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Several new liquid crystalline chiral ester enantiomers in the (S) and (R) configuration were designed and characterised. In order to tune their mesomorphic properties, the molecular core was laterally substituted by fluorine atoms in different positions on the benzene ring placed in the molecular core far from the chiral centre. All the materials possess the self-assembling behaviour, specifically the paraelectric orthogonal smectic A*, the ferroelectric tilted smectic C* and antiferroelectric tilted smectic CA* phases over a broad temperature range down to room temperature. Properties of the materials were characterised by the polarising optical microscopy, differential scanning calorimetry, electro-optics and dielectric spectroscopy. Due to high chemical stability, reasonably broad temperature ranges of polar smectic mesophases (up to 110 °C) and very high values of the optical tilt angle (40–45°) at saturation, these materials can be used as chiral dopants for the multicomponent orthoconic mixture design aimed for development of advanced electro-optic and photonic devices.

4′-Alkyl-4-alkoxy-3-fluorobiphenyls and laterally mono-, two- and three-fluorosubstituted 4″-alkyl-4-fluoroterphenyls were synthesized and used as the components of mixtures with a broad temperature range of the monolayer smectic A phase and the Cr-SmA1-Iso or Cr-SmA1-N-Iso phase sequence. Several ionic potassium complexes of 18-crown-6-ether and dibenzo-18-crown-6-ether with different anions (Br−, ClO4−, 4-octylphenolate, 3,4-difluorophenolate, 3,5-difluoro-4-cyanophenolate and 4-dodecylbenzenesulfonate) were prepared and their solubility and conductivity in fluorobenzene were measured. Properties of dynamic scattering and clear states (threshold and saturation voltages) of two types of mixtures (mixture A with Cr-SmA1-Iso and mixture B with Cr-SmA1-N-Iso phase sequences) doped with above mentioned ionic compounds have been tested. The mixture B has the smectic layers more defected and it shows excellent properties to design displays with memory or smart windows.

Orthoconic Antiferroelectric Liquid Crystals (OAFLC) are recognised as a promising medium for display and photonic applications due to their unique electrooptical properties. The application of OAF...

Three newly prepared binary mixtures exhibiting chiral tilted smectic phases have been studied using differential scanning calorimetry, dielectric spectroscopy and electro-optic method, as well as X-ray diffraction. Broad temperature range of ferroelectric and antiferroelectric phases was detected in these mixtures and temperature dependence of spontaneous polarization, tilt angle and switching time were measured for all of them. It's occurred that all of the studied mixtures are orthoconic antiferroelectric liquid crystals. Based on the X-ray diffraction results, the temperature dependence of layer thickness in the paraelectric, ferroelectric and antiferroelectric phases was found. By using dielectric spectroscopy, Goldstone mode was identified in the ferroelectric phase, while antiphase fluctuations of azimuthal angle have been found in the antiferroelectric phase. Based on the results of the complementary methods, the transition temperatures were found as well as the order of the para-ferroelectric phase transition was determined as non-continuous one with critical parameter $\beta$ equal to ca. 0.25.

The infrared spectra were registered for series of three-ring liquid crystalline esters, differing in the structure of alkyl chain, in the substitution of benzene ring by fluorine atoms and in the type of helicoidal structure in the chiral smectic CA phase with antiferroelectric properties. The influence of molecular structure on the shift of signals coming from carbonyl group, located in the rigid core, was observed. Keywords: liquid crystals, helicoidal structure, chiral smectic CA phase, antiferroelectric crystalline phase, infrared spectroscopy

Three-ring chiral liquid crystalline compounds, forming antiferroelectric phase, differing in the structure of alkyl chain and in the substitution of benzene ring by fluorine atoms were studied. The measurements of helical pitch, based on the selective light reflection phenomenon, were performed as well as 1H and 13C NMR spectra at room temperature were registered. The influence of molecular structure as well as the type of helicoidal structure on the chemical shift of signals coming from chiral center was observed. Keywords: liquid crystals, helicoidal structure, nuclear magnetic resonance, antiferroelectric phase

A broad-frequency dielectric spectroscopy (100 Hz to 10 MHz) was used to investigate newly synthesized fluorinated compound. This compound exhibits a wide-temperature ferroelectric phase. Due to the fact that the compound does not crystallize at temperatures available in our DSC equipment, additional measurements were done at the very low temperatures (down to −100 °C) to find the crystallization temperature. Finally, we did not manage to crystallize the investigated compound. Compound under studies seems to be overcooled. Observed dielectric modes are described and their parameters are shown in this paper. Additionally, DC field influence on dielectric response is shown and analyzed here. Both modes observed at the low temperature are recognized as the molecular ones.

Five new bicomponent eutectic mixtures based on compounds different in the bridge between a rigid core and a chiral centre (-COO- or -CH2O-) or in the optical purity (‘S’ or racemic ‘R,S’) were prepared and characterised. Their mesomorphic properties were tested by means of polarising optical microscopy and differential scanning calorimetry. The helical pitch of prepared mixtures was estimated with selective reflection method. The optical tilt angle Θ of mixtures was also measured and discussed.

Four new synthesised liquid crystalline compounds belonging to the homologous series of fluorinated biphenyl benzoate esters have been studied to compare their dielectric and electrooptic properties. Three of the studied compounds exhibited ferro- and antiferroelectric phases while one of them exhibited only one liquid crystalline phase – ferroelectric SmC*. No paraelectric phase was detected and straight transition between isotropic liquid and ferroelectric phases was observed for all studied compounds. Tilt angle for all of the studied compounds was equal to ca. 45ᵒ in the liquid crystalline phases, except temperature range close to the isotropic liquid–ferroelectric smectic phase transition. Temperature dependences of helical pitch, spontaneous polarisation and switching time have been determined. Based on XRD results, temperature dependence of the layer thickness has also been found. Only one relaxation process has been revealed in the ferroelectric as well as antiferroelectric phases, even the bias field up to 8 V/µm was applied. The dielectric and electrooptic data are discussed based on the mean-field theory predictions.

New compounds (S)-4ʹ-(1-methylheptyloxycarbonyl)biphenyl-4-yl 4-[3-(2,2,3,3,4,4,5,5,5-nonafluoropentyloxy)prop-1-oxy]benzoates were synthesised and characterised. Their mesomorphic properties were tested by means of polarising optical microscopy and differential scanning calorimetry. The multicomponent antiferroelectric high tilt mixture with long pitch has been also formulated and characterised. The helical pitch of prepared mixture was estimated with selective reflection method.

New orthoconic antiferroelectric liquid crystalline materials were synthesised and characterised in their racemic forms and as (S) enantiomers. The materials possess oligo-methylene spacers of different lengths in semi-fluorinated achiral chains and lateral substitution by fluorine at two different positions of the molecular core. For comparison purposes, analogical materials without fluorine lateral substitutions were also prepared. Polysaccharide chiral stationary phases based on two different chiral selectors were used for the separation of the enantiomers of the individual racemic mixtures by high-performance liquid chromatography. A baseline separation of (S) and (R) enantiomers was obtained for four of the six studied liquid crystalline materials. Two of the materials were partially separated under the optimised separation conditions. The elution order of the individual enantiomers in the racemic mixtures was successfully assigned, as pure (S) enantiomers of all the studied materials were av...

A homologous series of chiral three ring esters were synthesised and their properties were studied. The materials possess an antiferroelectric phase (SmCA*) or/and a ferroelectric phase (SmC*), which was confirmed by observations of microscopic textures using a polarising optical microscope. The phase transition temperatures and enthalpies were checked by differential scanning calorimetry. The helical pitch was measured by a spectrophotometry method. For all cases the helix is right-handed, in the antiferroelectric phase the helical pitch increases with temperature, and in the ferroelectric phase the helical pitch is short.

Physical properties and the phase sequence of (S)-4′-(1-methylheptyloxycarbonyl)biphenyl-4-yl 4-[7-(2,2,3,3,4,4,4-heptafluorobutoxy) heptyl-1-oxy]-2-fluorobenzoate exhibiting the liquid crystalline...

Two new binary liquid crystalline mixtures composed from the chiral liquid crystalline materials with partially fluorinated non-chiral chain and without lateral substitution at the molecular core h...

Chiral liquid crystals with three-ring rigid core were examined. The method based on the selectively reflected light was used to determine the helical pitch. The helical twist sense was worked out using the polarimetry method. 1H and 13C NMR measurements were performed. The influence of three molecular structure parameters: the type of chiral centre, the length of non-chiral chain and substitution of benzene ring by fluorine atoms, on helical pitch, handedness of helical structure and values of chemical shift in proton and carbon spectra was determined. The change of the length of non-chiral terminal chain has the most significant influence on the temperature dependence of helical pitch. All tested parameters have the biggest influence on the values of chemical shift of atoms in the chiral centre.

The electro-optical properties of orthoconic antiferroelectric liquid crystals of some analogues of (S)‑MHPOBC ((S)‑4‑(1‑methylheptyloxy)carbonylphenyl 4'-octyloxy-4-biphenylcarboxylate) have been investigated and discussed in terms of the structure property correlations of liquid crystalline molecules. Polarisation field reversal technique has been used for their characterisation. In this study the occurrence of such a high value of spontaneous polarisation (Ps) for the investigated compound is especially noteworthy as they comprise a bulky chiral unit, zigzag ester linkage and polar fluorinated terminal. Lengthening of oligomethylene spacer in the terminal chain and placement of fluorine atom in the molecular core structure leads to reduction in the value of Ps. The Ps data suggest that the nature of the chiral smectic C (SmC*) to smectic A (SmA) phase transition is of second order and the critical exponent β is in the range 0.19–0.34. The ‘V-shaped’ mode or thresholdless switching in such high-polarisa...

A broad temperature antiferroelectric binary mixture has been investigated by means of dielectric spectroscopy. The sample was cooled down to –70°C. It was found that the sample was still in antiferroelectric phase. This is the widest antiferroelectric mixture ever seen (∼170°) in which three well-separated modes have been detected at room temperature. In addition, the bias field influence on existing modes has been observed. All modes change their strengths with bias field. Results show that the fastest mode, called X mode previously, gradually disappears around –30°C. When the temperature decreases below –40°C, one can indisputably observe additional mode, faster than X mode. This mode (named as Y mode) observed for extra low temperatures is bias independent. It can be the molecular mode, connected with rotation around long molecular axis. The rotation around short molecular axis seems to be blocked in antiferroelectric packing. To calculate parameters of observed modes, Cole–Cole model was used. The pa...

Several new binary liquid crystalline mixtures have been designed and their properties were studied by complementary methods. It has been shown that even both pure components used for the mixture design possess the ferroelectric behaviour; the induced antiferroelectric smectic phase has been detected for one of the prepared mixtures. The phase diagram has been constructed and the existence of the antiferroelectric phase was confirmed by switching time and dielectric spectroscopy measurements. Some of the resulted mixtures possess very high values of the tilt angle that reaches close below 45° degrees at saturation. Values of spontaneous polarisation were found within 50–200 nC/cm2 in dependence of the mixture’s composition. Due to specific properties, the obtained mixtures might be interesting for further design of multicomponent mixtures and formulation of the advanced nanocomposite systems.

Antiferroelectric Sm phase can be created at cooling from Iso, SmA* and SmC* phases. When antiferroelectric phase appears from the ferroelectric one, the magnitude of Goldstone mode detected in SmC* is much higher than the amplitude of low frequency PL mode observed in Sm . Due to this fact it is impossible to compare both modes. Such a comparison would be interesting because the mechanism of forming the Goldstone and PL modes seems to be similar. In this article we compare the Goldstone mode with the PL one. It is possible because the new racemic mixture, which shows both SmC* and Sm phases, was prepared. Moreover, the magnitude of the Goldstone mode in the racemate is comparable with the magnitude of PL mode, which makes the comparison possible. The results show that the behavior of PL and Goldstone modes are very similar. The parameters of the Goldstone mode in SmC* and parameters of PL mode in Sm change continuously.

A bicomponent mixture in the orthoconic aniferroelectric phase, based on three-ring esters with fluorine atoms and ether group in a nonchiral chain, was doped with a variety of cyano-terminated compounds containing different numbers of phenyl rings in a rigid core and a terminal chain of different chirality. Compounds with two chiral chains were added to the basic mixture. The influence of the structure and concentration of dopant on the temperature-dependence of helical parameters, such as helical pitch and twist sense, were assessed by spectrophotometric and polarimetric methods. Long cyano-terminated compounds were found to be better than the other dopants tested for improving the usable properties of the antiferroelectric mixtures.

The attempt of the engineering of modern liquid crystalline orhoconic antiferroelectric smectic material OAFLC with remarkable optical properties is reported. The high tilted anticlinic antiferroelectric parent mixtures were formulated and studied. Subsequently those parent mixtures were doped with homo- and heterostructural dopants with selected properties including a molecular shape, molecular dipole moment μ value and orientation and molecular conformation. The effects of the doping are described. The doping affecting a single phase parameter is reported. Examples of functional dopants are presented and their influence on the physical and structural properties of doped mixture is shown.

In a large class of smectic mixtures prepared at our University, the phase transition between chiral ferroelectric smectic C (SmC*) and chiral antiferroelectric smectic C (SmCA*) phases can be observed on cooling. Under bias field the temperature of the phase transition SmC*−SmCA* decreases (ca. 100°C in the investigated mixture). The transition is called: unwound SmC*−twisted SmCA* phase transition. The Goldstone mode in SmC* phase is reduced by a direct current field while two modes (PH and PL) in the SmCA* phase are amplified. The amplitude of the fast X mode observed in the SmCA* phase is reduced. The aim of this paper is to show how parameters of the modes in SmCA* phase (calculated from Cole–Cole model) change with bias voltage—when twisted structure in SmCA* phase is gradually unwound. The character of the modes observed in SmCA* is discussed. A new effect is shown: a high value of dielectric loss is detected in the unwound SmC* phase, which is very close to SmCA*.

The temperature dependence of helical pitch for members of an homologous series of orthoconic antiferroelectric compounds (3FmHPhF) and their bicomponent mixtures (m = 3 and 5 as well as m = 3 and 7) has been measured by the method of selective light reflection. The compounds have the same chiral centre but they have different temperature dependence of the helical pitch as well as the helical twisting sense in SmC*A phase: right for member m = 3, left for m = 7, and both right and left for m = 5. For this last homologue, the change of twisting sense is connected with the appearance of the unwound structure. Concentration dependence on helical pitch was investigated in the mixtures. It was demonstrated that it is possible to obtain mixtures with desirable high pitch and also with totally unwound structure.

The synthesis and properties of a few dozen highly evolved analogues of (S)-MHPOBC are reported. The liquid crystal phases, and phase transition temperatures and enthalpies, as evidenced by polarized optical microscopy and differential scanning calorimetry, respectively, are given. The helical pitch in pure compounds and some mixtures is estimated using the selective reflection method. All of the compounds show antiferroelectric phases, and some key structure–property relationships for the new materials are reported. Specifically, it is found that the length of the oligomethylene segment of a novel partially fluorinated alkoxy ether tail incorporated into the structures strongly influences the stability of the antiferroelectric phase and the observed phase sequences, as well as the values of the helical pitch and its temperature dependence. The formulation of a family of broad temperature range eutectic mixtures possessing the highly desirable orthoconic antiferroelectric phases with long helical pitch is described.

Four racemic compounds (R, S)-4′-(1-methylheptyloxycarbonyl)biphenyl-4-yl 4-[3-(2,2,3,3,4,4,4-heptafluorobutoxy)prop-1-oxy]benzoates were synthesized and characterized. Their mesomorphic properties, such as phase transitions temperatures and enthalpies were measured by polarizing optical microscope and differential scanning calorimetry. The example of mixture containing racemic components and its properties is presented.

New antiferroelectric fluorinated mixture W-1000 was made. Typical two dielectric modes with frequencies around 1–10 kHz and 100 kHz–1 MHz were detected in . Additionally high frequency mode was observed with relaxation frequency higher than 1 MHz. All modes in antiferroelectric phase were discussed.

Orthoconic Antiferroelectric Liq. Cryst. (OAFLC) have been extensively studied due to their unique electrooptical properties [1,2]. Practical implementation of this kind of liquid crystalline medium experiences many obstacles including a number of parasitic effects deteriorating the electrooptical performance. In search for working OAFLC a mixture with the helical pitch longer than the typical cell gap was formulated. Using this mixture near perfect optical uniformity and excellent dark state at the zero electric field applied was obtained. The physical and structural properties of mixture are presented and their parameters are discussed. The electrooptical performance is presented and discussed.

In this work, the physical properties of newly synthesized liquid crystalline compound exhibiting two liquid crystalline phases (ferroelectric and antiferroelectric) were studied. Based on the results of differential scanning calorimetry, polarizing microscopy, and photoelastic modulator methods, the temperature dependences of spontaneous polarization, tilt angle, switching time, and birefringence in the ferroelectric, as well as antiferroelectric phases were determined. Furthermore, the influence of the external electric field on the liquid crystalline textures was studied and the phase sequences at heating and cooling were revealed. The temperature dependence of spontaneous polarization was analysed by means of Landau mean-field theory, and the critical parameter β obtained for ferroelectric liquid crystalline and isotropic liquid transition was 0.21 which is close to 0.25, the value characteristic for tri-critical point.

Two methods of synthesis of chosen 1-[4-(1-methyl-heptyloxycarbonyl)phenyl]-2-[4′-(2,2,3,3,4,4,4-heptafluorobutoxy-alkoxy)biphenyl-4-yl]ethanesand 1-[3-fluoro-4-(1-methylheptyloxy-carbonyl)phenyl]-2-[4′-(2,2,3,3,4,4,4-heptafluorobutoxyalkoxy)bi-phenyl-4-yl]ethaneshave been proposed, checked and compared. The compounds were preparedby Sonogashira coupling of 4-benzyl-oxy-4′-ethynylbiphenylwith appropriate 4-halobenzoate esters followed by parallel hydrogenationof ethynylene bridge and debenzylation of hydroxyl group. The 1-[4-(1-methylheptyloxycarbonyl)phenyl]-2-[4′-hydroxybiphenyl-4-yl]ethaneand 1-[3-fluoro-4-(methoxycarbonyl)phenyl]-2-[4′-hydroxybiphenyl-4-yl]ethane thusobtained has been transformed into final products by Mitsunobu reactionwith ω-(2,2,3,3,4,4,4-heptafluorobutoxy)alkan-1-ols, followedby the replacing of an ester terminal chain in the case of secondmethod.

Influence of the electric field upon alignment of molecules in ferro- and antiferroelectric phases has been studied for two fluoro-substituted compounds exhibiting antiferroelectric phase at room temperature. Two different relaxation processes have been revealed in the ferroelectric as well as antiferroelectric phase. Low temperature value of spontaneous polarization is ca. 130 nC/cm2 for both substances studied. The substances align very well in the external electric field — a mono-domain of the ferroelectric SmC* phase can be obtained in about 3.5 hours.

Electrooptical properties of several new orthoconic antiferroelectric liquid crystal mixtures with partially fluorinated alkoxyalkoxy terminal chains have been investigated in order to select the best mixture for display applications. Electrooptical studies have been performed on these orthoconic materials aiming at evaluating their static and dynamic performance under passive multiplexing conditions. A number of parameters have been evaluated, static and dynamic contrast, driving scheme for passive multiplexing, rise and fall response times, dynamic range, and dynamic greyscale.

Liquid crystalline perfluorinated biphenyl benzoates were synthesized and investigated. A highly tilted, neat orthoconic smectic antiferroelectric phase was observed. A homologous series of compounds without and with a single fluorine atom substituted at different positions of a molecular rigid core was investigated by standard methods. Influence of fluorine substitution on physical properties of antiferroelectric smectic phase was discussed as well as influence of fluorination on molecular dipole moment orientation and its value were presented. Decrease in rotational viscosity as a result of fluorine substitution within a molecular rigid core was ascribed to changes of molecular packing.

Novel chiral esters with partially fluorinated alkoxyalkoxy terminal chains are described. Their phase transition temperatures, enthalpies, and electrooptical properties are reported. A helical pitch in pure compounds and their mixtures based on selective reflection of light is also characterized.

Three new pure antiferroelectric materials, synthesized at the Military University of Technology (MUT), were investigated by dielectric means. Clear relaxation modes were detected, i.e., Soft, Goldstone, low frequency in-phase (PL) as well high frequency anti-phase (PH) modes for paraelectric Sm A*phase, ferroelectric Sm C* phase and antiferroelectric Sm CA* phase, respectively. Additionally, a high relaxation mode in Sm CA* was found. The relaxation frequencies fR of the observed modes were calculated from Cole-Cole diagrams.

Chiral liquid crystal phases have been attracting great interest in the past years because of their unique optical properties, such as: selective light reflection, optical dichroizm, ferro- and antiferroelectric behavior. One of the most popular ways of obtaining such materials is an addition of chiral dopants with high helical twisting power to the achiral liquid crystal mixtures. The aim of this paper is to investigate the dependence of helical twisting power on the spacer length and fluorosubstitution in recently prepared chiral three-ring esters with perfluorinated alkanoyloxy unit in a terminal chain.

W-1000 orthoconic antiferroelectric liquid crystal eutectic mixture was prepared in Military University of Technology. This mixture is probably the broadest antiferroelectric mixture, ever prepared. Precise dielectric measurements were performed in a broad temperature range. Some parameters of detected modes and their temperature characteristics are found. It seems that in different temperature regions of orthoconic antiferroelectric liquid crystal different numbers of modes should be anticipated to fit experimental results. Results are discussed with respect to the theoretical model.

Three new antiferroelectric mixtures W-1000, W-1000A and W-1000B and their components W-1, W-2 and B-3 synthesized at Military University of Technology were investigated by dielectric spectroscopy. Typical relaxation modes in smectic phases and one mode in isotropic phase never observed before were detected. Obtained results were discussed in terms of composition of investigated mixtures and molecular structures of their components.

In search of the long pitch, orthoconic antiferroelectric liquid crystalline mixture (OAFLC), the high tilted host mixture with antiferroelectric smectic phase (AFLC) was formulated. The influence of the molecular dipole moment magnitude and orientation on physical properties of the AFLC was tested by doping of the host by three different dopants. The extensive study of the host material and obtained admixtures was done. Results are discussed in the context of the influence of the molecular dipole moment orientation and magnitude of the dopant on the tilt, helical pitch and spontaneous polarization of the phase of obtained mixtures.

Phase transitions temperatures and temperature dependence of helical pitch p for S-(+)-4′-(1-methylheptyloxycarbonyl)biphenyl-4-yl 4-[(4,4,4,3,3,2,2-heptafluorobutoxy)alkoxy] benzoates, and 3-fluoro-, and 2-fluoro-, 2,3-difluoro-benzoates upon length of alkoxy spacer were tested. For etoxy and propoxy spacer the pitch p in antiferroelectric phase is increasing with temperature to maximal value of about 1000 nm in high temperatures region. For pentoxy, hexoxy, and heptoxy spacer the pitch p is longer and reverse temperature dependence is observed. The compounds convenient for formulation of antiferroelectric orthoconic mixture with pitch length of about 2000 nm were selected.

Three different Antiferroelectric Liquid Crystals, synthesized in Military University of Technology were investigated by dielectric means. Some of them are orthoconic. The structures of studied compounds are very similar. The only one difference is presented in rigid core. The position and number of Fluorine atoms in rigid core changes. Very rich dielectric modes are detected with frequencies from 50 Hz up to 40 MHz. In this paper, dielectric spectroscopy of investigated materials is presented.

Two structurally similar homologous series of chiral esters with partially fluorinated alkoxyalkoxy terminal chains are described. Their synthetic routes and mesomorphic properties, such as phase transitions temperatures and enthalpies, are characterized by polarizing optical microscope and differential scanning calorimetry.