The synthesis and phase behavior of two liquid crystalline racemates containing four aromatic rings, differing in the number of methylene groups, were reported. These materials form smectic phases, as was confirmed by dielectric spectroscopy. The mesomorphic properties of the studied racemates were compared with those of the appropriate (S) enantiomers previously synthesized. Since these materials are racemic mixtures, they were subjected to chiral separation by high-performance liquid chromatography. This research was conducted on two chiral columns based on polysaccharides. We identified optimal conditions that enable the baseline separation of these racemates, which can be scaled up for preparative purposes. Then, there is no need for repeated synthesis of chiral equivalents.

A series of 10 novel liquid crystalline compounds based on oligophenyl and tolane cores bearing laterally positioned cyano groups has been designed, synthesized, and systematically investigated. The molecular architecture was tailored by varying the number and position of lateral nitrile substituents, as well as the degree of core extension and terminal functionalization, in order to elucidate structure-property relationships governing mesomorphic, optical, and dielectric behavior. The majority of the compounds exhibit exclusively nematic phases, while no smectic ordering was observed, indicating that lateral cyano substitution effectively disrupts layered packing. The introduction of cyano groups significantly enables precise control over dielectric permittivity and induces negative dielectric anisotropy, with its magnitude and phase stability being directly governed by both the number and location of nitrile substituents. At the same time, extended π-conjugated cores provide relatively high birefringence (Δn ≈ 0.24), despite the presence of strong transverse dipoles, which typically reduce optical anisotropy. Comparative analysis reveals that excessive lateral polarity destabilizes the nematic phase and narrows its temperature range, highlighting the need for a balance between dipolar interactions and molecular anisotropy. The obtained results demonstrate that lateral cyano substitution constitutes an effective strategy for tuning negative dielectric anisotropy while retaining favorable optical properties. Overall, these results identify lateral cyano substitution as a useful molecular-design strategy for developing high-birefringence nematic materials with negative dielectric anisotropy, which may serve as building blocks for future microwave/GHz-oriented liquid-crystalline mixtures.

A set of new liquid-crystalline compounds featuring a thieno[3,2-b]thiophene core was prepared to study how molecular structure influences both optical and dielectric characteristics. Determination of the mesomorphic properties of the synthesized compounds, along with the investigation of their optical and dielectric characteristics, allows for their characterization and classification as components of mixtures intended for microwave applications. The design of the structures was based on the functionalization of the heterocyclic thieno[3,2-b]thiophene core, which serves as the central core unit. They constitute a complement and a point of comparison with the previously presented structures exhibiting high birefringence and containing the thienothiophene ring. Optimization of the reaction conditions along the synthetic pathway to the final compounds allowed for diversification of the structures in terms of the type of terminal substituent, degree of fluorination, nature of the linking groups, and the length of the mesogenic core. The characterization of the obtained mesogens, explicitly designed for microwave applications, limited by the temperature range over which liquid crystalline properties are exhibited, indicates that the chosen research area represents a promising direction for the use of these materials as electrically controllable dielectric media for microwave applications.

A series of novel liquid-crystalline compounds based on a thieno[3,2-b]thiophene core was synthesised to investigate the relationship between molecular structure and optical as well as dielectric properties. Structural modifications involved variations in terminal polar groups (isothiocyanate or cyano), lateral halogen substituents, ethynyl linkers, and terminal thioalkyl chains. Thermal analysis revealed stable nematic phases for most compounds, with some derivatives exhibiting smectic A phases over broad temperature ranges. Optical studies demonstrated high birefringence values exceeding 0.36 for selected materials, primarily attributed to enhanced molecular polarizability anisotropy introduced by the conjugated core and polar substituents. Incorporation of ethynyl linkers and isothiocyanate terminal groups effectively increased transition temperatures and modified mesophase stability. The results confirm that precise molecular design involving heteroaromatic cores and sulfur-containing chains enables tuning of both mesophase behavior and optical anisotropy, offering strategies for the development of high-performance photonic materials.

Non-chiral liquid crystals (LCs) exhibiting ferroelectricity, distinguished by their dynamic responsiveness to external stimuli and high spontaneous polarization, provide renewed impetus for research into this area of soft matter and open novel application possibilities. Consequently, identifying structural elements within LC compounds that promote ferroelectricity in non-chiral systems is of critical importance. In this work, two homologs of rod-like compounds, with phenyl and ester groups in the rigid core substituted by fluorine atoms, differing by a single methylene unit, were synthesized and comprehensively analyzed using complementary experimental techniques and quantum-mechanical modeling. This systematic study presents the first documented instance in which such a minimal structural modification markedly influences the polarity of smectic phases in two homologs, without substantially altering phase transition temperatures, particularly the sequence and temperature ranges of smectic and nematic phases. Additionally, findings reveal that the longer homolog, which exhibits paraelectric phases, demonstrates a pronounced capacity to maintain ferroelectric phases in mixtures. These results provide new insights into the critical structure-property relationships between molecular architecture and ferroelectric characteristics in LCs, facilitating the targeted design of non-chiral compounds with polar phases. Moreover, the properties of the studied mixtures underscore the potential to develop multicomponent LC mixtures with stable ferroelectric properties in a broad temperature range, a feature of considerable significance for practical applications.

We have designed new chiral smectic mesogens with the -CH2O group near the chiral center. We synthesized two unique rod-like compounds. We determined the mesomorphic properties of these mesogens and confirmed the phase identification using dielectric spectroscopy. Depending on the length of the oligomethylene spacer (i.e., the number of methylene groups) in the achiral part of the molecules, the studied materials show different phase sequences. Moreover, the temperature ranges of the observed smectic phases are different. It can be seen that as the length of the alkyl chain increases, the liquid crystalline material shows more mesophases. Additionally, its clearing (isotropization) temperature increases. The studied compounds are compared with the structurally similar smectogens previously synthesized. The helical pitch measurements were performed using the selective reflection method. These materials can be useful and effective as chiral components and dopants in smectic mixtures targeted for optoelectronics and photonics.

The dielectric properties of synclinic (ferroelectric SmC*) and anticlinic (antiferroelectric SmCA*) smectic liquid crystals composed of molecules of one chiral version (S) are presented and compared with properties of racemic mixture (R, S), showing SmC and SmCA phases. The racemic mixture completely loses its ferroelectric and antiferroelectric properties. Surprisingly, only one dielectric mode observed in the antiferroelectric SmCA* phase disappeared in the dielectric response of the racemic SmCA phase. Additionally, we observed that in the SmC phase, seen in the racemic mixture, the weak dielectric mode (named the X mode) is detected, which seems to be the continuation of the PL mode existing in the racemic SmCA. Moreover, this mode in the racemic SmC has nothing to do with the Goldstone mode, typical for the SmC* phase. This paper describes in detail the real and imaginary parts of dielectric permittivity in smectic phases for the enantiomer and racemate with and without a DC field, compares the properties of the X and PL modes, and discusses the full scheme of dielectric modes in enantiomer and racemate.

The oblique helicoidal structure is formed in right-angle cholesterics under the applied electric field. The electric field changes the pitch and cone angle but preserves the single-harmonic modulation of the refractive index. As a result, in such a supramolecular system, we can tune the selective reflection of light in a broad range. Here, we report that structural colors can be tuned by simultaneously illuminating the structure with UV light and the action of an electric field. The cholesterics with the oblique helicoidal structure were doped with newly designed rod-like, chiral, and bent-shaped azo-photosensitive materials characterized by a very low rate of thermal back cis (Z) – trans (E) isomerization. The E-Z isomerization of the photo-active compounds under UV light causes the red shift of the selective light reflection in the cholesteric mixtures. We found that the molecular structure of the photosensitive materials used affects the reflection coefficient, bandwidth, response time to UV irradiation, and tuning range. The effect was explained by considering the effect of molecular matching, cis–trans isomerization, and electric field action. We investigated the dynamics of molecular changes in the oblique helicoidal structure under the influence of external factors. The designed supramolecular system has the potential application in soft matter UV detectors.

The growing demand for enhanced optical quality and faster electro-optical response in liquid crystal (LC) photonic devices has expanded the search for advanced materials capable of improving the properties of LCs beyond conventional ones. Among these compounds are LC dimers with ferroelectric and antiferroelectric properties which can be incorporated into LC mixtures to enhance performance. However, existing dimers often feature high melting temperatures, enthalpies, and other physicochemical characteristics that render them unsuitable as dopants in antiferroelectric liquid crystal (AFLC) mixtures targeted to modern photonic devices. Here, we show the design and physicochemical properties of novel dimers which are characterized by low melting points, high tilt angles and spontaneous polarizations, temperature-stable helical structures, and reasonably broad temperature ranges of ferroelectric or antiferroelectric phases. These features have facilitated the effective use of one dimer as a dopant in AFLCs. This eliminates the primary drawback of the electro-optical effect based on the surface-stabilised geometry of AFLCs by strongly promoting the anticlinic state in this effect. Importantly, for the first time, the above can be achieved without affecting any other physicochemical or optical properties of AFLCs. Thus, the obtained results represent a pivotal link between the longstanding concept of developing AFLCs that meet the stringent requirements for electro-optical effects based on surface-stabilised geometry and the realization of novel photonic devices demonstrating all the benefits of this effect.

The recent discovery of a new ferroelectric nematic (NF) liquid crystalline phase became of utmost interest for the liquid crystal (LC) and the whole soft and condensed matter fields. Contrary to the previously known ferroelectric LC materials, whose ferroelectric characteristics were much weaker, new polar nematics exhibit properties comparable to solid ferroelectrics. This discovery brought about tremendous efforts to further explore compounds showing these phases, and fascinating physical properties have been reported. Herein, we present the first synthesized compounds with the enantiotropic ferro- (NF) and antiferroelectric (NX) nematic phases. The enantiotropic nature and an unprecedentedly broad temperature range of NF and NX phases are confirmed by various experimental techniques: polarized-light optical microscopy (POM) observations, different scanning calorimetry (DSC), dielectric spectroscopy, second harmonic generation (SHG), and molecular modeling. The presented achievements in designing achiral compounds that exhibit enantiotropic polar nematic phases with ferro- and antiferroelectric properties significantly contribute to the development of multicomponent mixtures with a broad temperature range of NF and NX phases down to room temperature. Furthermore, this accomplishment considerably enhances the general understanding of the structural correlations that promote polar nematic liquid crystal phases with high thermodynamic stability. Finally, this work may benefit various applications in photonic devices.

Antiferroelectricity is a desirable property of liquid crystalline materials. Therefore, we synthesised and studied two new chiral rod-like mesogens with a molecular core based on two biphenyls connected via ester linkage, with the phenyl substituted by a fluorine atom. The studied mesogens are characterised by nuclear magnetic resonance spectroscopy and mass spectrometry analysis. They have methyl heptyl in the chiral chain and exhibit an antiferroelectric phase in a very broad temperature range. We investigated their mesomorphic properties and confirmed the phase identification by differential scanning calorimetry and broad-frequency dielectric spectroscopy measurements. Additionally, we compared the studied mesogens with previously synthesised analogous materials. Two mixtures were formulated using a base mixture and new mesogens. The helical pitch of the synthesised mesogens and formulated mixtures was estimated using the selective reflection method. [GRAPHICS]

We investigated the electrical properties of the liquid crystal compound 4-(4-nitrophenoxycarbonyl)phenyl 2,4-dimethoxybenzoate, known as RM734, exhibiting a ferroelectric nematic phase. The influence of alternating (AC) and direct (DC) current electric fields on the switching process of the polarization vector and dielectric constant of planarly aligned ferronematic and nematic phases were examined. The decrease of the real part of electric permittivity in the ferronematic phase and the creation of a ferroelectric order in the nematic phase under a DC field were demonstrated. The analysis of the results reveals the latching of the ferroelectric state. The applied DC field created a ferroelectric mode in the nematic phase. A new model of collective and molecular relaxations considering the domain structure of the ferronematic phase was proposed. The temperature and DC field dependence of dielectric properties was shown. Spontaneous polarization was measured using the field reversal technique. The spontaneous polarization value reaches the maximum at a fixed temperature.

The solid dielectrics used in the capacitors exhibit rather high-frequency relaxations. This means that in the radio-frequency range, the capacitors exhibit a constant capacity. When liquid crystal is put into the capacitors, it is observed that in the radio-frequency range the capacity changes (decreases with frequency). This is due to the fact that liquid crystals exhibit relaxation in the radio-frequency range. In this paper, the formulas for the electric response of a low-frequency RC filter with liquid crystal characterized by complex electric permittivity are derived. One Debye-type relaxation is assumed in the calculations. The influence of strengths and relaxation time (frequency) of relaxation mode in liquid crystal on the electric response of low-frequency filters is discussed.

Abstract This work presents the application of an experimental nematic liquid crystal (LC) mixture (1929) in a large aperture lens. The LC material is composed of terphenyl and biphenyl derivatives compounds with an isothiocyanate terminal group and fluorinated lateral substituents. The substitution with a strongly polar isothiocyanate group and an aromatic rigid core provides $$\pi$$ π -electron coupling, providing high birefringence ( $$\Delta n = 0.3375$$ Δ n = 0.3375 at 636 nm and 23 °C) and low viscosity ( $$\eta$$ η = 17.03 mPa s). In addition, it also shows high values of birefringence at near infrared (0.318 at 1550 nm). The synthesis process is simple when comparing materials with high melting temperatures. The excellent properties of this LC mixture are demonstrated in a large aperture LC-tunable lens based on a transmission electrode structure. Thanks to the particular characteristics of this mixture, the optical power is high. The high birefringence makes this LC of specific interest for lenses and optical phase modulators and devices, both in the visible and infrared regions.

Dielectric (impedance) spectroscopy of liquid crystals is a powerful experimental technique. It is especially essential because liquid crystals in many applications are still controlled by the electric field. In this paper, the problems with the high frequency (>1 MHz) measurements in classical (in the shape of the flat capacitor) measuring cells are discussed. The procedure for overcoming measurement difficulties was presented and applied to the dielectric response of antiferroelectric, binary mixture. Additionally, the paper presents the first example of extending the measuring range of dielectric spectroscopy from 1 MHz to ~50 MHz by overcoming the parasitic effect related to resonance in measuring setup.

Four new liquid crystalline three ring enantiomers in the (S) configuration were designed, synthesised and investigated. The structure of the compounds was confirmed by proton and carbon nuclear magnetic resonance. Properties of the materials were characterised by the polarising optical microscopy, differential scanning calorimetry, electro-optical measurements and dielectric spectroscopy. The helical pitch was measured by a spectrophotometry method. Two materials possess a ferroelectric SmC* phase in a broad temperature range. The next two materials exhibit an antiferroelectric SmCA* phase as well as the ferroelectric SmC* phase. The new (S) enantiomers were used to formulate multicomponent eutectic mixtures with appropriate properties in Surface Stabilized geometry.

Ion-doped fluorinated smectics are good candidates for use in the dynamic light scattering effect where electro-optical properties of a liquid crystal cell are controlled by changing the frequency of an electric field. In this work, we demonstrate the electrical properties of a liquid crystal mixture exhibiting a monolayer SmA phase. The paper presents a discussion on the influence of the ionic dopant on relaxation processes and electrical conductivity. The temperature measurements of the liquid crystal mixture of positive dielectric anisotropy were conducted in planarly and homeotropically aligned cells from the isotropic phase to the nematic and smectic A phase. The observed ionic relaxation is discussed, and its parameters were calculated and analyzed. The investigated material can be used in smart windows and liquid crystal displays with the memory effect.

ABSTRACT The homologous series of the new antiferroelectric liquid crystals, containing 2ʹ,3ʹ-difluorosubstituted terphenyl as the mesogenic core have been synthesised and evaluated. The synthetic routes with their mesomorphic properties were described. Also other physical properties are delivered. The liquid crystal phases were preliminarily determined by thermomicroscopic and microcalorimetric measurements and verified by dielectric measurements and miscibility methods. The temperatures and enthalpies of the phase transitions are given. Graphic abstract

This paper presents the dielectric properties of the isotropic liquid and nematic phase at the phase transition. One strong molecular relaxation is observed in both phases. It is interpreted as related to the relaxation around a short molecular axis, due to the fact that molecules possess a strong longitudinal dipole moment. In the isotropic liquid the relaxation is described by the Debye model, while after entering the nematic phase (at cooling) relaxation becomes described by the Cole-Cole model. The distribution parameter of the Cole-Cole model changes from 0.05 (10 degrees above the temperature of the Iso-N transition) to 0.09 (exactly at the phase transition Iso-N), and finally, it reaches 0.35 (10 degrees below the Iso-N transition). Additionally, we observe that ion contribution to the dielectric response is not influenced by the phase transition. All relaxation parameters are discussed within the context of the phase transition phenomena.

Novel chiral three-ring compounds with the -CH2O group close to chirality centre were synthesised and their properties were studied. The phase transitions and phase sequences were observed using a polarising optical microscope. The phase transition temperatures and enthalpies were checked by differential scanning calorimetry. A broad-frequency dielectric spectroscopy was also used to confirm the phase transition temperatures as well as the phase sequence. The helical pitch was measured by the spectrophotometry method. It was found that the compounds differing only in one lateral substituted fluorine atom create two different chiral tilted smectic phases, one a ferroelectric phase (SmC*) and the other an antiferroelectric phase (SmCA*). [GRAPHICS] .