proximity are orienting in a parallel manner with the bulk liquid crystal media and causing these changes. Effect of the polarity and position of the magnet on the re-orientational mechanism in comparison to the pristine sample is also studied.

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.

Nanoscale Events on Cyanobiphenyl-Based Self-Assembled Droplets Triggered by Gas Analytes.

Liquid crystals (LCs) are prime examples of dynamic supramolecular soft materials. Their autonomous self-assembly at the nanoscale level and the further nanoscale events that give rise to unique stimuli-responsive properties have been exploited for sensing purposes. One of the key features to employ LCs as sensing materials derives from the fine-tuning between stability and dynamics. This challenging task was addressed in this work by studying the effect of the alkyl chain length of cyanobiphenyl LCs on the molecular self-assembled compartments organized in the presence of ionic liquid molecules and gelatin. The resulting multicompartment nematic and smectic gels were further used as volatile organic compound chemical sensors. The LC structures undergo a dynamic sequence of phase transitions, depending on the nature of the LC component, yielding a variety of optical signals, which serve as optical fingerprints. In particular, the materials incorporating smectic compartments resulted in unexpected and rich optical textures that have not been reported previously. Their sensing capability was tested in an in-house-assembled electronic nose and further assessed via signal collection and machine-learning algorithms based on support vector machines, which classified 12 different gas analytes with high accuracy scores. Our work expands the knowledge on controlling LC self-assembly to yield fast and autonomous accurate chemical-sensing systems based on the combination of complex nanoscale sensing events with artificial intelligence tools.

Engineering mesophase stability and structure via incorporation of cyclic terminal groups

The installation of an aliphatic ring at the end of the alkyl chain for a family of 4-alkoxy-4′-cyanobiphenyl liquid crystals is shown to enhance clearing points and promotes the formation of smectic phases, relative to the linear parent materials.

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.

Dielectric and electro-optical properties of ferric oxide nanoparticles doped 4-octyloxy-4’ cyanobiphenyl liquid crystal-based nanocomposites for advanced display systems

ABSTRACT Doping of ferric oxide (Fe2O3) nanoparticles in 4-octyloxy-4ʹ cyanobiphenyl (8OCB) liquid crystal compound embedded in sample cells formed by photolithographic technique. The dielectric spectroscopy is investigated over a wide frequency from 500 Hz to 10 MHz. Various parameters such as switching time (τon and τoff), dielectric permittivity (ε’), dielectric loss (ε”), relaxation frequency and optical texture of pristine 8OCB and 8OCB-Fe2O3 nanocomposite were investigated as functions of frequency and temperature. Moreover, splay elastic constant (k11), rotational viscosity (γ) as a function of weight % of Fe2O3 NPs have also been investigated. These values are strongly affected by the presence of Fe2O3 NPs due to the enhancement of molecular ordering. The doped Fe2O3 NPs within the 8OCB LC may align along the director ñ strongly favours a splay distortion of ñ as the orientational order is increased. Optical image showed an improved molecular ordering of 8OCB with doping of Fe2O3 NPs. The dielectric anisotropy (Δε) of 8OCB-Fe2O3 nanocomposites was found to be reduced whereas threshold voltage (Vth) increased with increasing the doping of Fe2O3 NPs within the 8OCB. In addition to this, Fe2O3 NPs alter the magnitude of the perpendicular and parallel component of dielectric permittivity of nanocomposite.

Carbosilane terminated alkoxycyanobiphenyls for bistable scattering mode LCDs

We report the synthesis and characterisation of a family of cyanobiphenyl liquid crystals with varying alkyl chain length and a carbosilane terminal group, and demonstrate their use in ion doped SmA scattering devices.

Photoluminescence modulation in the graphene oxide dispersed 4-n-octyl-4’-cyanobiphenyl molecular system

Herein, we investigate the mechanism of photoluminescence modulation (PLM) in the 4-n-octyl-4’-cyanobiphenyl liquid crystal (8CB LC) in the presence of various doping concentrations (0.02 to 0.4 wt%) of 2D-GO (two-dimensional graphene oxide) nanoflakes. The role of intermolecular interactions on PLM and the subsequent effect on the decay lifetime is also examined via time-resolved PL measurements. The presence of intermolecular interactions is additionally confirmed by means of differential scanning calorimetry and polarized optical microscopy. The successive addition of GO nanoflakes sharpens the absorption band of pure 8CB LC; consequently, it is blue shifted. The PL properties of the 8CB LC enhance due to the addition of GO nanoflakes which might be attributed to electron–phonon interaction between 8CB molecules and GO nanoflakes. The PL enhancement has been further supported by the time-resolved PL decay time measurement. The longest and shortest fluorescence lifetimes have been recorded for the 0.1 and 0.4 wt% GO/8CB composites, respectively. The investigated composites have shown their potential applications for fluorescent optical devices; however, the quantum efficiency needs to be further improved.

Highly Ordered Methacrylate Block Copolymers Containing Liquid Crystal Side Chains

Block copolymers composed of cinnamate or biphenyl liquid crystal and fluorinated side chain blocks were synthesized by RAFT polymerization. The block copolymers (BCPs) showed sharp phase separation benefit from the chemistry incompatibility of the fluorinated and the liquid crystal blocks. Both cinnamate and cyano-biphenyl liquid crystal containing BCPs formed highly ordered nanostructures with domain-spacing ranged from 15.6 nm to 12.4 nm. UV exposure could alter the cinnamate containing domain morphology via partially dimerization.

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.

Physico-chemical properties, frontier orbitals and spectral study of a nematogen: 4-n-ethoxy-4'-cyanobiphenyl and its two constituents

Benzonitrile and ethoxybenzene are the two main building blocks of 4-n-ethoxy-4'-cyanobiphenyl (2OCB) liquid crystal (LC), which is a member of 4-n-alkoxy-4'-cyanobiphenyl LC homologous series. The 2OCB transforms to isotropic liquid at 102.0 °C and exhibits nematic LC phase at 90.5 °C. In present investigation, 4-n-ethoxy-4'-cyanobiphenyl (2OCB) and its two constituent molecules namely benzonitrile and ethoxybenzene have been undertaken. Electronic structure, thermodynamic properties and spectral analysis of 2OCB, benzonitrile and ethoxybenzene have been examined by DFT-B3LYP/6-31G(d,p) technique with GAMESS program. The dipole moment, frontier orbitals energy, entropy, enthalpy, internal energy and Gibb’s potential are obtained. Electronic, spectral and other physico-chemical properties of 2OCB nematic LC molecule and its two constituents are elaborated.

Fluorescence of molecular composites that consist of nematic liquid crystal and merocyanins

Background: Considered merocyanine molecules have donor D and acceptor A moieties connected by polymer chain. The conjugated donor D and acceptor A parts of merocyanine molecules are planar in the ground state. The D-π-A molecular complexes can change their conformations in an excited state due to cis-trans-conformational transitions. The viscosity of the solvent affects conformational changes, photoluminescence (PL) decay and PL lifetime. Therefore the PL of merocyanine molecules strongly depends on medium in excited and ground states. A nematic liquid crystal was utilized as a solvent for merocyanine molecules since it is characterized by long range order, orientates merocyanine molecules along its axis and is sensitive to external electro-magnetic field. The molecules with conjugated donor D and acceptor A parts are promising for molecular electronics (instruments for recording and processing information), optoelectronics (laser technologies) and biological research (fluorescent probes like prominent thioflavin T), since their PL essentially depends on the nature of the environment. Objectives: The main objective of this paper is to investigate and explain impact of liquid crystal medium on considered molecules. Also influence of molecular conformational changes on their spectral properties is considered. Materials and Methods: Two types of merocyanine molecules M-1 and M-2 were investigated. The spectral properties of molecules in different organic solvents such as acetonitrile, toluene, glycerol, and in 4-pentyl-4′-cyanobiphenyl (5CB) liquid crystal were compared. Stationary and time-resolved emission spectra of molecular merocyanine solutions were used to investigate conformational changes of molecules. To determine a lifetime of molecular excited states, a technique of Time Correlated Single Photon Counting with picosecond resolution in time was used. Results: The results indicate that optical properties strongly depend on conformation of conjugated donor-π-acceptor compounds. A relaxation of dye molecules to the ground state is accompanied by conformational changes. The quantum yield and lifetime of PL increase in more viscous solvents. The liquid crystal made conformational changes of considered molecules in ground and excited states. Conclusions: Analysis of the results serves as a basis for constructing a theory that explains properties of D-π-A molecular compounds under optical excitation. The molecular pairs are formed by merocyanine and liquid crystal molecules. The liquid crystal molecule defines conformation of merocyanine molecule in a pair. Moreover, both types of merocyanine molecules in liquid crystal have the same conformation. This hypothesis explains similarities of optical properties of M-1 and M-2 molecules in liquid crystal.

Experimental analysis of lateral thermal inhomogeneity of a specific chip-calorimeter sensor

Fast scanning calorimetry (FSC) requires reliable temperature measurements and knowledge about the temperature distribution in the chip calorimeter sensor. Analysis of the melting temperature of indium placed at different positions on the sensor and thermo-optical analysis of the isotropization of 4,4′-octyloxy cyanobiphenyl (8OCB) liquid crystal allow estimation of the lateral temperature distribution of chip calorimeter sensors. The chip sensor UFS 1 (Flash DSC1™, Mettler Toledo, Switzerland) was chosen as an example but the procedures described also hold for other sensors. The data revealed on one side existence of distinct hot- and cold-spots and on the other side an area with a rather homogeneous temperature distribution. The latter, central area of the sensor is recommended for placing samples if precise measurement of transition temperatures are anticipated. The observed inhomogeneous temperature distribution over the total sensor area is confirmed by thermo-optical analysis of melting of poly (l-lactic acid) and crystallization of isotactic polypropylene, emphasizing the need for careful sample preparation/positioning in typical fast scanning chip calorimeter analyses.

Phase-sensitive lock-in detection for high-contrast mid-infrared photothermal imaging with sub-diffraction limited resolution.

Imaging of the phase output of a lock-in amplifier in mid-infrared photothermal vibrational microscopy is demonstrated for the first time in combination with nonlinear demodulation. In general, thermal blurring and heat transport phenomena contribute to the resolution and sensitivity of mid-infrared photothermal imaging. For heterogeneous samples with multiple absorbing features, if imaged in a spectral regime of comparable absorption with their embedding medium, it is demonstrated that differentiation with high contrast is achieved in complementary imaging of the phase signal obtained from a lock-in amplifier compared to standard imaging of the photothermal amplitude signal. Specifically, by investigating the relative contribution of the out-of-phase lock-in signal, information based on changes in the rate of heat transport can be extracted, and inhomogeneities in the thermal diffusion properties across the sample plane can be mapped with high sensitivity and sub-diffraction limited resolution. Under these imaging conditions, wavenumber regimes can be identified in which the thermal diffusion contributions are minimized and an enhancement of the spatial resolution beyond the diffraction limited spot size of the probe beam in the corresponding phase images is achieved. By combining relative diffusive phase imaging with nonlinear demodulation at the second harmonic, it is demonstrated that 1-μm-size melamine beads embedded in a thin layer of 4-octyl-4'-cyanobiphenyl (8CB) liquid crystal can be detected with a 1.3-μm spatial full-width at half-maximum (FWHM) resolution. Thus, imaging with a resolving power that exceeds the probe diffraction limited spot size by a factor of 2.5 is presented, which paves the route towards super-resolution, label-free imaging in the mid-infrared.