Photochromic chiral liquid crystalline systems containing spiro-oxazine with a chiral substituent I. Synthesis and characterization of compounds

Photochromic acrylates containing both biphenylene and spiro-oxazine moieties with a chiral substituent and the related polymers were prepared and yielded photochromic chiral liquid crystalline systems. The photochromic acrylates containing both an undecamethylene group and a (2S, 3S)-2-chloro-3-methylpentanoyloxy group (A11SOP) or a (-)-menthoxyacetoxy group (A11SOM) gave a supercooled mesophase; the latter reflected right-handed visible light (blue colour) at room temperature. On the other hand, the photochromic acrylate containing both the (R)-(-)-2-methylpropylene and (2S, 3S)-2-chloro-3-methylpentanoyloxy groups (A3SOP) showed no mesophase. The related homopolymers, PA11SOP and PA11SOM, did not exhibit mesophases because of steric hindrance between the side groups of the polymers. However, only PA11SOM exhibited shear-induced birefringence under 100-104°C. Several copolymers consisting of the nematogenic monomer, 4-[4-(6-acryloyloxyhexyloxy)benzoyloxy]benzonitrile (A6CN), and A11SOP or A11SOM possessed a smectic phase due to reduction of the steric hindrance between the potentially smectogenic A11SOP or A11SOM moieties.     

Photochromic chiral liquid crystalline systems containing spiro-oxazine with a chiral substituent II. Photoinduced behaviour

The photoinduced behaviour of low molecular mass liquid crystalline (LC) systems doped with the chiral photochromic spiro-oxazine, 9'-{5-(-)-menthoxyacetoxy-1,3-dihydro-1,3,3-trimethylspiro[2H-indole-2,3'-[3H]naphth-[2,1 -b][1,4]oxazine]} 4-[11-(tetrahydro-2-pyranyloxy)undecyloxy]biphenyl-4'-carboxylate (THP11SOM) was observed by means of transmittance measurements at 21°C. The experimental results revealed that the ring-opened merocyanine form of THP11SOM resulting from the photochromism first disturbed the helical planar orientation of the LC molecules and then induced a new helical pitch. The magnitudes of both the disturbance in orientation of the LC molecules and the shift in the helical pitch were significantly influenced by the concentration of THP11SOM. The photoinduced behaviour was reversible due to the photochemical and thermal back reaction of the THP11SOM. In addition, the effect of UV light on the nematic-isotropic transition temperatures of the mixtures with or without a hindered amine light stabilizer was studied.     

Synthesis and mesomorphic properties of novel fishbone-like liquid crystalline polysilsesquioxanes VI. Fishbone-like,ester-based liquid crystalline polysilsesquioxanes

Two novel kinds of fishbone-like, ester-based, liquid crystalline, random copolysilsesquioxanes, LC₁-CH₃-P and LC₂-CH₃-P, have been synthesized for the first time by stepwise coupling polymerization (SCP) from trichlorosilane monomers (RSiCl₃) containing mesogenic ester groups, using three main steps including preaminolysis, hydrolysis and polycondensation. Two new monomers 4-(11-trichlorosilylundecloyloxy)phenyl 4-methoxybenzoate (M₁) and 4-(3-trichlorosilylpropoxy)phenyl 4-methoxybenzoate (M₂) have been synthesized by hydrosilylation reaction of trichlorosilane and the mesogens 4-n-undecenoyloxyphenyl 4-methoxybenzoate and 4-allyloxyphenyl 4-methoxy-benzoate, respectively, in the presence of dicyclopentadienylplatinum(II) chloride (Cp₂Ptcl₂) catalyst. The structures and mesomorphic properties of LC₁-CH₃-P and LC₂-CH₃-P were investigated by FTIR, ¹H NMR, ¹³C NMR, ²⁹Si NMR, gel permeation chromatography, polarizing optical microscopy, differential scanning calorimetry and X-ray diffraction. It is proposed from the characterization data that these two polymers not only have an ordered ladder-like, double main chain, but also show thermotropic smectic behaviour with high clearing points and wide mesophase ranges (ΔT), which may hold promise for potential applications as highly stable gas chromatographic stationary phases.     

Synthesis and physical properties of high birefringence phenylacetylene liquid crystals containing a cyclohexyl group

We have synthesized new phenylacetylene-based liquid crystals containing a cyclohexyl or cyclohexylethyl group and evaluated their physical properties in order to develop a range of materials having high value of birefringence. The cyclohexyl-containing compounds exhibited nematic behaviour near room temperature and moderate values of δn of around 0.3. The cyclohexylethyl-containing compounds had a very wide nematic range with a high T_NI and very high values of δn of over 0.4. They also exhibited low viscosities. The order parameter was not affected by introducing either a cyclohexyl or a cyclohexylethyl group and the values of δn based on calculated polarizabilities were obtained experimentally.     

Synthesis and characterization of main chain liquid crystalline ionomers containing sulphonate groups

A series of main chain liquid crystalline ionomers containing sulphonate groups pendent to the polymer backbone were synthesized by an interfacial condensation reaction of 4,4′‐bis(1,10‐sebacyloxo)benzoic acid, brilliant yellow (BY), and 4,4′‐biphenyldiol. 4,4′‐Bis(1,10‐sebacyloxo)benzoic acid exhibited nematic schlieren texture during heating and cooling. The ionomers are thermotropic liquid crystalline polymers and thermally stable to about 270°C. They exhibit broad mesophase regions over a range of 220°C and the same nematic mesomogen with a colourful thread texture as B₀‐LCP, which implies that the introduction of an ionic group did not change the texture of the B₀‐LCP. However, the thermotropic liquid crystalline properties were somewhat weakened when the concentration of BY was more than 5%. The inherent viscosity in N,N‐dimethylformamide solution suggested that intermolecular associations of sulphonate groups occurred at low concentration, and intermolecular associations predominated at higher concentration.     

Discotic liquid crystalline materials for potential nonlinear optical applications: synthesis and liquid crystalline behavior of 1,3,5-triphenyl-2,4,6-triazine derivatives containing achiral and chiral alkyl chains at the periphery

As a novel approach to nonlinear optical materials, new octupolar discotic liquid crystalline materials 1,3,5-triphenyl-2,4,6-triazine derivatives containing achiral alkyl chains (5a) and chiral alkyl chains (5b) at the periphery were synthesized. The former exhibits an ordered hexagonal columnar mesophase, whereas the latter displays a rectangular columnar mesophase. The negative exciton splitting observed in the CD spectrum of a thin film of 5b suggests that it has a left-handed helical structure within the column.     

Characterization of a new chiral antiferroelectric liquid crystal with a lateral bromo substituent

In this paper we present the characterization of a new chiral mesogen with a lateral bromo substituent. The identification of the various smectic phases is achieved by texture observation, miscibility studies and DSC. The optic and electro-optic properties are also investigated. The real part of the complex dielectric permittivity as a function of the temperature was also measured in the planar geometry for thin samples. The dielectric behaviour will be qualitatively discussed on the simple assumption of different anchorings. These results point out the importance of anchoring conditions in relation to the macroscopic properties observed in very thin cells of antiferroelectric liquid crystals.     

Conductive liquid crystalline compounds having a piperazine structure

New conductive thermotropic liquid crystalline materials having a piperazine ring in the central core: 1-[4-(9-decenyloxy)phenyl]-4-alkylpiperazines (6) were synthesized. The mesomorphic behaviours of these compounds and their conductivity in the liquid crystal phase were measured. The principal features of these compounds are to exhibit a smectic B phase around room temperature (for example 6: Cr 50 SmB 81 I, °C) and to exhibit a large dark current (6d: 430 μA cm^?2, applied voltage 20 V, at 70°C) in the smectic B phase.     

Synthesis and properties of chiral azo-liquid crystalline terpolymer containing cyano mesogenic units

A series of side-chain cholesteric polysiloxanes (PQ) were synthesised with poly(methyl--hydrogeno)siloxane, cholesterol (4-allyoxybenzoate) (M₁), and 4-hydroxyphenyl-4(allyloxy) phenylpropanoate (M₂), 4-allyloxy-4 ‘-cyanobiphenyl (M₃). Then azo-containing chiral liquid crystalline polymer (PZ) were synthesised with PQ and 4-(4-hexyloxyphenylazo) benzoic acid (M₄) by esterifying catalysed by 4-dimethylaminopyridine which is a new synthetic way. The chemical structures of monomers and polymers were confirmed by conventional spectroscopic methods and test methods for liquid crystal properties. The photo-induced isomerisation of the polymer is investigated by UV–vis spectroscopy. Weight lost temperatures (5%) for all polymers were greater than 298°C. The results showed that the introducing of azo moieties makes the polymer more stable on thermo dynamics. The transition temperatures of the polymers PQ and PZ exhibited some regularity as the change of ingredients of polymers. PQ series showed Grandjean textures and PQ₁–PQ₅ exhibited blue selective reflection in the visible light region. PZ₁–PZ₅ also showed Grandjean textures and the texture colour of the polymer turned to red and colourful with green and blue due to increasing contents of azo moiety, and yellow selective reflection in the visible light region were observed. The molecular design introducing shorter and harder part into chiral polymerisation system is favourable to the appearance of selective reflection. All polymers turned out right-handed optical activity due to having the same cholesteric group, the photo-responsive behaviours of the PZ series were also investigated.     

Optical and thermal properties of unsymmetrical liquid crystalline compounds based on isoxazole

The thermal and optical properties of two series of unsymmetrical liquid crystalline compounds based on an isoxazole ring are described. Of these materials, 3–7 and 8–12 displayed strong absorption at 285 nm and a weak blue fluorescence in solution at around 377 nm, even with the presence of a high conjugated core. The fluorescence quantum yields observed varied from low to moderate (Φ _F ?=?1–62%), with large Stokes shifts (60–178 nm). All compounds exhibited liquid crystalline behaviour with a wide mesomorphism temperature range and characteristic phases of calamitic compounds, among them smectic A (SmA), smectic C (SmC) and nematic (N) phases. Their phases were characterised using polarising optical microscopy and differential scanning calorimetry. In addition, with X-ray diffraction experiments, layer spacing of 33.3–40.0 Å were observed for the smectic phases.     

Enhanced wavelength-sensitivity of volume holographic grating with dual-photoinitiation system in polymer-dispersed liquid crystal

We propose a method to improve the wavelength-sensitivity of a volume holographic grating by mixing dual-photoinitiation dopants, namely, rose bengal (RB)/N-phenylglycine (NPG) system and methylene blue (MB)/p-toluenesulfonic acid (PTSA) system, which enable the fabrication of gratings upon both green and red light illumination. The RB/NPG green light photoinitiation system is chosen in combination with the red-active MB/PTSA system because RB and MB absorb light near 567 and 665 nm independently. In this case, the holographic gratings, recorded in polymer-dispersed liquid crystal, can be fabricated simultaneously by two different visible laser lights with an output wavelength of 532 and 632.8 nm. The electro-optical performances of the gratings exposed upon 532 and 632.8 nm have been implemented: the diffraction efficiencies (DE) are 75% and 57% respectively when the exposure time is optimised to 2 min and 17 min; the threshold voltage is approximately 2.9 V/μm. The enhanced wavelength-sensitivity of holographic gratings allows for the storage of three-dimensional (3D) images on the same hologram plate, and these 3D images are easily reconstructed by both red and green light.     

Synthesis and characterization of polymerizable photochromic liquid crystals containing a spiro-oxazine group

Novel polymerizable photochromic liquid crystal materials containing either the 1,3-dihydro-1,3,3-trimethylspiro[2H-indole-2,3'-[3H]naphth[2,1-b][1,4]oxazine] group or the 1,3-dihydro-1,3,3-trimethylspiro[2H-indole-2,3'-[3H]pyrido[3,2-f][1,4]benzoxazine] group as the photochromic moiety, and the biphenylene unit as the mesogenic moiety, were synthesized. Thermal and physical properties of the compounds were examined using differential scanning calorimetry, optical polarizing microscopy, wide-angle X-ray diffractometry and UV-visible spectrophotometry. The photochromic compounds containing both photochromic and mesogenic moieties showed metastable mesophases; These tended to crystallize with time and on heating. The crystallization behaviours were strongly dependent on the structure of the terminal group of alkylene spacer and the position of the spiro-oxazine bound to the mesogen.     

Segmented liquid crystalline polyesters with allyl group as lateral substituent

The synthesis and a partial characterization of segmented liquid crystalline polymers with 3,3′-diallyl-4,4′-dihydroxybiphenyl unit in the rigid moiety is reported. The general formula of polymers is [-p-C₆H₄-COO-p-C₆H₃(R)-p-C₆H₃(R)-OOC-p-C₆H₄-O-(CH₂)_nO-]_x, with n = 6, 8, 10, 12, and R =  CH₂ CHCH₂. All polymers have nematic liquid-crystalline behavior. At room temperature, annealed fiber samples of polymers show a complex polymorphism. Three phases have been isolated with very large unit cells accommodating 6 or 12 chains. The projection of the molecular packing in a plane perpendicular to the c axis is characterized by the organization of chains in a two-dimensional hexagonal or quasi-hexagonal array. © 1998 John Wiley & Sons, Inc. J. Polym. Sci. B Polym. Phys. 36: 2371–2378, 1998     

Functional Janus dendrimers containing carbazole with liquid crystalline,optical and electrochemical properties

ABSTRACT

Novel liquid crystalline Janus dendrimers that combine a mesogenic block and an electroactive block have been synthesised. The mesogenic block is based on two third-generation Percec-type dendrons bearing six or eight terminal dodecyloxy alkyl chains, whereas the electroactive blocks are formed by one or two carbazole units. The liquid crystal behaviour was investigated by polarised-light optical microscopy, differential scanning microscopy and X-ray diffraction. The Janus dendrimers with one electroactive unit exhibited cubic or columnar liquid crystal phases, whereas the Janus dendrimers with two electroactive units did not show liquid crystalline behaviour. The UV-vis absorption and emission properties of the Janus dendrimers were investigated. The spectra suggested the existence of π-π stacking and the formation of aggregates in the solid state. Electrodeposition of the carbazole-containing dendrimers afforded semi-globular particles in which the number of electropolymerizable units and the flexible or rigid character of the linker have a decisive influence in the particle size.     

Synthesis and properties of phenyl benzoate-based and biphenyl-based liquid crystalline thiol-ene monomers

Novel phenyl benzoate-based and biphenyl-based liquid crystalline thiol-ene monomers were synthesized and their properties investigated. By varying the bridging unit and spacer length, the type of mesophase can be tuned from the low ordered nematic and smectic A phase in the case of the phenyl benzoate-based monomers, to the highly ordered crystal E phase for the biphenyl-based monomers and their corresponding bromo precursors. We investigated the degree of order of the phenyl benzoate-based materials using the Haller method. Possible premature polymerization of these monomers was examined by size exclusion chromatography. The materials exhibit low transition temperatures and a high stability at typical handling times and temperatures. Consequently, these monomers are useful for in situ polymerization with anisotropic inert solvents, which could potentially lead to new architectures and enhanced electro-optical properties of devices. The use of the biphenyl-based monomers appears to be of limited use for polymerizations in anisotropic solution. However, as a result of their intrinsic high degree of molecular order, these monomers form a particularly interesting class of reactive materials that can be bulk polymerized to give main chain polymers with highly defined mechanical and optical or electro-optical properties.     

Polymerizable hexacatenar liquid crystals containing a luminescent oligo(p-phenylenevinylene) core

Polymerizable hexacatenar mesogens containing a photo-active oligo(p-phenylenevinylene) core were successfully synthesized by replacing the traditional n-alkoxy tails on the molecules with polymerizable hydrocarbon tails containing terminal isoprenyl or 1,3-dienyl units. It was found that for this particular liquid crystal (LC) platform, the incorporation of conventional radical polymerizable groups such as acrylates in the tails was not conducive to the formation of thermotropic LC phases, presumably due to their polar nature. The resulting photoluminescent isoprenyl and 1,3-dienyl hexacatenar monomers were found to form columnar hexagonal phases at elevated temperatures (c. 45–75°C), as determined by powder X-ray diffraction. Unfortunately, photoinitiated radical polymerization studies revealed that the mesogens are susceptible to photodegradation in the LC state at elevated temperatures, resulting in the loss of both LC order and emission properties during photopolymerization. Thermally initiated radical polymerization in the absence of light, however, afforded effective crosslinking with retention of both LC order and the desired emission properties. The resulting crosslinked columnar hexagonal phases were found to exhibit emission maxima at nearly identical wavelengths, with comparable intensities relative to the unpolymerized starting materials. The effect of the different polymerizable groups on the mesogenic behaviour, polymerization characteristics, and emission properties of the hexacatenar compounds is presented.     

Synthesis and characterisation of main-chain hydrogen-bonded supramolecular liquid crystalline complexes formed by azo-containing compounds

A series of azopyridine-containing hydrogen bonding acceptors (4a-c) with flexible spacers of oligo(methylene) were synthesised. Hydrogen-bonded polymeric complexes 4/5 and trimeric complexes 4/6₂ , where 5 and 6 are aromatic dicarboxylic acids and monocarboxylic acids, respectively, were prepared and their liquid crystallinity was examined using differential scanning calorimetry and polarising optical microscopy. The study showed that most of the complexes displayed reversible thermotropic nematic phase. The isotropic to nematic phase transition temperatures of polymeric complexes 4/5 and trimeric complexes 4/6₂ in general decreased with the increase in length of spacers and terminal groups in the corresponding proton acceptors 4 and the proton donors 5 and 6, respectively. Hydrogen bonding interactions in complexes 4/5 and 4/6₂ were studied by X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy.     

Supramolecular hexagonal structure of a segmented liquid crystalline polyester with allyl group as lateral substituent

The molecular structure of the phase—stable at room temperature—for the polymer with formula [ p C₆H₄ COO p C₆H₃(R) p C₆H₃(R) OOC p C₆H₄ O (CH₂)₁₀O ]_x, with R =  CH₂ CHCH₂, is reported. The cell is hexagonal (a = b = 13.43 Å, c = 33.3 Å, γ = 120°), space group P6₃, six chains per unit cell (d_calcd = 1.23 g cm⁻³). The six chains are packed together to give a bundle with the center of mass set at the origin of the unit cell. The allyl groups are placed inside the bundle, thus explaining the unexpected reactivity of the double bonds to give crosslinking when fiber samples are annealed in the solid state. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 1601–1607, 1999     

对二氨基二苯型芳酰胺类液晶化合物的合成与表征

液晶作为新型材料,在高新技术领域显示出越来越广阔的应用前景,目前科学界对各种类型的液晶,包括主链型,侧链型液晶以及热固性液晶方面的研究非常活跃~([1-4]).含有端烯类双键的液晶化合物,可以通过双键联结到高分子链上,形成高分子液晶化合物,也可与其它烯类单体发生共聚合反应,制备液晶热固性树脂,还可以通过双键氧化,制备液晶环氧树脂,因此有广泛的应用前景~([5,6]).