Self-assembly of chiral mesoionic heterocycles into smectic phases: a new class of polar liquid crystal

The molecular design, synthesis and characterization of the first examples of both classical and non-conventional chiral mesoionic (mesomeric + ionic) liquid crystals derived from sydnones are described. The occurrence of chiral smectic phases in these novel compounds was evidenced by optical microscopy, calorimetry and X-ray studies.     

Preparation and characterization of a novel polyimide liquid crystal vertical alignment layer

A series of diamines with a side chain containing rigid biphenyl unit and nonpolar alkoxy side end group [4-alkoxy-biphenol-3′,5′-diaminobenzoate] (Cm-BBDA, m = 4, 6, 12) were synthesized and their chemical structures were confirmed by Fourier Transform Infrared Spectroscopy (FT-IR) and nuclear magetic resonance spectroscopy (¹H NMR). Then three polyimides (PIs) were prepared by copolymerization of pyromellitic dianhydride (PMDA), 4,4′-methylenedianiline (MDA) and Cm-BBDA in N-methyl-2-pyrrolodone (NMP), and chemical structures of all PIs were confirmed by FT-IR. Structural identification of all poly(amic acid)s (PAA) was performed by ¹H NMR. Liquid crystal (LC) cells were fabricated using these PIs as the alignment layer for characterization of the alignment properties of LCs. It was found that the planar alignment was obtained when PI with side chain containing alkoxy side end group of 4 carbon atoms was employed and the vertical alignment was observed when alkoxy side end groups of 6 or 12 carbon atoms were included. A uniform vertical alignment was validated by polarizing microscopy. It was testified that LC vertical alignment possessed high thermal stability.     

Synthesis and thermal properties of side-chain liquid crystalline polyethers with racemic and chiral backbone

Racemic and chiral [(4-cyano-4′-biphenyl)oxy] and [(4-methoxy-4′-biphenyl)oxy]methyloxiranes were prepared from racemic epichlorohydrin or racemic and chiral glycidols and polymerized in dimethylsulfoxide (DMSO) with Bu^tOK as the initiator system. Initial phase identifications were made by differential scanning calorimetry (DSC) and optical microscopy techniques and confirmed by X-ray diffraction measurements. Upon heating, all the monomers show only a crystal–isotropic phase transition. The racemic and chiral [(4-cyano-4′-biphenyl)oxy]methyloxiranes exhibit a nematic and a cholesteric monotropic phase, respectively. Methoxybiphenyl substituted polyethers are crystalline and insoluble in virtually all common solvents. Cyanobiphenyl substituted polyethers are soluble under the same experimental conditions and show enantiotropic liquid crystalline properties. The racemic polymer exhibits a nematic phase, while the optically active polymer forms a cholesteric phase.     

Synthesis and characterization of novel polar-embedded silica stationary phases for use in reversed-phase high-performance liquid chromatography

We have developed a series of new C₁₀ dipeptide stationary phases via a simple and effective synthetic method. The preparation of the new phases involves the synthesis of silanes and the surface modification of silica. Chromatographic evaluations of these columns were performed using the Engelhardt, Tanaka, and Neue test mixtures. The applicability of these new stationary phases was also evaluated using a series of diagnostic probes including acids, bases or neutral compounds and several generic applications. These new C₁₀ dipeptide stationary phases showed excellent hydrolytic stability over a wide pH range. Like other existing amide-embedded columns, these new stationary phases exhibit higher retention for polar and hydrophilic compounds and different selectivity as compared to conventional C₁₈ columns. These new phases are compatible with 100% aqueous mobile phases, and also provide high column efficiency and good peak shapes for both acidic and basic compounds.     

Enlarging the Kerr constant of polymer-stabilised blue phases with a novel chiral monomer

Polymer-stabilised blue phase liquid crystals (PS-BPLC) have attracted many attentions in the area of display and photonic applications because of the superior electro-optical properties. Before application, the problem of high driving voltage should be resolved first. In this report, a new chiral monomer (C5011) has been synthesised and its influence on PS-BPLC was investigated. By adopting this chiral monomer, the Kerr constant of the PS-BPLC could be increased dramatically, which means improved driving capacity can be achieved.     

Generation of frustrated liquid crystal phases by mixing an achiral nematic-smectic-C mesogen with an antiferroelectric chiral smectic liquid crystal

By mixing the achiral liquid crystal HOAB, exhibiting a nematic (N)-smectic-C (SmC) mesophase sequence, with the chiral antiferroelectric liquid crystal (AFLC) (S,S)-M7BBM7, forming the antiferroelectric SmC(a)(*) phase, at least seven different mesophases have been induced which neither component forms on its own: a twist-grain-boundary (TGB(*)) phase, two or three blue phases, the untilted SmA(*) phase, as well as all three chiral smectic-C-type "subphases," SmC(alpha)(*), SmC(beta)(*), and SmC(gamma)(*). The nature of the induced phases and the transitions between them were determined by means of optical and electro-optical investigations, dielectric spectroscopy, and differential scanning calorimetry. The induced phases can to a large extent be understood as a result of frustration, TGB(*) at the border between nematic and smectic, the subphases between syn and anticlinic tilted smectic organization. X ray scattering experiments reveal that the smectic layer spacing as well as the degree of smectic order is relatively constant in the whole mixture composition range in which AFLC behavior prevails, whereas both these parameters rapidly decrease as the amount of HOAB is increased to such an extent that no other smectic-C-type phase than SmC/SmC(*) exists. By tailoring the composition we are able to produce liquid crystal mixtures exhibiting unusual phase sequences, e.g., with a direct isotropic-SmC(a)(*) transition or a temperature range of the SmC(beta)(*) subphase of about 50 K.     

Chirooptical and photooptical properties of a novel side-chain azobenzene-containing LC polymer

Abstract  A novel chiral–photochromic side-chain polyacrylate with azobenzene fragments in the side groups has been synthesised. It was shown that the polymer forms a smectic phase and a cholesteric supramolecular helical structure with selective light reflection in IR spectral range. Thin spin-coated films of the polymer were prepared and their photooptical and chirooptical properties were studied in detail. It was found that UV irradiation of the films led to E–Z isomerization of the azobenzene moieties with high conversion, which is dependent on thermal prehistory of the films. Subsequent action of visible light results in partial recovery of the E-isomer content, whereas annealing leads to the full back conversion. Circular dichroism (CD) measurements revealed formation of the helical supramolecular structure even in the initial spin-coated polymer films. The E–Z isomerization induces complete disruption of helical order in non-annealed films of the polymer, whereas in the smectic phase of the annealed film only a significant decrease in CD values was found. In addition, the photoorientation phenomena induced by polarized light were studied. It was shown that polarized light induces linear dichroism in the films provided by azobenzene group orientation and the dichroism is stable at room temperature for a prolonged time. These combined chirooptical and photooptical features of this novel polymer enable one to consider this multifunctional compound as a promising material for photonics and for optical applications. Graphical abstract  

甾体枝化的壳聚糖液晶合成及其表征

利用壳聚糖分子内的氨基易于进行化学反应的特点,让壳聚糖分子上的氨基与脱氧胆酸上的羧基团连接.由于脱氧胆酸本身是手性的结构,借此探索甾体枝化对壳聚糖液晶的影响.使用红外光谱研究其结构;使用热失重分析仪研究其热性质,并通过偏光显微镜研究了甾体枝化的壳聚糖的液晶性,表现为溶致胆甾型液晶.对壳聚糖进行改性的同时增加了其溶解性和功能性.     

Synthesis and mesomorphism of novel multi-arm liquid crystals with cholic acid as chiral centre linking Schiff base moieties as mesogens

A new series of multi-arm chiral liquid crystals (LCs) D1–D3 were synthesised and characterised. Cholic acid was used as the core and ω-[4-(p-alkoxybenzoloxy)phenoxycarbonyl]valeric acid (B1–B3) was used as the mesogenic arms, containing different terminal substituent X (B1: X= -OCH₃, B2:X= -CH₃, B3: X= -Cl). Their structures and mesomorphic properties were investigated by Fourier-transform infrared spectroscopy, nuclear magnetic resonance hydrogen spectrometer, differential scanning calorimetry, polarised optical microscopy and X-ray diffraction, respectively. The mesogenic B1–B3 displayed smectic B phase. The multi-arm LC D1 displayed cholesteric, while D2 and D3 exhibited nematic phase. The formation of cholesteric phase of D1 was affected by both the chiral core – the bulky cholic acid and the polarity of the terminal substituent of the mesogenic arm. That D1 displayed cholesteric phase but D2–D3 did not indicated that the stronger polarity of the terminal group OCH₃ of D1 played an important part in stabilising the cholesteric phase. The multi-arm LCs D1–D3 all showed ultraviolet activity. The wavelength of maximum absorption of D1–D3 was affected by the terminal substituent of the mesogenic arm.     

Dielectric spectroscopy of unsymmetrical liquid crystal dimers showing wide temperature range TGBA and TGBC* phases

The electrical properties of frustrated twist grain boundary (TGB) phase are a matter of curiosity. Some studies have indicated the existence of soft and Goldstone modes in TGBA and TGBC* phases respectively. However, the experimental results are still not very conclusive. In the present work, we report dielectric studies of wide temperature range TGBA and TGBC* phases of an optically active dimeric compound 4‐n‐decyloxy‐4′‐(cholesteryloxycarbonyl‐1‐butyloxy) chalcone in the frequency range of 1 Hz to 35 MHz for the planar and homeotropic anchoring of the molecules. Two different relaxation processes have been detected for the planar anchoring of molecules in the TGBA and TGBC^* phases. The soft mode like behaviour is obtained due to tilt fluctuation of molecules in the megahertz region for both TGBA and TGBC* phases. Goldstone mode like behaviour due to phase fluctuation of molecules has been detected for the TGBC* phase in the low frequency region (～200–300 Hz). Activation energies for DC conductivity have also been determined for various phases of the material.     

Direct observation of liquid crystal phases under nanoconfinement: A grazing incidence X-ray diffraction study

We have controlled the molecular orientation of nematic and smectic A liquid crystal (LC) phases in a porous anodic aluminium oxide (AAO) film, in which the pore diameter was varied from 20 nm to 100 nm. Surface anchoring to induce planar and homeotropic molecular arrangement was controlled by chemical modification of the AAO inner surface. Direct observation of the molecular orientation of LC phases was performed using grazing incidence X-ray diffraction technique, showing in-plane and out-of-plane molecular orientation, and the corresponding layer orientation. The systematic investigation of LC phases under nanoconfinement will be useful to design various kinds of physicochemical environments to control the orientation of other soft matters.     

Synthesis of novel chiral stationary phases for high-performance liquid chromatography

Three novel chiral selectors 4a-c were synthesized from(S)-amino acids and(R)-1-phenyl-2-(4-methylphenyl)ethylamine.4a-cwere connected to 3-aminopropylsilanized silica gel to be used as the chiral stationary phase for HPLC.Five amino acid derivativesand two pyrethroid insecticides were fairly resolved on these three new chiral stationary phases under normal phase condition.     

Evaluation of novel dendrimer chiral stationary phases using HPLC

Summary The reversed phase chromatographic properties of the [G1]-L-glutamic and ethyl ester-AC-silica (1), [G2]-L-glutamic acid ethyl ester-AC-silica (2) and the [G1]-L-glutamic acidt-butyl ester-AC-silica (3) dendrimer stationary phases were evaluated. Initial studies involved the comparison between these phases with a classic reversed phase (i.e. ODS1) by the separation of a standard reversed phase test mixture composed of dimethylphthalate, nitrobenzene, anisole, diphenylamine and fluorene. Separations were achieved with comparable performance to those obtained with the conventional reversed phase (ODS1). However, it was apparent that the chromatographic selectivity exhibited by the dendrimer stationary phases was different from that of the ODS1 phase. On a per mole basis, the dendrimers exhibited similar (and sometimes greater) affinity for these analytes compared with the ODS1 ligand. Subsequent chromatographic experiments were conducted upon the dendrimer chiral stationary phases using chiral analytes under reversed phase and normal phase conditions. Chiral resolution was not observed.     

Synthesis and mesomorphism of novel star-shaped glassy liquid crystals containing pentaerythritol esters

A new class of star-shaped glassy nematic liquid crystals based on pentaerythritol as a flexible core and ω-[4-(p-alkoxybenzoloxy)phenoxycarbonyl]valeric acid as the side-chain mesogenic arms has been prepared. Their structures and mesomorphism have been investigated in detail.     

Synthesis and characterization of side chain liquid crystalline polymers exhibiting cholesteric and blue phases

A series of cyclosiloxane-based cholesteric liquid crystalline (LC) polymers were synthesized from a cholesteric LC monomer cholest-5-en-3-yl(3β) 4-(2-propenyloxy)benzoate and a nematic LC monomer butyl 4-[4-(2-propenyloxy)benzoxy]benzoate. All the polymers exhibit thermotropic LC properties and show cholesteric phases. Most of the polymers display four types of phase transition behaviour corresponding to glass transition, melting point, cholesteric phase-blue phase transition and clearing point. The mesophase temperature range of the blue phases are as broad as 20°C. The blue phase was confirmed by the apperance of planar textures and cubic packings. With an increase of non-chiral component in the polymers, the clearing point decreases slightly, while the glass transition and melting temperatures change little. In the reflection spectra of the polymer series the reflected wavelength broadens and shifts to longer wavelength with increase of the non-chiral component in the polymer systems, suggesting that the helical pitch P lengthens.     

Microwave-assisted synthesis of novel imidazolium-based ionic liquid crystalline dimers

Microwave promoted synthesis of novel imidazolium-based ionic liquid crystalline dimers containing calamitic-calamitic, calamitic-discotic and discotic-discotic moieties is reported. Classical reactions failed to produce these dimers. The thermotropic liquid crystalline properties of these salts were investigated by polarizing optical microscopy, differential scanning calorimetry and X-ray diffractometry. These salts, except the one having calamitic-discotic units, with bromide as counter ion were found to be mesomorphic over a wide temperature range.     

A comparison of temperature and mobile phase composition effects for bonded liquid crystal and polymeric stationary phases in HPLC

Summary Using two polycyclyic aromatic hydrocarbons as solutes, a comparison is made between a bonded liquid crystal stationary phase and a conventional polymeric C-18 phase. The bonded nematic liquid crystal phase was the silanized form of 4-[4-(allyloxy)benzoyl-oxy]biphenyl and the polymeric phase was Vydac 201TP. Both phases display shape and planarity selectivity as indicated by the results of the variable temperature and mobile phase composition studies. The slot theory of retention can be used to explain these results. However, the liquid crystal phase is more sensitive to molecular geometry, probably due to its more ordered structure on the surface. Variable temperature experiments which compare retention during both heating and cooling provides additional support for this conclusion. With the polymeric bonded C-18 phase, each solute had identical retention at the same temperature during both the heating and cooling cycles. On the bonded liquid crystal phase, measurable differences in retention were observed at identical temperatures depending on whether the column was heated or cooled. This effect is attributed to a degree of partially reversible disordering which occurs as the column temperature was increased. However, conditioning with the appropriate mobile phase can restore the original retention characteristics of the bonded liquid crystal phase.     

Synthesis and liquid crystal properties of a novel family of oligothiophene derivatives

In order to develop novel oligothiophene-based liquid crystals capable of hydrogen bonding, new terthiophene derivatives containing an alkylamide group, N,N′-dialkyl-5,5″-dichloro-2,2′:5′,2″-terthiophene-4,4″-dicarboxamide (DNC_nDCl3T, n=8, 18), N,N′-dialkyl-5,5″-dibromo-2,2′:5′,2″-terthiophene-4,4″-dicarboxamide (DNC_nDBr3T, n=5, 8, 16, 18), or N,N′-dialkyl-5,5″-diiodo-2,2′:5′,2″-terthiophene-4,4″-dica-rboxamide (DNC_nDI3T, n=8, 18), were designed and synthesized, and their thermal behaviour was examined. It was found that DNC₁₈DCl3T, DNC₁₈DI3T and DNC_nDBr3T (n=8, 16, 18) form a smectic A phase and that the alkyl chain length greatly affects liquid crystal phase formation. The absence of liquid crystallinity in the corresponding ester derivatives suggests that intermolecular hydrogen bonding also plays a role in the formation of a liquid crystal phases in the DNC_nDBr3T system.