S.-L. Wu

Synthesis and ferroelectric properties of chiral swallow-tailed liquid crystals derived from (L)-lactic acid

Three homologous series of chiral swallow-tailed materials derived from (L)-lactic acid were prepared. Structural effects on the mesomorphic and physical properties were investigated in terms of (i) the variation of non-chiral peripheral length chain, (ii) the variation of swallow-tailed groups and straight alkyl chain at the chiral tails, and (iii) lateral halogen substituents in the core of the molecules. The mesophases and their corresponding transition temperatures were identified by optical polarized microscopy and differential scanning calorimetry. The physical properties of the ferroelectric SmC* phases such as switching current, spontaneous polarization and electro-optical response were also measured and compared.

V-shaped switching in ferroelectric liquid crystal mixtures induced by an achiral swallow-tailed material

A new ferroelectric liquid crystal, 1-ethylpropyl (S)-2-[2-fluoro-4-(4′-decyloxybiphenylcarbonyloxy) benzoyloxy] propanoate, F, was synthesized and mixed with an achiral swallow-tailed material, 2-propylpentyl 4-(4′-nonyloxybiphenyl-4-carbonyloxy) benzoate,P, for the preparation of binary mixtures for the study. The binary mixtures gave a phase sequence SmA* -SmC* -SmX*. The electro-optic response of the mixtures in the ferroelectric SmC* phase was investigated. V-shaped switching was observed as the amount of the achiral swallow-tailed material became greater than 20 wt %. This result suggests that thresholdless, V-shaped switching in ferroelectric liquid crystal mixtures can be achieved by mixing a ferroelectric liquid crystal with an achiral swallow-tailed compound.

TGBA phase in a series of propionates containing two stereocenters

Abstract A homologous series of chiral materials, (R)-2-pentyl (S)-2-(6-(4-(4′-alkoxyphenyl)benzoyloxy)-2-naphthyl)propionates (R,S)PmPBNP (m = 7-14), derived from a naphthalene ring as part of the core structure in conjunction with a chiral tail containing two stereocentres has been synthesized for the investigation. The twist grain boundary smectic A (TGBA) and smectic C (TGB*C) phases were characterized by the microscopic textures of compounds packed in two untreated glass slides, Cano wedge cell, or homogeneously aligned cell. It was found that the occurrence of these phases depend remarkably on the nature of alkyl chain length m; in the case of shorter alkyl chain length (m = 7-10), the TGBA phase behaves as a metastable-like phase mediated between N and SA phases in a short temperature range, whereas in the longer chain length (m 11-14), both the TGBA and TGBC phases become thermodynamically stable phases with a wide temperature range. Consequently, this series of chiral materials resulted in two d...

Novel chiral swallow-tailed amide liquid crystals possessing antiferroelectricity

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.

Synthesis and characterization of new series of ferroelectric liquid crystals containing oligooxyethylene spacers

Abstract Four series of ferroelectric liquid crystals containing oligooxyethylene spacers have been synthesized. These obtained liquid crystal compounds were characterized by NMR, differential scanning calorimetry (DSC) and optical polarized microscopy (POM). The properties of the liquid crystalline phase were investigated as a function of spacer units, numbers of core aromatic rings, and different terminal asymmetric moieties. It was found that (i) the phase transition temperature decreased with the increasing oligooxyethylene spacer unit, (ii) the liquid crystalline phases were enhanced in three phenyl ring system than in two phenyl ring system, and (iii) ferroelectric liquid crystals containing different terminal asymmetric moieties exhibited novel mesophase phenomena. A twist grain boundary phase (TGBA phase) was observed in some compounds of this study. Furthermore, a wide temperature chiral smectic Crange including room temperature was achieved.

Antiferroelectric liquid crystals derived from a new optically active (R)-3-ethylmercapto-2-methylpropionic acid

Abstract A new optically active (R)-3-ethylmercapto-2-methylpropionic acid has been synthesized using D(-)—2,10-camphorsultam as a chiral auxiliary. The optical purity of the acid obtained was greater than 98 per cent. Its derivatives, (R)-4-(3-ethylmercapto-2-methylpropionyl)phenyl 4′-alkoxybiphenyl-4-carboxylates (EMMPPmBC; m = 7–16), have been prepared for the investigation of liquid crystalline properties as a function of peripheral alkyl chain length. Optical studies showed that all members exhibited an antiferroelectric S∗cA phase. The results also indicate that a lengthened alkyl chain length is favoured for ScA ∗ phase formation.

Stable frustrated phases in chiral liquid crystals derived from optically active (R)- and (S)-3-ethylmercapto-2-methylpropionic acids

Highly optically pure (R)- and (S)-3-ethylmercapto-2-methylpropionic acids were synthesized by using optically active (D)- and (L)-2,10-camphorsultams as chiral auxiliaries, respectively. Their derivatives, (R)- and (S)-EMMPNmB (m=6-12), were prepared for investigation. Microscopic texture observations demonstrated that the materials possess three stable frustrated phases: BP, TGBA* and TGBC* phases. Interestingly, it was found that the N* phase behaves as an intermediary phase between BP and TGBA* phases in a rather narrow temperature range (calc. 0.5-1.4°C). A study of the racemic mixture, (±)-EMMPNmB (m=10), indicated that the chirality of the molecule could suppress the formation of smectic phases in the heating process. An increase of alkyl chain length favoured the formation of the TGB phases particularly, in accompaniment with a change of TGB phases from monotropic to enantiotropic. Moderate maximum P S values (calc. 14-19 nC cm-2) and apparent tilt angle (calc. 20°) were obtained for the TGBC* phase in a surface stabilized ferroelectric liquid crystal geometry.

Antiferroelectric phase induced by a semi‐fluoroalkane positioned at the chiral tail of a molecule

A novel fluorinated chiral liquid crystal material derived from a newly designed optically active semi‐perfluorinated alkyl chain in the chiral group, (S)‐1‐(2,2,3,3,3‐pentafluoropropyloxy)‐2‐propanol, and a non‐fluorinated homologue derived from (S)‐1‐propyloxy‐2‐propanol, were prepared for comparison of their mesomorphic properties. The investigation of defect textures, switching behaviour and dielectric permmitivity showed that the introduction of a semi‐perfluorinated alkyl chain into the chiral tail of the molecule induces formation of an antiferroelectric phase.

Effect of the variation of swallow-tailed groups on the mesomorphic and electro-optical properties of chiral compounds derived from (S)-2-(6-hydroxy-2-naphthyl)propionic acid

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.

Synthesis and ferroelectric properties of chiral liquid crystals derived from (S)-1-propyloxy-2-propanol

A new optically active chiral moiety, (S)‐1‐propyloxy‐2‐propanol, was designed and synthesized by the treatment of 1‐propanol with (S)‐propylene oxide under basic conditions. Its derivatives, the (R)‐1‐propyloxy‐2‐propyl 4‐[4‐(4‐alkoxyphenyl)phenoyloxy]benzoates, PPmPPB (m = 8–12), were prepared for the investigation of mesomorphic properties. All of the chiral materials displayed enantiotropic SmA* and SmC* phases, and the shorter alkyl chain members (m = 8–11) 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 in polyimide film‐coated homogeneously aligned cells exhibit thresholdless, V‐shaped switching in the ferroelectric phase.