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1.
ABSTRACT

Novel chiral three-ring (R) enantiomers were synthesised using optically active (R)-(?)-2-octanol. Properties, such as the sequence of phases, the transition temperatures and enthalpies, were tested by a polarising optical microscope and differential scanning calorimeter. An antiferroelectric smectic phase (SmCA*) with a direct transition from the antiferroelectric to the isotropic phase (SmCA*-Iso) was observed for three esters with an achiral C3F7CH2O(CH2)3O– terminal chain. Bi- and multicomponent mixtures with a broad temperature range of the antiferroelectric phase and good electro-optical properties were formulated. Helical pitch of pure esters and mixtures was measured by spectrophotometry method.  相似文献   

2.
The temperature‐ and electric field‐dependent dielectric relaxation and polarisation of a new chiral swallow tailed antiferroelectric liquid crystal, i.e. 1‐ethylpropyl (S)‐2‐{6‐[4‐(4′‐decyloxyphenyl)benzoyloxy]‐2‐naphthyl}propionate (abbreviated as EP10PBNP), were investigated. The electric field‐induced dielectric loss spectra of EP10PBNP revealed electroclinic and anomalous dielectric behaviour in the chiral smectic A (SmA*)–chiral antiferroelectric smectic C (SmCA*) pre‐transitional regime. From an analysis of thermal hysteresis of the dielectric constant, electric field‐induced polarisation and dielectric loss spectra, the appearance of a ferrielectric‐like mesophase is observed followed by an unstable SmCA* phase in the SmA*–SmCA* pre‐transitional regime.  相似文献   

3.
Thermodynamic, dielectric, optical and switching parameters of a single-phase antiferroelectric (AF) liquid crystalline material (S)-(+)-4-(1-methylheptyloxycarbonyl)-2,3-difluorophenyl 4′-[3-(2,2,3,3,4,4,4-heptafluorobutoxy)prop-1-oxy]biphenyl-4-carboxylate have been studied. These studies show wide temperature range (~97.8°C–25.3°C) of AF SmC*A phase in the material. The dielectric studies have been carried out in the frequency range of 1 Hz–35 MHz under planar anchoring conditions of the molecules. The dielectric spectrum of the SmC*A phase exhibits three relaxation modes due to the collective as well as individual molecular processes. Relaxation frequencies of these modes lie in the range of kHz–MHz regions. Relative permittivity of the material (at 10 kHz) varies from ~8.8 at 98.8°C to 9.9 at 41.0°C. Maximum tilt of the molecule in the SmC*A phase is ~43°C. Spontaneous polarisation, switching time and rotational viscosity have also been determined. The maximum value of PS is ~439 nC/cm2 and switching time is the order of 1–5 millisecond, whereas viscosity is moderate.  相似文献   

4.
The fluorinated compound, (S)-4′′-(6-perfluoropentanoyoxyhexyl-1-oxy)-2′,3′-difluoro-4-(1-methylheptyloxycarbonyl)-[1,1′:4′,1′′]-terphenyl, which exhibits antiferroelectric SmCA*, ferroelectric SmC* and paraelectric SmA* phases, has been investigated by polarising optical microscopy, differential scanning calorimetry, X-ray diffraction and frequency-dependent dielectric spectroscopy methods. X-ray studies have revealed that the layer thickness remains almost constant in the SmA* phase but within the SmC* and SmCA* phases it decreases with decreasing temperature, a step jump being observed only at the SmA*–SmC* transition. The tilt angle in the SmCA* phase decreases from 22.2° to 19.5°, and in the SmC* phase it decreases from 18.8° to 5.5°. Spontaneous polarisation is found to be quite high and varies between 74.1 and 118.7 nC cm?2. The variation in ε′ and ε′′ with temperature shows a discontinuous change at the transition temperatures. Goldstone mode relaxation is only observed in the ferroelectric and antiferroelectric phases and is found to be of the Cole–Cole type. The soft mode is observed on application of a bias field near the SmC*–SmA* transition. Neither the soft mode nor the anti-phase azimuthal angle fluctuation mode is observed in SmCA*. Rotational viscosity decreases quite rapidly with temperature but in a different manner in the ferroelectric and antiferroelectric phases. Activation energy for this process is found to be 48.14 kJ mol?1 in the SmC* phase.  相似文献   

5.
We report the dielectric relaxation behaviour in the antiferroelectric SmCA* and ferrielectric SmCγ* phases of the antiferroelectric liquid crystal 4-[5-(4-octloxyphenyl)-2-pyrimidinyl]phenyl 4,4,4-trifluoro-3-(methoxyphenyl)butanoate which shows an antiferroelectric transition at around 88±0.1°C. In the SmCA* phase, two dielectric relaxation modes have been found, namely the usual antiferroelectric Goldstone mode and another arising from molecular rotation around its short axis. In the SmCγ* phase, one dielectric relaxation mode has been observed due to the ferrielectric Goldstone mode. Dielectric increments and relaxation frequencies of the antiferroelectric and ferrielectric phases are estimated from the fits of the Cole–Cole function of the dielectric spectrum. The dependence of the bias field in the ferrielectric phase is also discussed.  相似文献   

6.
Novel chiral swallow-tailed amide materials, N,N-dipropyl-(S)-2-{6-[4-(4-alkoxyphenyl)benzoyloxy]-2-naphthyl}propionamides, DPmPBNPA (m=9-13), have been designed and synthesized for the investigation of mesomorphic properties. The materials DPmPBNPA (m=9-11) display a monotropic phase sequence of I-SmA*-SmCA*-Cr. The antiferroelectric SmCA* phase for the materials was characterized by microscopic texture, switching behaviour, dielectric permitivity and electro-optical response. The measured maximum P s values in the SmCA* phase of the materials are in the range 80–87 nC cm-2.  相似文献   

7.
An achiral swallow-tailed material, 2-propylpentyl 4-(4′-decyloxybiphenyl-4-carbonyloxy)benzoate, p, showing SmA and SmCalt phases was prepared for mixing (by weight percentage) with an antiferroelectric liquid crystal, (S)-MHPOBC, m, for the study. The binary mixture p/15/m85 using (S)-MHPOBC (85%) as a host doped with achiral material (15%) resulted in a phase sequence SmA-SmC*-SmC*A. The electro-optic response of this mixture in the ferroelectric SmC* phase displayed V-shaped switching, while that in the antiferroelectric SmC*A phase displayed a double hysteresis switching. The mixture p85/m15 possessed SmA* and SmC*A phases; V-shaped switching was found in the antiferroelectric SmC*A phase of this mixture. These optical phenomena implied that a binary mixture containing a larger amount of achiral swallow-tailed material and/or possessing relatively lower polarization favours the occurrence of V-shaped switching in the antiferroelectric phase. The results of this work also suggested that thresholdless V-shaped switching in chiral smectic liquid crystals can be achieved by mixing an achiral swallow-tailed material with an antiferroelectric liquid crystal.  相似文献   

8.
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*.  相似文献   

9.
Abstract

The thermal properties of 4-octyloxyphenyl 4-(4-R-3-nitrobenzoyloxy) benzo-ates (1) and 4-(4-octyloxybenzoyloxy)phenyl 4-R-3-nitrobenzoates (2) have been examined, where R = hydrogen, halogens, alkyl and alkoxy groups. The derivatives of compound 1 incorporating hydrogen, halogens, methoxy and nitro groups show a smectic A phase having a bilayer arrangement, and the others with a long alkoxy group show the SA phase with the monolayer arrangement. The derivatives of compound 2 incorporating halogens, and the nitro group show the SA phase with the monolayer arrangement. The alkoxy derivatives show a smectic C phase as well as the nematic phase. The nitro group at the lateral position tends to increase the ratio of the SA-N transition temperature to the N-I. The effect of the nitro group on the smectic properties has been discussed in terms of the structural and electrostatic nature of the nitro group.  相似文献   

10.
Using a photoelastic modulator‐based novel set‐up, the electric field‐induced in‐plane birefringence and the optical rotatory power (ORP) were measured of an antiferroelectric liquid crystalline compound (12OF1M7) in its various phases using 30 µm homeotropic cells. Some specific signatures of the in‐plane birefringence and of the ORP for the various phases are being established. A relatively small threshold field is needed for the unwinding process of the antiferroelectric phase with a unit cell of four layers [SmCA*(1/2)] compared with that for two layers [SmCA*(0)]. On application of the electric field on the high temperature side of the SmCA*(1/2) phase (80.1–81.5°C), a field‐induced phase transition is shown to occur directly to the SmC* phase, whereas on the lower temperature side (79.4–80.1°C) the transition takes place to SmC* via the SmCA*(1/3) phase. The in‐plane birefringence exhibits a critical power law dependence for the SmC*–SmA transition. The ORP changes sign within the temperature range of the phase with a unit cell of three layers, reflecting a change in the handedness during this phase. Using tilted conoscopy, the results for the biaxiality and the apparent tilt angle for a smectic liquid crystal with a tilt angle greater than 18° in the ferroelectric phase are reported. The biaxiality implies the difference in the refractive indices between the two minor axes of the refractive index ellipsoid. The optical transmittance at visible and IR wavelengths for free‐standing films reveal characteristic reflection bands for these phases. The modulated structures of the reflected bands appear just above the SmCA* phase and below SmCA*(1/3); these are possibly due to an easy deformation of the phase by the surfaces.  相似文献   

11.
The electro-optic and complex dielectric behaviour of an antiferroelectric liquid crystal 4-(1-methylheptyloxycarbonyl)phenyl 4′-(n-butanoyloxyprop-1-oxy)biphenyl-4-carboxylate, having chiral SmCA* and hexatic smectic phases, have been investigated. Complex dielectric permittivities were measured as a function of frequency, d.c. bias field and temperature. Spontaneous polarization was measured by the current reversal technique; tilt angle was measured under a polarizing microscope using a low frequency electric field. The electro-optic properties and dielectric behaviour of the material are compared with results obtained by DSC and polarizing optical microscopy. Dielectric relaxation processes in SmCA* and hexatic smectic phases were determined. The dielectric strength at the SmCA* to hexatic smectic phase transition is discussed in terms of coupling between the long range bond orientational order and smectic C director. It seems from the results of spontaneous polarization and dielectric relaxation spectroscopy that the material might possess an additional phase between the SmCA* and hexatic smectic I* phases.  相似文献   

12.
A series of trifluoro-substituted benzoate derivatives: (S)-1-ethylheptyl 4-[4-(4-alkyloxy-3- fluorobenzoyloxy)-3-fluorobenzoyloxy]-2-fluorobenzoates is reported. The short chain members (n = 8 to n = 11) display a direct SmC*A-SmA transition, whereas for longer chains a SmC* phase appears, but no ferrielectric phases are present, and a direct SmCA*-SmC* transition is obtained. The mesomorphic properties were studied by optical microscopy and DSC, and by electro-optical, helical pitch and optical rotatory power measurements. The effect of the number and position of the fluoro substituents, and the influence of the chiral moiety on the mesomorphic behaviour are discussed.  相似文献   

13.
S.-L. Wu  F.-C. Lu 《Liquid crystals》2013,40(11):1517-1523
Three homologous series of chiral swallow-tailed compounds, alkyl (S)-2-{6-[4-(4′-alkoxyphenyl)benzoyloxy]-2-naphthyl}propionates, (S)HNP(p,n,q) derived from (S)-2-(6-hydroxy-2-naphthyl)propionic acid in conjugation with a variety of swallow-tailed groups, attached to the external side of the chiral centre, have been synthesized and their mesomorphic and electro-optical properties studied. Both (S)HNP(p,1,2) and (S)HNP(p,1,3) exhibited an enantiotropic antiferroelectric SmC*A phase. This implys that the swallow-tailed groups in the molecules favour zigzag pairing of the molecules in the smectic phase. The maximum P S values of compounds (S)HNP(p,1,2) in the antiferroelectric phase were measured in the range 21–30 nC cm-2; those of compounds (S)HNP(p,1,3) were in the range 15–23 nC cm-2, indicating that these chiral compounds possess low polarity. The electro-optical response of the compounds in the antiferroelectric SmC*A phase displayed thresholdless V-shaped switching.  相似文献   

14.
A homologous series of chiral liquid crystal compounds, N‐methyl‐N‐pentyl‐(S)‐2‐(6‐(4‐(4‐alkyloxyphenyl)benzoyloxy)‐2‐naphthyl)propionamide, with an amide linkage in a chiral tail was synthesized and their mesomorphic properties studied. All the materials possessed an antiferroelectric smectic C (SmCA*) phase, which was confirmed by observations of microscopic texture, switching current behaviour and electro‐optical responses. The spontaneous polarization, P s, and apparent tilt angle, θ, were also measured. The maximum P s values are in the range of 173–222 nC cm?2, and the maximum θ values are in the range of 26–30°.  相似文献   

15.
New compound showing a direct SmA*–SmCA* phase transition was synthesised. As far as authors know there are a few pure compounds showing para- and antiferroelectric phases without SmC* between them. Direct current (DC) field applied into a planar-oriented cell induces ferroelectric SmC* phase in an investigated compound. Typical for SmC*, Goldstone mode starts to be detectable. DC field also shifts down the temperature of a SmCA* phase creation. Moreover, modes in the appearing antiferroelectic phase are enhanced by DC field. This paper shows and discusses relations between modes detected in SmA*, SmCA* and SmC* (SmC* phase – nucleated by DC field) phases. Parameters of observed modes are calculated using the Cole–Cole relaxation model and a calculation procedure useful especially for high frequency relaxations (higher than 200 kHz).  相似文献   

16.
For 1-[3-fluoro-4-(1-methylheptyloxycarbonyl)phenyl]-2-[4-2,2,3,3,4,4,4-heptafluorobutoxybutoxy)biphenyl-4-yl]ethane (1F7), built of chiral molecules, results of dielectric measurements of liquid-crystalline and solid phases are presented. Rich polymorphism of liquid-crystalline (SmC*, SmC*A and SmI*A) phases as well as of solid (Cr1 and Cr2) phases were observed down to –130°C. At a frequency range from 0.1 Hz to 3 MHz, the relaxation processes were detected in ferroelectric SmC*, antiferroelectric SmC*A and highly ordered SmI*A smectic phases. The mechanism of complex dynamics (moleculear and collective) was identified with the help of the bias field. Vitrification of conformationally disordered crystal phase Cr2 was found in accordance with calorimetric observations.  相似文献   

17.
The syntheses and liquid crystal properties of two novel esters derived from 4-(4-(decyloxy)phenyl)thiophene-2-carboxylic acid and either (±)-oct-1-en-3-yl 4?-hydroxybiphenyl-4-carboxylate or (S)-(+)-oct-1-en-3-yl 4?-hydroxybiphenyl-4-carboxylate are reported. Within the synthesis of the (S)-(+)-oct-1-en-3-yl 4?-hydroxybiphenyl-4-carboxylate, mushroom alcohol, a natural source of chiral oct-1-en-3-ol and a platform molecule, was employed. The phases present within these compounds have been characterised by thermal optical polarising microscopy and differential scanning calorimetry and assigned as SmA, SmC and SmC Alt for the racemic compound and; SmA, SmC* and SmC*A for the enantiomerically pure compound. This is first reported occurrence of a liquid crystalline ester derived from mushroom alcohol, and potential platform molecule, exhibiting SmA*, SmC* and SmC*A phases.  相似文献   

18.
A secondary chiral (R)-(?)-2-alcohol underwent the Mitsunobu reaction with triphenylphosphine, diethyl azodicarboxylate and ethyl 4-hydroxybiphenylcarboxylate, resulting in the desired (S)-(+)-product with high enantiomeric purity (>99% ee), with the chiral branched chain attached to the biphenyl. This method is operationally simple and provides the very important chiral precursor in good yields (62% in dry THF and 72% in dry Et2O). The condensation of the (S)-(+)-acid chloride from this material and a suitable 4-n-alkylthiophenol in toluene in the presence of pyridine or triethylamine furnishes the chiral (S)-(+)-thiobenzoate liquid crystals in good yields (80–83% in pyridine and 65–68% in Et3N). (S)-(+)-4-(1-Methylheptyloxy)biphenyl 4-alkylthiobenzoates are abbreviated (S)-MHOBSn , where n varies from 4 to 10 and denotes the number of carbon atoms in the alkyl chain. DSC, polarizing microscopy and X-ray diffraction showed that the (S)-MHOBSn series possesses a rich phase polymorphism: two highly ordered tilted phases CrG* and SmI*, as well as the ferroelectric smectic C (SmC*) and chiral nematic (N*) phase. In this series, the seldom observed transition between the chiral phases SmI*–SmC* is seen. All the compounds possess stable enantiotropic SmC* and N* phases. The existence of weak intermolecular hydrogen-bonding in (S)-MHOBSn was confirmed by FTIR spectroscopy.  相似文献   

19.
Abstract

Seventeen esters, derived from 4-n-alkoxy-3-fluorophenols and 4-(5-n-alkyl-2-thienyl)benzoic acids, have been prepared and their liquid crystal transition temperatures determined by thermal optical microscopy. On cooling the isotropic liquid, the SA-SC-SA sequence of phases reported for the octyloxy-octyl and octyloxy-nonyl esters has been observed for certain other homologues, principally members of the 4-(5-n-nonyl-2-thienyl)benzoates. For these compounds, the temperature range of occurrence of the intermediate SC phase decreases as the length of the alkoxy chain increases (for the hexyloxy-nonyl to dodecyloxy-nonyl esters) and the Sc phase is absent for the tetradecyloxy-nonyl homologue.  相似文献   

20.
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 SmCA* phase just below the SmA phase. The SmA-SmCA* phase transition has been studied using DSC and dielectric spectroscopy. In the SmCA* 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.  相似文献   

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