Chiral Tail Research Articles

Synthesis and properties of new materials with banana-shaped achiral cores and chiral end groups

New chiral bent-core mesogens, derivatives of 1,3-phenylene bis[4-(alkanyloxyphenyliminomethyl)benzoate], were synthesized with variation of a substituent (X=F, Cl); their antiferroelectric properties are described. The mesomorphic and switching properties were characterized by differential scanning calorimetry, polarizing optical microscopy, triangular wave method, and X-ray diffractometry in the small and wide angle regions. The presence of chiral tails at the terminals of side wings in the bent-core molecules induced a decrease in transition temperature and formation of the switchable SmC* phase in the melt. In addition, the introduction of a lateral halogen substituent in the Schiff's base moiety prevented the regular stacking of the molecules, resulting in the formation of very complex optical textures. The smectic phase with F-substituted PBFDOB and Cl-substituted PBCDOB showed layer spacings of 39 and 38.5 Å, respectively, corresponding to the end-to-end distance of molecules with a bent conformation. Significantly, the smectic phases of PBFDOB and PBCDOB exhibited a period of 179.5 and 131 Å, respectively, compatible with a helical structure with periodicity about 4.6 and 3.4 times the layer spacings.

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.

Synthesis and characterization of new chiral liquid crystalline polyacrylates from L-isoleucine

The synthesis of chiral side chain liquid crystalline polyacrylates with a two-stereogenic centre from L-α-aminoacid is described. The chiral tail is 2-chloroalcohol obtained from L-isoleucine and the spacer group has either four or eleven methylene units. The mesogenic moiety is derived from phenyl benzoate. The stereochemistry of the key intermediate (2S,3S)-(+)-4- [1-(2-chloro-3-methyl)pentyloxy]phenyl benzoate (6) obtained by a Mitsunobu reaction was established by single crystal X-ray analysis. This result indicates that the nucleophilic displacement of chiral diazonium salts proceeds with overall retention of configuration. The liquid crystalline behaviour of polyacrylates P13 and P14 was investigated by DSC, optical microscopy, small angle X-ray scattering and depolarized light scattering. The polyacrylate P13, with eleven methylene units in the spacer, exhibits a chiral smectic A phase whereas the polyacrylate P14, with a spacer containing four methylene units, displays a chiral nematic phase.

Structural Effects on the Mesomorphic Properties of Chiral Liquid Crystal Materials Derived from Optically Active (R)-3-Alkylmercapto-2-methylpropionic Acids

Highly optically pure (R)-3-alkylmercapto-2-methylpropinoic acids were synthesized by using optically active (D)-2,10-camphorsultam as a chiral auxiliary. Three series of homologous derivatives, based on the structure of (R)-6-(3-ethymercapto-2-methylpropionyloxy)-2-naphthyl 4-decyloxybenzoate, (R)2MMPNDB, were prepared for investigating the effect of molecular structure on the mesomorphic properties. The results showed that the extending alkyl chains appended at chiral tail of the molecules have little effect on the existing BP and TGB phases on cooling stage. Investigating halogenated compounds indicated that halogen substituents on the phenyl ring suppress the formation of mesophases, especially TGB phases. The results on the variation of core structures indicated that the naphthalene ring in the core structure of the molecule closely attached to the chiral tails is favorable for the formation of the BP and TGB phases. The magnitudes of spontaneous polarization (Ps) measured for varying alkyl chain at chiral tail of the compounds are approximately in the range of 18 to 23 nC/cm 2 .

Self-assembly of disk-shaped molecules to coiled-coil aggregates with tunable helicity

A disk-shaped molecule with chiral tails is shown to form long fibers of molecular diameter and micrometer length by self-assembly in chloroform. The molecules are derived from crown ethers and contain a phthalocyanine ring. In the fibers, they have a clockwise, staggered orientation that leads to an overall right-handed helical structure. These structures, in turn, self-assemble to form coiled-coil aggregates with left-handed helicity. Addition of potassium ions to the fibers leaves their structure intact but blocks the transfer of the chirality from the tails to the cores, leading to loss of the helicity of the fibers. These tunable chiral materials have potential in optoelectronic applications and as components in sensor devices.

Chiral linear isocyanide palladium(ii) and gold(i) complexes as ferroelectric liquid crystals

A. Omenat, J. Serrano, T. Sierra, D. B. Amabilino, M. Minguet, E. Ramos and J. Veciana, J. Mater. Chem., 1999, 9, 2301 DOI: 10.1039/A903084K

Ferroelectric liquid crystals derived from isoleucine I. Synthesis and characterization

A series of ferroelectric liquid crystals (FLCs), 4 (3-methyl-2-halopentanoyloxy)- 4-hexyloxybiphenyls (3M2XPHOB, X=F for fluorine, C for chlorine, B for bromine) and their racemates (3M2XPHOB-R), were synthesized and characterized. The FLCs contain a chiral tail comprised of alpha -halo acids which are derived from L-isoleucine (DL-isoleucine for the racemates). The mesogens were characterized by high-resolution 1H and 13C NMR and their phase behaviour was studied by optical microscopy and differential scanning calorimetry. The chloro and bromo derivatives show both chiral smectic C (SmC*) phases and smectic A (SmA) phases, while the fluoro derivatives exhibit only a SmA phase. The spontaneous polarization of 3M2CPHOB and 3M2BPHOB were measured in the respective SmC* phases; that of the fluoro derivative was inferred by extrapolating its concentration dependent polarization in an achiral SmC solvent, a racemic mixture of 3M2BPHOB.

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

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 centre could cause a weakening of smectic layer order and result in an occurrence of TGBA* phase. The measured Ps values in the Sc* phase from the isomers, also indicated the absolute configuration of second chiral centre plays an important role in determining the magnitude of spontaneous polarization.

Influence of spacer variation on phase behaviour of liquid crystalline copolymethacrylates containing cholesteryl and S-(-)-4-chloropropionyloxybiphenyl-4-yl groups

Liquid crystalline side group copolymers containing cholesteryl and S-(-)-chloropropionyloxybiphenyl groups were synthesized and investigated by size exclusion chromatography, 1H NMR spectroscopy, polarization microscopy, X-ray diffraction and differential scanning calorimetry. The spacer of the cholesteryl-containing side groups was changed by the substitution of two methylene groups by ether groups. The existence of a cholesteric phase on copolymerization of two monomers containing chiral tail groups, from which the homopolymers exhibit only smectic phases, could be observed. This cholesteric phase only exists over a narrow range of copolymer composition. The temperature dependence of the reflection wavelength for the cholesteric phase was determined. For the cholesteryl-containing homopolymer, an SA bilayer phase was observed, whereas the S-(-)-chloropropionyloxybi2 phenyl homopolymer showed a higher ordered SB phase below an SA monolayer phase. The layer periodicities of the SA phases of the copolymers depend on the composition. The substitution of two methylene groups of the spacer by ether groups led to disappearance of the cholesteric phase. Simultaneously, over a small range of copolymer composition a biphasic region was obtained.

FLCs with a five-membered ring in the mesogenic core

A study has been undertaken of the structure-activity relationship of eight new chiral compounds having either a pyrazole (series P) or an isoxazole (series I) ring as a central bridge in the mesogenic core. The presence of dimers in the pyrazole compounds accounts for their lower P s values in comparison with the isoxazole analogues. The corresponding four beta-diketone precursors have also been studied and these, as expected given their bent molecular shape, show much worse mesomorphic and ferroelectric behaviour. In order to complete the study, the molecular dipoles of the three types of derivative have been determined using AM1 calculations. Two types of chiral tail have been incorporated into the compounds: alkoxy and alkanoyloxy. The latter tail gives rise to the best mesomorphic and ferroelectric properties. A study of the tail conformations by MM2 calculations provides an explanation of these results. The highest P s value (137 nC cm) has been obtained for the isoxazole derivative with the (2S)-2-butyloxypropanoyloxy chiral tail (compound I4). The potential of all twelve compounds as chiral dopants for FLC mixtures has been evaluated by a study of 10 mol% binary mixtures in a standard host system.

Synthesis and Thermal Properties of Ferroelectric Side-Chain Liquid-Crystalline Polysiloxanes Based on Naphthyl Biphenylcarboxylate Mesogenic Groups and Oligooxyethylene Spacers

In this work, three series of ferroelectric side-chain polysiloxanes containing oligooxyethylene spacers and (S)-2-methyl-1-butyl (2S)-2-[6-(4-hydroxybiphenyl-4‘-carbonyloxy)-2‘-naphthyl]propionates, (R)-1-methylheptyl (2S)-2-[6-(4-hydroxybiphenyl-4‘-carbonyloxy)-2‘-naphthyl]propionates, and (2S,3S)-2-chloro-3-methylpentyl (2S)-2-[6-(4-hydroxybiphenyl-4‘-carbonyloxy)-2‘-naphthyl]propionates mesogenic groups were synthesized. The mesomorphic behaviors of three series of ferroelectric side-chain liquid-crystalline polysiloxanes were also studied using differential scanning calorimetry, optical polarizing microscopy, and high-resolution X-ray diffraction measurements. Some of these side-chain polysiloxanes containing four phenyl rings of ester cores (i.e., −Ph−Ph−COO−naphthyl−) and chiral heptyl tail present a smectic A (SA), and a chiral smectic C (Sc*) phase (around 100 °C). Another two series containing four phenyl rings of ester cores and chiral butyl and pentyl chain tail reveal a cholesteric (N*), an SA phase and an Sc* phase. The polymer PS12NC derivative with one unit of oxyethylene spacer (n = 1) of PSn2NC series reveals a N* phase, a twist grain boundary A (TGBA) phase, and a Sc* phase. X-ray investigations reveal that the packing of mesogenic groups for PS02NA, PS02NB, PS02NC with the shortest spacers (n = 0) exhibit a bilayer (two-layer) packing structures. Moreover, polymer PS32NA, PS32NB, PS32NC with the longest spacer chain (n = 3) reveal a monolayer packing structure. However, these two types of packing structure appear simultaneously in PS12NA (n = 1), PS12NC (n = 1), PS12NB (n = 1), and PS22NB (n = 2), depending on the chiral tail length. Results obtained in this study again demonstrate that the tendency toward chiral smectic C mesomorphism increases as the rigidity of phenyl ester mesogens increases via the flexible oligooxyethylene spacers system. Furthermore, the thermal stability of the chiral smectic C mesophase is determined by the flexibility of the chiral tail.

TGBAphase 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 antiferroelectric liquid crystals with a trifluoromethyl group at the chiral center

Abstract The relationship between molecular structure and antiferroelectricity was investigated for the antiferroelectric liquid crystals which did not have any carbonyl moiety in the molecule. A chiral alkyl tail length had influence on phase transition temperature, enthalpy, spontaneous polarization (Ps) and tilt angle. Using a pair formation model of transverse dipole moments in adjacent smectic layers, the relationship was discussed.

Helix twist inversion in the SmC* phase of lactic acid derivatives

Abstract The helix twist inversion in the chiral smectic-C phase was studied in new homologue series of lactic acid derivatives. The temperature of inversion was found to increase with increasing molecular chiral tail. With all studied substances high values of spontaneous polarisation Ps were found which did not reach a saturation on cooling, in spite of saturated tilt angle Θs . Dielectric properties as well as the dielectric relaxation frequency exhibit anomalies around the helix twist inversion temperature. The helix twist inversion phenomena is qualitatively discussed on the basis of a competition between spatial conformers and a thermodynamic model of the SmC* phase.

Synthesis and characterization of new ferroelectric liquid crystals containing a (2S)-2-[6-(4-hydroxybiphenyl-4′-carbonyloxy)-2′- naphthyl] propionate mesogenic group and oligo(oxyethylene) spacers

Abstract Three series of ferroelectric liquid crystals containing a (2S)-2-(6-(4-hydroxybiphenyl-4′-carbonyloxy)-2″-naphthyl)propionate mesogenic group and oligo(oxyethylene) spacers were synthesized. These obtained liquid crystal compounds were characterized by NMR, differential scanning calorimetry (DSC), optical polarized microscopy (POM), and X-ray powder diffraction measurements. Some of these materials containing four phenyl rings of ester cores (i.e. -Ph-Ph-COO-naph-) and chiral heptyl tail exhibited a rich mesomorphic behaviour, a blue phase (BP), a cholesteric phase (Ch), a smectic A (SA), a twist grain boundary A (TGBA), and a chiral smectic C (SC*) phase. Another series containing four phenyl rings of ester cores and chiral butyl and pentyl chain tails revealed only a SA phase and a SC* phase. Moreover, a crystal E phase was observed in the short spacer chain (n = 0 or 1) homologues of three series of compounds. Also, the mesomorphism properties were discussed as a function of spacer units, num...

Synthesis and Thermal Properties of Ferroelectric Side Chain Liquid Crystalline Polysiloxanes Based on the Phenyl Ester Mesogen and Oligo(oxyethylene) Spacers. 1. Phenyl Benzoate and Biphenyl Benzoate Mesogenic Groups

Four series of ferroelectric side chain polysiloxanes containing oligo(oxyethylene) spacers and (2S)-2-methyl-1-butyl 4-(((4-hydroxyphenyl)carbonyl)oxy)benzoate, (2S)2-methyl-1-butyi 4'-(((4-hydroxyphenyl)carbonyl)oxy)-1,1'-biphenyl-4-carboxylate, (2R)-1-methylheptyl 4'-(((4-hydroxyphenyl)-carbonyl)oxy)-1,1'-biphenyl-4-carboxylate, and 4-[(2S,3s)-(2-chloro-3-methylpentanoyl)oxyl]-1,1'-biphenyl-4'-yl benzoate mesogenic groups were synthesized. The mesomorphic behavior of the four series of ferroelectric side chain liquid crystalline polysiloxanes are studied in this work using DSC, optical polarizing microscopy, and high-resolution X-ray diffraction measurements. Some of these side chain polysiloxanes containing three phenyl rings of ester cores (i.e., -Ph-COO-Ph-Ph-) and a chiral butyl tail present a rich mesomorphic behavior : a blue phase (BP), a cholesteric phase (N * ), a smectic A (S A ) phase, a twist grain boundary A (TGB A ) phase, a chiral smectic F (S F * ) phase, and a chiral smectic C (Sc * ) phase over a wide temperature range (around 160 °C). Another series containing three phenyl rings of ester cores and a chiral heptyl chain tail only reveal the S A phase and TGB A phase. The intermediary twist grain boundary phase would display an iridescent Grandjean plane or a filament texture. Results obtained in this study seem to imply that the tendency toward chiral smectic C mesomorphism increases as the rigidity of phenyl ester mesogens increases via the flexible oligo-(oxyethylene) spacer system, and the thermal stability of the chiral smectic C mesophase is determined by the flexibility of the chiral tail.

Structural characterization of the smectic polymorphism of chiral liquid crystalline polysiloxanes containing biphenyl mesogens

Abstract A structural characterization of chiral side chain siloxanes with different average degrees of polymerization, DP n, was performed by X-ray diffraction experiments on powder and oriented fibre specimens. Polymers (DP n = 35) and oligomers (DP n = 4) contained the 4,4′-biphenylene unit with either an (S)-2-methylbutoxy (An, Bn) or an (S)-2-chloro-3-methylbutanoyloxy substituent (Cll). The spacer segment connected to the siloxane backbone had a variable number, n, of methylene groups (n = 5, 8, or 11). Independent of the spacer length and the chiral tail nature, the polysiloxanes underwent the same sequence of phases: C-SF1 (or SI1)-SC1-SA1-I, whereas in the oligosiloxanes the sequence C-SB1-SA1-I (B11) or C-SF1-SC1-I (B5) occurred. The influence of the structure of the polysiloxanes on the formation of the smectic (tilted or orthogonal) mesophases was elucidated. The rather large number of reflections (three or four) detected in the X-ray patterns at low angles, allowed a drawing of the projection...

.beta.-Chlorohydrins vs .alpha.-chloroacids as chiral tails for ferroelectric liquid crystals. MM2 approach. 2

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXT.beta.-Chlorohydrins vs .alpha.-chloroacids as chiral tails for ferroelectric liquid crystals. MM2 approach. 2T. Sierra, M. B. Ros, A. Omenat, and J. L. SerranoCite this: Chem. Mater. 1993, 5, 7, 938–942Publication Date (Print):July 1, 1993Publication History Published online1 May 2002Published inissue 1 July 1993https://doi.org/10.1021/cm00031a011RIGHTS & PERMISSIONSArticle Views42Altmetric-Citations6LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (621 KB) Get e-Alerts Get e-Alerts

Synthesis and ferroelectric properties of some terphenyl derivatives with two terminal substituents of different structures

A new series of terphenyl derivatives with two terminal chiral substituents of different structures have been synthesized. Attachment of a chloro group to the chiral centre promotes the chiral smectic C * mesomorphism. The induced p o and P s values are correlated to the structural features of each chiral tail

Broad Temperature Range Of Chiral Smectic C Phase In Some Ferroelectric Side-Chain Liquid Crystalline Polysiloxanes Containing Oligooxyethylene Spacers

ABSTRACTThe Mesomorphic behaviors of some ferroelectric liquid crystalline monomers and side-chain polysiloxanes studied by X-ray diffraction Measurement, differential scanning calorimeter and polarizing Microscope. All obtained polymers exhibit wide temperature range of chiral smectic C phase including room temperature.These Mesogenic structures contain oligooxyethylene spacers and (S)-2-Methyl-l -butyl chiral tail via a three phenyl ester linkage (i.e. -Ph-COO-Ph-Ph- or -Ph-Ph-COO-Ph-). Two series of monomers with different biphenyl group linkage position were compared. One shows a novel twisted smectic A phase, in addition to the liquid crystalline sequence (Ch→SA→Sc*) obtained between cholesteric phase and smectic A phase. It also presents an unusual smectic A and chiral smectic C phase.All the prepared polymers present smectic Mesomorphism. As the unit of flexible oligooxyethylene spacers increases, the clearing temperature decreases and the stability of the smectic phase also increases.