Novel liquid crystals based on [1]benzothieno[3,2- b][1]benzothiophene

Four series of new [1]benzothieno[3,2- b][1]benzothiophene derivatives have been synthesized. In the non-chiral series a SmA phase occurs, while the chiral series exhibits a rather wide antiferroelectric SmC^A* phase just below the SmA phase. The SmA-SmC^A* phase transition has been studied using DSC and dielectric spectroscopy. In the SmC^A* phase the spontaneous quantities have been measured. The tilt angle shows a typical temperature dependence and the values of spontaneous polarization are rather moderate. The length of the helical pitch increases on increasing the length of the non-chiral alkyl chain.     

New series of chiral ferroelectric liquid crystals with the keto group attached to the molecule core

Two new series of ferroelectric liquid crystals with a keto group attached to the molecular core and a lactate unit as a chiral centre were synthesized and studied. All the compounds exhibit the paraelectric SmA phase and the ferroelectric SmC * phase over very wide temperature ranges and down to room temperature. The main characteristics of the chiral ferroelectric SmC * phase, namely spontaneous polarization, spontaneous tilt angle, and dielectric constant, have been measured to establish their relationship to the length of the terminal chains. The influence of the chiral and non-chiral chain lengths on the helix pitch length is also discussed.     

New series of chiral ferroelectric liquid crystals with the keto group attached to the molecule core

Two new series of ferroelectric liquid crystals with a keto group attached to the molecular core and a lactate unit as a chiral centre were synthesized and studied. All the compounds exhibit the paraelectric SmA phase and the ferroelectric SmC* phase over very wide temperature ranges and down to room temperature. The main characteristics of the chiral ferroelectric SmC* phase, namely spontaneous polarization, spontaneous tilt angle, and dielectric constant, have been measured to establish their relationship to the length of the terminal chains. The influence of the chiral and non-chiral chain lengths on the helix pitch length is also discussed.     

Novel ferroelectric liquid crystals based on fused thieno[3,2-b]furan and thieno[3,2-b]thiophene cores

Several series of new benzofused thieno[3,2-b]furan- and thieno[3,2-b]thiophene-based derivatives have been synthesized and their mesomorphic properties investigated. All the studied compounds exhibit a SmC* phase with very wide temperature interval. Additionally, some types of the compounds show the cholesteric, SmA or blue phase. In the ferroelectric SmC* phase we evaluated physical properties of relevance for possible applications.     

The effect of the alkyl chain length on the mesomorphic properties of new lactic acid derivatives

New series of lactic acid derivatives with alkyl terminal chain have been synthesised and their mesomorphic properties studied. We have varied the length of chiral and non-chiral terminal alkyl chains and found that prolonging both chains has a strong effect on the SmA*–SmC* phase transition. Most of the new materials exhibit only paraelectric SmA* phase; for homologues with a longer non-chiral chain (m ≥ 10), the ferroelectric (SmC*) phase appears below the SmA* on cooling and persists down to a room temperature. The role of the chiral terminal chain in the molecule is quite opposite – only its short length supports the existence of ferroelectric phase. Additionally, a hexatic phase appeared below the SmA*–SmC* phase sequence for several homologues at low temperatures. All materials have been studied using standard experimental techniques (differential scanning calorimetry (DSC), texture observations, polarisation and tilt angle measurements, etc.). Liquid crystalline properties of new materials have been compared with the previously prepared and studied lactic acid derivatives.     

Synthesis and mesomorphic properties of liquid crystalline [1]benzothieno[3,2-b][1]benzothiophene derivatives

Two new series of chiral aliphatic and aromatic esters of 7-decyl[1]benzothieno[3,2-b][1]benzothiophene-2-carboxylic acid were synthesized and their mesomorphic behaviour studied. While the chiral aliphatic esters exhibited only the SmA phase, the antiferroelectric SmC_A* phase was found for esters with chiral 4-hydroxybenzoates; for one homologue a ferroelectric SmC* phase was also observed. Introduction of lateral substituents in the 3-position of the 4-hydroxybenzoic acids (methoxy, fluoro, chloro, and bromo) led to a reduction of the polymorphism and only the SmA phase remained.     

Direct transition from the SmA phase to the tilted hexatic phase in liquid crystals with several lactate units

Compounds with differing numbers of lactate units in the chiral part were synthesized. For all materials, at least two smectic phases were found. In addition to the SmA, the SmC* and/or the tilted hexatic SmI*(F*) phase appear according to the length of the non-chiral alkyl chain. For the shortest non-chiral chain, a direct transition from the SmA phase to the SmI*(F*) phase has been discovered and studied. For compounds with the 2-(S)-methylbutyl alkyl chain and two lactate units in the chiral part the antiferroelectric SmC*_A phase occurs. The ferroelectric character of the hexatic phase has been confirmed even just below the SmC*_A phase.     

Direct transition from the SmA phase to the tilted hexatic phase in liquid crystals with several lactate units

Compounds with differing numbers of lactate units in the chiral part were synthesized. For all materials, at least two smectic phases were found. In addition to the SmA, the SmC* and/or the tilted hexatic SmI*(F*) phase appear according to the length of the non-chiral alkyl chain. For the shortest non-chiral chain, a direct transition from the SmA phase to the SmI*(F*) phase has been discovered and studied. For compounds with the 2-(S)-methylbutyl alkyl chain and two lactate units in the chiral part the antiferroelectric SmC*_A phase occurs. The ferroelectric character of the hexatic phase has been confirmed even just below the SmC*_A phase.     

Synthesis, properties and crystal structure of chiral semiperfluorinated liquid crystals with ferro and anticlinic smectic phases

A new chiral and semiperfluorinated series with ferro and anticlinic properties has been synthesized and characterized. The mesomorphic behaviour has been established on the grounds of both microscopic observations and DSC measurements. The non-chiral intermediate ethyl 4-semiperfluorinated alkyloxybenzoates exhibit SmA phases, unusual for compounds with a single phenyl ring. The final derivatives display SmA, SmC* and in several cases SmC*A phases. The longer fluorinated chains favour the SmA and SmC* phases at the expense of the SmC*A phase. Electro-optical measurements were carried out with the classical SSFLC geometry. The spontaneous polarization and tilt angle at saturation are higher than those of the hydrogenous homologues, around 140 nCcm-2 at 40 degrees C. One compound of the series, the 4,4,5,5,6,6,7,7,8,8,8-nonafluoroheptyloxy derivative, C36H35O7F9, Mx=750.6 g mol-1, crystallizes in the triclinic system, space group P1 with four independent molecules in the asymmetric unit (Z=4). The molecules are arranged in a head-to-tail fashion with two molecules oriented in the same direction and the two others in the opposite direction. They give rise to sheets with a smectic C-like arrangement. The final reliability factors were R=0.117 and wR=0.134; the goodness of fit was S=1.366.     

Synthesis,properties and crystal structure of chiral semiperfluorinated liquid crystals with ferro and anticlinic smectic phases

A new chiral and semiperfluorinated series with ferro and anticlinic properties has been synthesized and characterized. The mesomorphic behaviour has been established on the grounds of both microscopic observations and DSC measurements. The non-chiral intermediate ethyl 4-semiperfluorinated alkyloxybenzoates exhibit SmA phases, unusual for compounds with a single phenyl ring. The final derivatives display SmA, SmC* and in several cases SmC*A phases. The longer fluorinated chains favour the SmA and SmC* phases at the expense of the SmC*A phase. Electro-optical measurements were carried out with the classical SSFLC geometry. The spontaneous polarization and tilt angle at saturation are higher than those of the hydrogenous homologues, around 140 nCcm-2 at 40 degrees C. One compound of the series, the 4,4,5,5,6,6,7,7,8,8,8-nonafluoroheptyloxy derivative, C36H35O7F9, Mx=750.6 g mol-1, crystallizes in the triclinic system, space group P1 with four independent molecules in the asymmetric unit (Z=4). The molecules are arranged in a head-to-tail fashion with two molecules oriented in the same direction and the two others in the opposite direction. They give rise to sheets with a smectic C-like arrangement. The final reliability factors were R=0.117 and wR=0.134; the goodness of fit was S=1.366.     

Lactic acid derivatives with terphenyl molecular core

New lactic acid derivatives, based on terphenyl molecular core laterally substituted by chlorine atom, have been synthesised and their liquid crystalline properties studied. We varied the molecular structure by prolonging the non-chiral chain and analysed the mesogenic properties with respect to its length. We found that all new compounds reveal the SmA*–SmC* phase sequence in an extremely broad temperature interval. The experimental techniques, namely the polarising optical microscopy, differential scanning calorimetry, x-ray diffraction and helical pitch measurements, have been applied to establish the physical properties. Studied compounds exhibit very high values of the spontaneous polarisation and the tilt angle grows continuously on cooling up to 42°. The pitch values drop down when prolonging the molecular non-chiral chain.     

Synthesis and mesomorphic properties of chiral liquid crystals having thiolactate groups

A homologous series of chiral thiolactate liquid crystals, alkyl 2-[4-(4-decyloxyphenyl)benzoyloxyphenyloxy]thiopropionates, ADBPT-n (n=2-6), was prepared from (R)-2-(4-hydroxyphenoxy)propionic acid. Structural effects on the mesomorphic and physical properties were investigated in terms of variation in the length of alkyl chain attached to the thiolactate group. The mesophases and their corresponding transition temperatures were identified by polarizing optical microscopy and differential scanning calorimetry. Compound ADBPT-4 exhibited SmA* and SmC* phases, whereas other compounds in the series exhibited the SmA* phase along with unidentified SmX₁* and SmX₂* phases. The maximum P_s value measured for ADBPT-4 in the SmC* phase was 17.5 nC cm^-2, suggesting the polarization of the material is rather low. The tilt angles were also measured, reaching a maximum of 48 degree.     

Ferroelectric liquid crystals derived from (S)‐2‐(6‐methoxy‐2‐naphthyl)propionic acid with non‐fluorinated or semi‐fluorinated alkanes at a chiral terminal chain

Two series of ferroelectric liquid crystals derived from (S)‐2‐(6‐methoxy‐2‐naphthyl)propionic acid, with non‐fluorinated or semi‐perfluorinated alkanes positioned at a chiral terminal chain, have been synthesized and characterized by differential scanning calorimetry, polarizing optical microscopy and electro‐optical measurements. The non‐fluorinated compounds, 1‐hexyl (S)‐2‐{6‐[4‐(4‐alkanoyloxyphenyl)benzoyloxy]‐2‐napthyl}propionates exhibit rich mesomorphism—the BP_II, N*, TGB_A*, SmA* and SmC* phases. The fluorinated compounds display only the SmA* and SmC* phases, suggesting that the fluorination promotes the formation of smectic phases. In addition, the SmA* and SmC* phases of the fluorinated compounds have enhanced thermal stability as compared with the corresponding phases of the non‐fluorinated compounds. The spontaneous polarization (P _s values) for the non‐fluorinated compounds are higher than those of the fluorinated compounds at any reduced temperature below the SmA*–SmC* transition. The electro‐optical responses measured for these compounds in the ferroelectric phase displayed thresholdless, V‐shaped switching.     

Novel ferroelectric liquid crystals based on fused thieno[3,2‐b]furan and thieno[3,2‐b]thiophene cores

Several series of new benzofused thieno[3,2‐b]furan‐ and thieno[3,2‐b]thiophene‐based derivatives have been synthesized and their mesomorphic properties investigated. All the studied compounds exhibit a SmC* phase with very wide temperature interval. Additionally, some types of the compounds show the cholesteric, SmA or blue phase. In the ferroelectric SmC* phase we evaluated physical properties of relevance for possible applications.     

Synthesis and characterization of a novel liquid crystal series with tribenzoate cores and monofluoro-substitution on the phenyl ring near the chiral chain

Two new chiral series, with benzoate cores and monofluoro-substitution in positions 2 and 3 of the first phenyl ring near the chiral chain, have been synthesized and characterized. The mesomorphic properties have been analysed by optical microscopy, differential scanning calorimetry and electro-optical measurements. The first series (I_c) displays a very rich polymorphism including SmA, SmC*_α, SmC*, SmC*_FI, SmC*_A phases, whereas the second (I_b) does not exhibit the SmC*_A phase, and moreover only displays the SmA phase for short alkoxy chains. The effect of the position of the fluoro substituent and the influence of the alkoxy chain length on the mesomorphic behaviour are discussed.     

Synthesis and ferroelectric properties of chiral swallow-tailed liquid crystals derived from (S)-2-[1-(2-ethylbutoxy)]propanol

(S)-2-[1-(2-Ethylbutoxy)]propanol was designed and synthesized as a chiral building block for the preparation of chiral liquid crystals. Its derivatives, the (S)-2-[1-(2-ethylbutoxy)]propyl 4-[4-(4-alkoxyphenyl)phenoyloxy]benzoates, EPmPPB (m = 8-12), were prepared and their mesomorphic phases investigated. The results showed that the chiral materials displayed enantiotropic SmA* and SmC* phases, while those with shorter alkyl chains (m = 8-10) displayed an additional unidentified SmX* phase. The switching current, spontaneous polarization, tilt angle, dielectric constant and electro-optical response for the materials in the ferroelectric SmC* phase were measured. The electro-optic responses of the materials in polyimide film-coated, homogeneously aligned cell exhibit thresholdless, V-shaped switching in the ferroelectric phase.     

Dielectric spectroscopy of a smectic liquid crystal

Complex dielectric spectroscopy (frequency range 5 Hz–13 MHz) has been used to analyse the frequency, temperature and bias‐field dependences of the molecular dynamics of a very high‐spontaneous‐polarization ferroelectric liquid crystalline material exhibiting SmA, SmC* and unknown SmX smectic phases. Different smectic phase transition temperatures have been observed from the study of the temperature dependence of the dielectric strength and the relaxation frequency. The phase transition temperatures (crystalline to isotropic phases) have also been described very accurately from the temperature‐dependent symmetric and asymmetric shape parameters of the relaxation function and also the dc conductivity. In a planar aligned cell, two symmetric modes (Goldstone mode and domain mode) have been observed in both the SmX and SmC* phases. One asymmetric mode (X‐mode) observed in the SmC* and SmA phases could be related to the interaction of dipoles of the ferroelectric liquid crystals being affected by the surface of the cell. The soft mode, which usually appears very close to the SmC*–SmA phase transition was not observed until the bias field was applied. The second order nature of the SmC*–SmA phase transition was revealed.     

Chiral Liquid Crystals Synthesized from 2(S)‐[2(R)‐Methylhexyloxy]Propanol and its (S,S)‐Diastereomer

Two new chiral alcohols, 2(S)‐[2(R)‐methylhexyloxy]propanol ( 5 ) and 2(S)‐[2(S)‐methylhexyloxy]propanol ( 6 ), were prepared from the corresponding propionic acid ethyl ester 1 and 2 in the presence of sodium borohydride. They were used as the chiral moiety for the synthesis of two diastereomeric liquid crystals 7 and 8 . Both of them exhibit the phase sequence I‐SmA‐SmC*‐SmX‐Cr. The mesogenic properties of the (S,S)‐diastereomer 8 are more unique in comparison with those of the (S,R)‐diastereomer 7. It possesses not only lower SmA and SmC* phase transition temperature, 103 °C vs. 112 °C for SmA phase and 31 °C vs. 65 °C for SmC* phase, but wider SmA and SmC* phase range, 40 °C vs. 31 °C for SmA phase and 72 °C vs. 47 °C for SmC* phase. The diastereomer 8 also has a larger Ps value than that of 7, 24 vs. 15 nC cm^?2 measured at Tc ‐ T = 10 °C. The difference in these mesogenic properties is discussed by comparing their conformation difference at the molecular part of benzoate.     

An investigation of the synthesis of chiral LCs based on the [1,2,3]-triazole ring

The design and synthesis of chiral liquid crystalline compounds based on the [1,2,3]-triazole heterocycle using the click chemistry modular approach is presented. The target compounds showed LC phases of type SmA, SmC* and helical N* (cholesteric). Mesomorphic behaviour was determined by polarizing optical microscopy and differential scanning calorimetry. Contact experiments indicated a right-handed helix for the macrostructure of the cholesteric phase.     

Dielectric properties of four room temperature ferroelectric and antiferroelectric multi-component liquid crystalline mixtures

Dielectric properties of four recently formulated room temperature multi-component liquid crystalline mixtures with paraelectric (SmA*), ferroelectric (SmC*) and antiferroelectric (SmC*_A) phases have been studied as a function of temperature and frequency. Under planer anchoring condition, dielectric spectroscopy revealed all the characteristic modes: low frequency P_L and high frequency P_H mode in SmC*_A phase, Goldstone mode (GM) in SmC* phase and soft mode (SM) in SmA* phase. Dielectric behaviour has also been studied under the application of DC bias electric field. With bias electric field, we have been able to study the soft mode dielectric behaviour in the SmC* phase. An unknown high frequency mode (X-mode) with and without bias is also observed in SmC* phase. Dielectric results are explained in the light of generalised Landau theory. The mixtures show very high soft mode electroclinic coefficient in the SmA* phase in addition to fast switching in SmC*_A and SmC* phases [30].