Shune‐Long Wu

Mesophases Induced by Hydrogen Bonds between Nonmesogens

Abstract Nematic phases were obtained by mixing 4-methoxy-4′-stilbazole with structural isomers of methyl-, methoxy-, and halo-benzoic acid derivatives, all the components are rod-like nonmesogens. It was shown by NMR, IR, uv-vis and fluorescent spectroscopic studies that the hydrogen bonds played the central role. Enantiotropic with wide temperature ranges were observed for the mixtures of 4-substituted benzoic acids. The stability of induced mesophase decreased for the mixtures of 3- and 2-substitutions.

Synthesis and ferroelectric properties of new chiral liquid crystals derived from (S)‐lactic acid with alkoxyethanols

A homologous series of chiral materials derived from (S)‐lactic acid with alkoxyethanols has been synthesized and their mesomorphic properties investigated. The mesophases and their corresponding transition temperatures were identified by differential scanning calorimetry and polarizing optical microscopy. The spontaneous polarization and electro‐optical response of ferroelectric SmC* phase are measured and reported.

Synthesis and mesomorphic properties of chiral liquid crystals derived from (S)-lactic acid with 3-pentanol

The chiral swallow-tailed liquid crystals, 1-ethylpropyl (R)-2-[4-(4′-alkoxybiphenylcarbonyloxy)-phenoxy]propionates, EPmPBPP (m = 8−12), were prepared by using chiral (S)-lactic acid with 3-pentanol as starting materials. Mesophases and their corresponding transition temperatures were determined by polarizing microscopic textures and DSC. The results showed that all the chiral materials exhibited enantiotropic BP, N*, TGBA*, SmA*, and SmC* phases. Spontaneous polarization, dielectric constant and electro-optical response for the materials in the ferroelectric SmC* phase were investigated. It was noted that the electro-optical response of transmittance versus applied voltage obtained from the ferroelectric phase of material EPmPBPP (m = 10) displayed V-shaped switching, while that of other materials displayed the typical characteristics of ferroelectric hysteresis switching or U-shaped switching.

Synthesis and mesomorphic properties of fluoro‐substituted chiral liquid crystals derived from (S)‐lactic acid with alkoxyethanols

A homologous series of fluoro‐substituted chiral liquid crystals derived from (S)‐lactic acid and alkoxyethanols were prepared for investigation. Mesophases and their corresponding transition temperatures were identified by polarized optical microscopy and differential scanning calorimetry. The compounds exhibit a broad temperature range in the ferroelectric chiral smectic C (SmC*) phase; in particular, compounds with shorter alkyl chain lengths have an SmC* phase at ambient temperature. The physical properties of the ferroelectric SmC* phase, such as switching current, spontaneous polarization, optical tilt angle and electro‐optical response, were also measured. The effects of fluoro substituent on the mesophases and physical properties of the chiral liquid crystals are discussed.

Effect of core structures and swallow-tailed groups on the mesomorphic properties of chiral liquid crystals derived from (L)-lactic acid

A homologous series of chiral swallow-tailed materials, I(p,q,m,n), derived from (L)-lactic acid was synthesized for investigation of the effects of variation of the molecular core structure and the terminal swallow-tailed group on the formation of mesophases. The mesophases and their corresponding transition temperatures were identified by polarizing optical microscopy and differential scanning calorimetry. The results indicate that the variations of the core structure and of the methylene group between the chiral centre and the swallow-tailed group, have a remarkable effect on the appearance of mesophases; change in length of the swallow-tail group has less effect. The spontaneous polarization and dielectric constant in the ferroelectric SmC* phase were also measured.

Synthesis and Characterization of Ferroelectric and Antiferroelectric Liquid Crystals Derived from (2S)-2-(6-Hydroxy-2-Naphthyl) Propionic Acid

Abstract A new series of chiral materials, hexyl(2s)-2-(6-(-4-(4′-alkoxyphenyl)benzoyloxy)-2′-naphthyl)propionates (HmPBNP; m = 6-18) had been prepared and their liquid crystalline properties were investigated as a function of alkyl chain length. These chiral materials exhibited novel ferroelectric Sc* and antiferroelectric ScA* phases and a propensity to the formation of the ScA* phase was found at longer alkyl chain lengths (m= 10, 12 - 18). An odd-even effect of the threshold voltage as a function of alkyl chain length for compounds HmPBNP (m= 12-16) possessing antiferroelectricity was observed. Spontaneous polarization and transverse dipole moment were also measured and are discussed in terms of the elongated alkyl chain length.

Anomalous behaviour in the SmA*–SmCA* pre‐transitional regime of a chiral swallow‐tailed antiferroelectric liquid crystal

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.

Antiferroelectric liquid crystals having a semi‐fluorinated alkane positioned at the chiral tail

An optically active semi‐fluorinated alkanol, (S)‐1‐methyl‐2‐(2,2,3,3,3‐pentafluoropropyloxy)ethanol, was prepared by the treatment of 2,2,3,3,3‐pentafluoropropanol with (S)‐propylene oxide under basic conditions. This alkanol was used as a chiral building block for the synthesis of a series of novel chiral materials, the (R)‐4‐[1‐methyl‐2‐(2,2,3,3,3‐pentafluoropropyloxy)ethyloxycarbonyl]phenyl 4′‐alkyloxybiphenyl‐4‐carboxylates, MPFPECPmBC (m = 8–12), that have a semi‐fluorinated alkane positioned at the chiral tail. It was found that all the materials possess enantiotopic SmA*, ferroelectric SmC* and antiferroelectric phases. The basic electro‐optical properties of the chiral materials in the SmC* and phases were measured. The results show that the maximum P s values are in the range 69–92 nC cm−2 and the maximum apparent title angles are in a range of 24°–33°.

Effect of Absolute Configuration on the Formation of TGBA* Phase in Liquid Crystallines Containing Two Stereogenic Centres

Abstract Our previous work has shown that a homologous series of chiral materials containing two sereogenic centres, (R)-2-pentyl (S)-2-(6-(4-(4-alkoxyphenyl)benzoyloxy-2-naphthyl)propionates (R,S)PmPBNP (m=7−14). exhibited TGBA* phase. To understand the effect of relative configuration of two stereogenic centres at chiral tail on the appearance of TGBA* phase, two stereoisomers of (R,S)P11PBNP, (S,S)P11PBNP and (±,S)P11PBNP were synthesized and their mesophases investigated. The results showed that both isomers also possessed TGBA* phase with the phase sequence of I-N*-TGBA*-SA*-Sc*-C, The temperature range of TGBA* phase in (R,S)-isomer was significantly larger than that in (S,S)-isomer, indicating the stability of TGBA* phase was affected by the relative spatial configuration of the second chiral centre at chiral tail. In addition, the temperature range of TGBA* phase in (±,S)-isomer was larger than (S,S)-isomer, suggesting that an introducing methyl branched group at the external side of mono chiral c...

Effect of the semi‐fluorinated chiral alkane on the formation of the antiferroelectric phase

Two structurally similar homologous series of chiral liquid crystals derived from semi‐fluorinated and non‐fluorinated alkanes positioned at a chiral terminal chain have been synthesized and characterized by differential scanning calorimetry, polarizing optical microscopy and electric‐optical measurements. It was found that there are two semi‐fluorinated materials in the series I‐m (m = 8, 10), that exhibit ferroelectric SmC* and antiferroelectric phases. The corresponding non‐fluorinated materials II‐m (m = 8, 10), however, display only the SmC* phase, suggesting that the fluorinated materials encourage the formation of the antiferroelectric phase. The spontaneous polarization (P s) and apparent tilt angle (θ) were measured, showing that the semi‐fluorinated materials have higher P s and θ values than non‐fluorinated materials at any reduced temperature below the SmA*–SmC* transition.