Search Results (134)

Phosphorus is an indispensable key element in life systems and materials science. Here in this work, several cyanoterphenyl-based phosphinic acid-bridged liquid crystal (LC) dimers of 2(CTOn)P (n = 6, 11) and their methyl esterification derivatives of 2(CTOn)P1E have been synthesized through hydrophosphination reaction followed by Suzuki coupling. The cyanoterphenyl LC dimers of 2(CTOn)P and methyl esterified 2(CTOn)P1E exhibit rich enantiotropic LC mesophases such as nematic (N), smectic A (SmA) and highly ordered smectic E (SmE), rather than the monotropic N or twist bend nematic (N_TB) displayed by the analogous phosphinic acid-bridged cyanobiphenyl LC dimers of 2(CBOn)P as reported previously. The phase transition temperatures of the cyanoterphenyl LC dimers 2(CTOn)P are also significantly higher than those of the cyanobiphenyl series, which is attributed to the larger π-conjugated system of cyanoterphenyl as compared with cyanobiphenyl, resulting in much enhanced π-π stacking interactions. However, the significantly enhanced interactions also make them extremely insoluble; thus, a different two-step synthesis pathway combining hydrophosphination with Suzuki coupling reactions was adopted. It is worth pointing out that by combining multiple characterization techniques, including DEPT 135°, ¹³C NMR, and HR-MS spectra, the definite molecular composition and structure of a byproduct with a third pro-mesogen attached via a branching alkyl spacer has been unambiguously demonstrated, which evidently deepens our understanding of the free radical-mediated hydrophosphination reaction mechanism, thereby providing valuable guidance for diminishing side reactions and achieving well-preparation of the high-purity phosphorus-containing LC dimers. Such phosphinic acid functionalized LC materials are envisioned to bear some unique application prospects. Full article

Photochromic molecules, capable of reversible isomerization under specific light irradiation, are pivotal for developing advanced photo-responsive materials. Azobenzene derivatives, in particular, are renowned for their significant conformational change, excellent reversibility, and high photostability. This study presents a novel cyclic diazo compound (CDTA) comprising two azobenzene units connected via flexible glycol chains. The photo-responsive behavior of CDTA doped into the liquid crystal 4-cyano-4′-octylbiphenyl (8CB) was systematically investigated. The composite exhibits a pronounced photo-induced phase transition from a liquid crystalline to an isotropic state under 365 nm UV irradiation, accompanied by a reversible change in light transmittance. The response kinetics were found to be highly dependent on temperature and dopant concentration. At 35 °C, the UV response time was accelerated to 6.8 s, attributed to the transition of the host 8CB from a smectic to a nematic phase. Furthermore, the composite demonstrated dual responsiveness: optical switching under UV light and electrical switching under an applied field in its nematic state. This work elucidates the interaction between molecular structure and photo-response in a liquid crystalline matrix, offering insights for designing next-generation smart windows and adaptive optical devices. Full article

We investigated the dynamics of molecular reorientation in freely suspended smectic liquid–crystal films (FSLCFs) under the influence of heat flux. We also examined how external thermal gradients affect molecular alignment in these ultra-thin films. FSLCFs were fabricated in a temperature-controlled chamber in this study. When heat flux was applied perpendicular to the film plane, rotation of line defects, known as 2π walls, was observed. This rotation resulted from thermomechanical torque acting on the molecular director, a phenomenon referred to as the Lehmann effect. By analyzing the changes in defect evolution, how heat flux drives the self-organization of liquid–crystal structures can be understood. In this study, we combined experimental observations and computational simulations to model and interpret the results. The results enhance the understanding of the underlying mechanisms governing molecular reorientation and defect dynamics in FSLCFs, particularly in non-equilibrium conditions, to study this mechanism in the microgravity environment. The results also contribute to the development of advanced liquid–crystal technologies, with potential applications in energy-efficient devices, adaptive materials, and space technology systems. Full article

We report an optical method to estimate local microviscosity in thermotropic liquid crystals using viscosity-responsive aggregation-induced emission luminogens. Pendant-type luminogens were designed by covalently attaching 4-cyano-4′-n-octyloxybiphenyl mesogens (n = 8, 10) to a bis(N,N-dialkylamino)anthracene emissive core. When introduced at 1.0 wt% into 8OCB and 10OCB, thermal and optical analyses showed that the intrinsic liquid crystal properties were essentially unchanged, indicating good structural compatibility. Temperature-dependent fluorescence and polarization measurements revealed that emission changes are governed mainly by microviscosity rather than macroscopic phase disruption. Effective microviscosity was evaluated from absolute fluorescence quantum yields using the Förster–Hoffmann relation. On this basis, the microviscosity in the nematic phase is 21 mPa·s for 8OCB upon cooling, which correlates with the enhancement in fluorescence. In the smectic phase, although the director distribution parameter remains nearly constant, the effective microviscosity is ca. 21 mPa·s for 10OCB and ca. 54 mPa·s for 8OCB, and the fluorescence varies smoothly with temperature, reflecting changes in local segmental mobility within the layered structure. These values are broadly consistent with reported viscosity ranges/trends for cyanobiphenyl-type liquid crystals. Full article

We present the design and characterization of a fully automated free-standing liquid crystal (FSLC) film holder, enabling remote and precise control of liquid crystal (LC) volume release, wiping speed, and temperature. Using 4-octyl-4′-cyanobiphenyl (8CB) as a test material, we systematically investigated the influence of formation parameters on the resulting film thickness and temporal evolution. Thickness measurements performed by monitoring the difference in optical path lengths of two arms of a standard optical intensity autocorrelation setup reveal that the wiping speed is the dominant factor determining both the initial film thickness and the subsequent annealing dynamics, while temperature becomes relevant only at the highest wiping speeds. Faster wiping speeds consistently produce thinner and more uniform FSLC films on the order of 3 µm, due to reduced LC mass deposition. Time-resolved optical and X-ray scattering measurements confirm the presence of an annealing phase following film formation, which can last for between 1 s and 10 min time scales, until a stable smectic configuration is reached. The holder provides a reliable and fully remote tool for generating high-quality FSLC films at rates up to 1 Hz, suitable for optical to hard X-ray experiments where direct access to the sample environment is limited. Full article

Bent-shaped liquid crystal (LC) dimers, trimers, and oligomers are intriguing because of their unique liquid crystallinities, which have gained further impetus after the identification of the twist-bend nematic (N_TB) phase in these molecules. LC trimers exhibiting the N_TB phase still remain relatively rare compared to the predominant LC dimers. We report the first homologs of selenium-linked LC trimers, 4,4′-bis[ω-(4-cyanobiphenyl-4′-ylseleno)alkoxy]biphenyls (CBSenOBOnSeCB) with carbon numbers in the alkyl-chain spacers, n = 7 or 9). Polarizing optical microscopy, differential scanning calorimetry, and X-ray diffraction (XRD) measurements were performed to investigate the phase transition behavior and mesophase structures of the trimers. Both CBSenOBOnSeCB trimers exhibited nematic (N) and N_TB phases. The XRD measurements revealed the presence of smectic A-like cybotactic clusters with a triply intercalated structure in the N and N_TB phases. The LC phase transition temperatures of CBSenOBOnSeCB were lower than those of the already-known ether-linked CBOnOBOnOCB and thioether-linked CBSnOBOnSCB counterparts. This trend is ascribed to the enhanced molecular bending and molecular flexibility of CBSenOBOnSeCB, which are caused by the smaller bond angle and greater bond flexibility of C–Se–C compared to C–O–C and C–S–C. This study offers a new molecular design for multiply linked LC oligomers with heavier chalcogen atoms. Full article

Photoluminescent liquid crystals with photoluminescence (PL) and liquid-crystalline (LC) properties have attracted attention as PL-switching materials owing to their thermally induced phase transitions, such as crystal → smectic A/nematic → isotropic phase transitions. Our group previously developed tetrafluorinated tolane mesogenic dimers linked by flexible alkylene-1,n-dioxy spacers, demonstrating that the position of the tetrafluorinated aromatic ring critically influences the LC behavior. However, these compounds exhibited very weak fluorescence owing to an insufficient D–π–A character of the π-conjugated mesogens, which facilitated internal conversion from emissive ππ* to non-emissive πσ* states. We designed and synthesized derivatives in which the mesogen–spacer linkage was modified from ether to ester, thereby enhancing the D–π–A character. Thermal and structural analyses revealed spacer-length parity effects: even-numbered spacers induced nematic phases, whereas odd-numbered spacers stabilized smectic A phases. Photophysical studies revealed multi-state PL across solution, crystal, and LC phases. Strong blue PL (Φ_PL = 0.39–0.48) was observed in solution, while crystals exhibited aggregation-induced emission enhancement (Φ_PL = 0.48–0.77) with spectral diversity. In LC states, Φ_PL values up to 0.36 were maintained, showing reversible intensity and spectral shifts with phase transitions. These findings establish design principles that correlate spacer parity, phase behavior, and PL properties, enabling potential applications in PL thermosensors and responsive optoelectronic devices. Full article

Among the recently developed ferroelectric nematic liquid crystals, FNLC-919, synthesized by Merck Electronics KGaA, stands out for its stable, room-temperature, ferroelectric nematic (N_F) phase. This renders it a promising candidate for both fundamental research and device-level applications. In this study, we present a comprehensive experimental investigation of FNLC-919, focusing on its structural, optical, dielectric, and elastic properties in the paraelectric nematic (N) and the intermediate antiferroelectric phase (dubbed N_X) that occur in a temperature range between the N and N_F phases. Key material parameters such as ferroelectric polarization, viscosity, and nanostructure are characterized as functions of temperature in all mesophases, while the orientational elastic constants are determined only in the N and N_X phases. Our findings are compared with prior results concerning the benchmark compound DIO that also exhibits the phase sequence N-N_X-N_F and reveals a smectic-like mass density wave coinciding with antiferroelectric ordering in the N_X phase. Full article

The functional integration of chiral liquid crystals and π-conjugated compounds has great potential for creating novel exotic materials. A series of chiral donor–acceptor (D–A)-type fluorenone derivatives was synthesized to investigate the influence of molecular structure upon their liquid-crystalline phase-transition behavior, ferroelectricity, photophysical properties, and photoconductive properties. Polarizing optical microscopy (POM), differential scanning calorimetry (DSC), and X-ray diffraction (XRD) analyses revealed that several D–A-type fluorenone derivatives exhibited liquid crystal (LC) phases. These chiral LC fluorenone derivatives exhibited polarization hysteresis in the chiral smectic C (SmC*) phase. Among the four fluorenone-based ferroelectric liquid crystals (FLCs), (R,R)-2a exhibited the largest spontaneous polarization (over 3.0 × 10² nC cm⁻²). The formation of intramolecular charge-transfer (ICT) states in each compound was evidenced by the UV–vis absorption spectroscopy. Ambipolar carrier transport in the SmC* phases of the fluorenone-based FLCs was elucidated by the time-of-flight (TOF) method. The mobilities of holes and electrons in the SmC* phases were on the order of 10⁻⁵ cm² V⁻¹ s⁻¹, which is on par with the carrier mobilities of low-ordered smectic phases in conventional LC semiconductors. Full article

Using reactive atomistic molecular dynamics, we simulate the network formation and bulk properties of chemically identical liquid crystal elastomers (LCEs) and isotropic elastomers. The nematic elastomer is from a family of materials that have been shown to be auxetic at a molecular level. The network orientational order parameters and glass transition temperatures measured from our simulations are in strong agreement with experimental data. We reproduce, in silico, the magnitude and onset of strain-induced nematic order in isotropic simulations. Application of uniaxial strain to nematic LCE simulations causes biaxial order to emerge, as has been seen experimentally for these auxetic LCEs. At strains of ~1.0, the director reorients to be parallel to the applied strain, again as seen experimentally. The simulations shed light on the strain-induced order at a molecular level and allow insight into the individual contributions of the side-groups and crosslinker. Further, the agreement between our simulations and experimental data opens new possibilities in the computational design of high-molecular-weight liquid crystals, especially where an understanding of the properties under mechanical actuation is desired. Moreover, the simulation methodology we describe will be applicable to other combinations of orientational and/or positional order (e.g., smectics, cubics). Full article

This study investigates the temperature-driven transmission switching behavior of our proposed smart glass, which utilizes a biphasic liquid crystal system under continuous application of a distinctive homeotropic (H) state voltage (V_H). By ascertaining V_H at temperatures near the phase transition point, the minimum voltage required to sustain the H state in the smectic A* (SmA*) phase is identified. Interestingly, this minimum V_H is unable to induce the H state in the chiral nematic (N*) phase, thereby maintaining a low-transmission scattering state; i.e., the focal conic (FC) state. This empowers passive, bidirectional optical switching between the transparent H state (in the SmA* phase) and the scattering FC state (in the N* phase) in an unaligned liquid crystal cell. This work employs two dissimilar chiral dopants, R811/S811 and CB7CB/R5011, both capable of inducing the SmA* phase. Neither resulting cell system underwent surface orientation treatment, and a black dye was incorporated to enhance the contrast ratio. The results indicate that the more efficacious CB7CB/R5011 system achieves a contrast ratio of 17 between the transparent and scattering states, with a corresponding haze level of 78%. To further reduce energy consumption, the experimental framework was transitioned from a continuous-voltage to a variable-voltage mode, giving rise to an increased haze level of 88%. The proposed switching scheme holds promise for diverse applications, notably in smart windows and light shutters. Full article

Soft nanocomposites were prepared by dispersing lipophilic carbon quantum dots (CQDs) in the liquid crystal compound 8CB. The quality of the dispersion was evaluated using fluorescence microscopy, while the microstructure of the samples was examined via polarized optical microscopy. We investigated the influence of CQDs on the orientational order parameter S as a function of temperature and sample composition by measuring birefringence. Additionally, the Fréedericksz transition threshold, along with the characteristic response and relaxation times, was measured for each sample as a function of temperature and applied voltage amplitude. The extracted rotational viscosity ${\gamma }_1$ exhibits a pretransitional divergence upon cooling toward the smectic-A phase. Its temperature dependence was analyzed using established models from the literature, and the corresponding activation energy was determined. Notably, our analysis suggests that the presence of CQDs alters the power-law dependence of ${\gamma }_1$ on the orientational order parameter S. The influence of CQDs on the elastic constants has been investigated. Full article

Three liquid crystalline mixtures were investigated, consisting of compounds abbreviated as MHPOBC and 3F5FPhF6 with molar ratios 0.9:0.1 (MIX5FF6-1), 0.75:0.25 (MIX5FF6-2), and 0.5:0.5 (MIX5FF6-3). The presence of the smectic A*, smectic C*, and smectic C_A* phases was observed in all mixtures. The hexatic smectic X_A* phase, present in pure MHPOBC, disappeared quickly with an increasing admixture of 3F5FPhF6. Vitrification of smectic C_A* was observed for the equimolar mixture, with the glass transition temperature and fragility index comparable to the pure glassforming 3F5FPhF6 component. Partial crystallization to conformationally or orientationally disordered crystal phases was observed on cooling in two mixtures with a smaller fraction of 3F5FPhF6. Broadband dielectric spectroscopy was applied to study the relaxation times in smectic and crystal phases. Vogel–Fulcher–Tammann, Mauro–Yue–Ellison–Gupta–Allan, and critical-like models were applied for analysis of the α-relaxation time in supercooled smectic X_A* and smectic C_A* phases. Full article

Fluorescent liquid crystals (LCs) have attracted considerable interest owing to their unique combination of fluidity, anisotropy, and intrinsic emission. However, most reported fluorescent LCs exhibit high phase transition temperatures and/or smectic phases, limiting their practical applications. To address this, we designed and synthesized a series of 2,1,3-benzothiadiazole (BTD)-based fluorescent nematic liquid crystals incorporating donor (D) or acceptor (A) groups to form D–A–D or D–A–A structures. Most of the synthesized derivatives exhibited supercooled nematic phases at room temperature. They composed various functional groups, such as secondary alkylamine, branched alkyl chain, and trifluoroacetyl groups, which are rarely used in calamitic nematic LCs. Notably, dimethylamine- and carbonyl-substituted derivatives exhibited relatively high fluorescence quantum yields (Φ_fl) in both solid and mesophase states, demonstrating their potential as efficient fluorescent materials. Our findings underscore the versatility of BTD-based mesogenic skeletons for designing room-temperature fluorescent nematic LCs with various functional groups. These materials offer promising opportunities for next-generation display technologies, optical sensors, and photonic applications. Full article

Interfaces between two fluids exhibit an excess free-energy cost per unit area that is manifested as surface tension. This equilibrium property generally depends on temperature, which enables the phenomenon of thermocapillary flow, wherein application of a temperature gradient having a component parallel to the surface generates a net in-plane effective body force on the fluid and thereby causes flow. Here, we study the thermocapillary flow in fluid smectic liquid crystal films freely suspended in air and stabilized in thickness by the smectic layering. If such films are a single layer (~3 nm) or a few layers thick, they have the largest surface to volume ratio of any fluid preparation, making them particularly interesting in the context of thermocapillary flow, which is two-dimensional (2D) in the film plane. Five-layer thick films in the form of spherical bubbles were subjected to a north–south temperature gradient field along a polar axis, with flow fields mapped using inclusions on the film surface as tracers, where the inclusions were “islands”, small circular stacks of extra layers. These experiments were carried out on the International Space Station to avoid interference from thermal convention of the air. The flow field as a function of latitude on the bubble can be successfully modeled using Navier–Stokes hydrodynamics, modified to include permeative flow out of the background fluid into the islands. Full article