The influence of structural changes of symmetrical dimers containing two phenyl groups on liquid crystalline behaviour

Some symmetrical dimeric compounds containing biphenyl, biphenylcarboxylic acid or benzoiloxyphenyl moieties and polymethylene spacers were synthesised. The mesogenic properties of the synthesised compounds were investigated by optical microscopy, calorimetric and X-ray methods. It was shown that the location and direction of the ester bonds has a crucial significance in mesophase formation.     

Liquid crystalline behaviour of hydrazide derivatives containing alkoxyazobenzene

Two series of dissymmetric hydrazide derivatives containing alkoxyazobenzene with nitro terminal group and octyloxy terminal group, N-4-alkoxyphenyl-N′-4-((4-nitrophenyl)azophenyl) benzohydrazide (Bn-NO₂, n indicates the number of carbon atoms) and N-4-octyloxyphenyl-N′-4-((4-octyloxyphenyl)azophenyl) benzohydrazide (B8-B8), were designed and synthesised, and their liquid crystalline properties were investigated by means of differential scanning calorimetry, polarised optical microscopy and wide-angle X-ray diffraction. It was found that B8-B8 with octyloxy terminal chains displayed monolayer smectic C phase, whereas Bn-NO₂ with nitro terminal group displayed SmA_d phase, and intermolecular hydrogen bonding was confirmed as the driving force. In addition, the effect of hydrogen bonding, dipole–dipole interactions and steric hindrance effect on the liquid crystalline structures were also discussed.     

Liquid crystalline behaviour of benzoic acid derivatives containing alkoxyazobenzene

Liquid crystal trimers based on the hydrogen bonding dimerization of 4‐{n‐[4‐(4‐m‐alkoxy‐phenylazo)phenoxy]alkoxy}benzoic acid (BAm‐n) have been synthesized and characterized. Temperature‐dependent FTIR spectroscopic studies showed that the carboxylic acid groups in BAm‐n are associated to form H‐bonded cyclic dimers both in their crystalline and liquid crystalline phases. The trimers exhibited enantiotropic liquid crystalline behaviour except for BA1‐3 which showed monotropic behaviour, and the mesophases changed from nematic to smectic phase, with the increase of length of the spacer and the terminal substituents. Pronounced odd–even effects in the melting temperatures, clearing temperatures and nematic–isotropic enthalpy changes were observed.     

Liquid crystalline behaviour of thienyl-enaminoketone derivatives containing halogen atoms

New homologous series containing a thienyl-enaminoketone-phenyl (TEP) core substituted by a halogen atom have been synthesized. It is shown that the stability of the orthogonal phases decreases with the decreasing electron-accepting properties of the halogen atom. Generally the materials studied form orthogonal smectic phases, but in additional, tilted smectic phases are observed in iodine-substituted series as well as for two homologues containing bromine in the thienyl ring. For comparison, a homologous series containing a terminal cyano group was also studied.     

Thermotropic main chain liquid crystalline polyesters containing ferrocene and phosphate units: synthesis and characterization

A new series of liquid crystalline main chain copolyesters were prepared, having ferrocene in the mesogenic segment and a methyl phosphate group along with a methylene spacer. The even numbered methylene groups were varied from two to ten. Liquid crystalline behaviour was investigated on a hot stage optical polarized microscope. Thermal properties of the polymers were analysed by TGA and DSC, revealing that the polymers yield high char products, probably caused by the formation of phosphorus and iron oxides. The glass transition (T_g) temperatures of the polymers were found to be fairly low, the result of the incorporation of bulky phosphorus and ferrocene moieties in the chain. The phase behaviour was analysed and correlated with the structure of the polymers. The liquid crystalline textures of the polymers became more transparent with increasing spacer length. Energy minimized structures for the polymer repeating units reveal that both the ferrocene and phosphorus moieties produce more molecular entanglement, thus reducing the T_g and T_m of the polymers.     

Thermotropic main chain liquid crystalline polyesters containing ferrocene and phosphate units: synthesis and characterization

A new series of liquid crystalline main chain copolyesters were prepared, having ferrocene in the mesogenic segment and a methyl phosphate group along with a methylene spacer. The even numbered methylene groups were varied from two to ten. Liquid crystalline behaviour was investigated on a hot stage optical polarized microscope. Thermal properties of the polymers were analysed by TGA and DSC, revealing that the polymers yield high char products, probably caused by the formation of phosphorus and iron oxides. The glass transition (T _g) temperatures of the polymers were found to be fairly low, the result of the incorporation of bulky phosphorus and ferrocene moieties in the chain. The phase behaviour was analysed and correlated with the structure of the polymers. The liquid crystalline textures of the polymers became more transparent with increasing spacer length. Energy minimized structures for the polymer repeating units reveal that both the ferrocene and phosphorus moieties produce more molecular entanglement, thus reducing the T _g and T _m of the polymers.     

The behaviour of some ferrocene derivatives under electron impact

The behaviour of some mono- and di-substituted ferrocene compounds under electron impact has been investigated by means of low-resolution mass spectrometry. Some characteristic rearrangement processes have been observed and discussed.     

Synthesis and crosslinking of a series of dimeric liquid‐crystalline diglycidylester compounds containing imine groups

We used readily available commercial reagents and well‐known procedures to synthesize a series of aromatic imine mesogenic diglycidylester compounds with dimeric architectures. The compounds obtained were characterized by spectroscopic techniques. Their liquid‐crystalline behavior was examined by differential scanning calorimetry, hot‐stage polarized optical microscopy (POM), and wide‐angle X‐ray scattering (WAXS) and related to the different structures that varied in the length of the central spacer. All the compounds exhibited nematic mesophases with the exception of the dimer with a three‐methylene central spacer that did not reveal liquid‐crystalline character. We investigated the crosslinking of the synthesized compounds and obtained liquid‐crystalline thermosets (LCTs) with several primary aromatic diamines in stoichiometric ratios or a tertiary amine as a catalyst. The curing processes were measured by calorimetry, and the thermal stability of the LCTs was evaluated by thermogravimetry. The ordered character of the LCTs was confirmed by POM and WAXS. Finally, the mechanical characterization of the LCTs obtained was examined by dynamic mechanical thermal analysis. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 4344–4356, 2002     

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.     

Synthesis and characterization of novel photoisomerizable liquid crystalline polymers containing cinnamoyl groups

A series of novel liquid crystalline monomers and polymers incorporating phenylbenzoate or phenylcinnamate segments as mesogenic cores have been synthesized to investigate the sensitivity of the photochromic cinnamoyl derivatives and to overcome the defects of the thermal instability of azobenzene. Their liquid crystalline, thermal, and photoinduced properties of all monomers and polymers were characterized. The polymers showed excellent solubility in common organic solvents such as CHCl₃, toluene, and DMF and exhibited good thermal stability with decomposition temperatures (T_d) at 5% weight loss greater than 340 °C and about 50% weight loss occurred beyond 430 °C under nitrogen atmosphere. The pitch length (about 574 nm) of the synthesized cholesteric polymeric film ( CP2 ) was estimated using scanning electron microscopy. These photochromic polymers exhibited strong UV–vis absorption maxima at about 264 or 320 nm. Moreover, photo induced configurational E/Z isomerization further changed the π‐electron conjugation systems leading to a decrease at the π‐π* transition and an increase in the range of 300 nm to 400 nm for photochromic copolymers. The thermal stability of the Z‐structural segment was confirmed by heating the polymer at 50 °C for over 5 h. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 1289–1304, 2008     

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.     

Liquid crystalline lonomers. I. Main-chain liquid crystalline polymer containing pendant sulfonate groups

Liquid crystalline polymers containing sodium sulfonate groups pendant to the polymer backbone were synthesized by an interfacial condensation reaction of brilliant yellow, a sulfonate-containing monomer, with 4,4′-dihydroxy-α,α′-dimethyl benzalazine and a 50/50 mixture of sebacoyl and dodecanedioyl dichlorides. Polymers containing up to ca. 4 mol% brilliant yellow were characterized by elemental analysis and ultraviolet spectroscopy. The polymers were thermally stable to about 300°C, and they exhibited a broad nematic mesophase region of 70–100°C. The solution viscosity behavior in chloroform suggested that intramolecular associations of the sulfonate groups occurred at low polymer concentrations and intermolecular associations predominated at higher concentrations.     

Structures, properties and miscibility behaviour of liquid crystalline polycatenar tetrone derivatives

The tetrones represent an interesting new mesogenic building block. The results of this study show that they can be incorporated into a variety of mesophases. A smectic phase was observed in the polycatenar compound with four terminal chains as expected. The phase exhibits a tilted structure (S_c phase) to prevent void formation. The compound with six pendant chains forms a columnar phase. In spite of their structural similarity, the tetrones studied tended not to be completely miscible. However, complete miscibility with a semi-discoid phenylhydrazone was observed. When this hydrazone, which forms a columnar 'D_ho phase', was mixed with tetrone which forms a columnar 'D_hd phase' a columnar hexagonal phase was produced with enhanced stability. We believe that the stability enhancement derives from a charge transfer interaction between the tetrone and the phenylhydrazone.     

Antiferroelectric phase in liquid crystalline compounds containing an azo group in their molecular core

Novel lactic acid derivatives containing an azo group in their molecular core have been synthesised and their mesomorphic properties established. Compounds with a short aliphatic non-chiral chain exhibited the SmA* phase and ferroelectric (FE) SmC* phase. The monotropic antiferroelectric (AF) phase was found in the homologues with a longer terminal chain. Spontaneous polarisation and tilt angle were measured for the FE and AF phases. Dielectric spectroscopy in the frequency range 1 Hz–10 MHz was carried out and dielectric properties established within the temperature range of the smectic phases. Two high frequency modes were detected in the AF phase. Small-angle X-ray measurements were conducted, and the temperature dependence of layer spacing values is established and discussed.     

Study on new chiral liquid crystalline monomers and polymers containing menthyl groups

A series of new chiral monomers (M1–M4) and the corresponding siloxane polymers (P1–P4) containing menthyl groups were synthesised to establish the relationship between their structure and liquid crystalline properties. The effect of the mesogenic core rigidity and the spacer length on the phase behaviour of the monomers and polymers obtained in this study was discussed. The selective reflection of light for the chiral monomers was studied with UV-Vis spectrometer. Polarising optical microscopy, differential scanning calorimetry, X-ray diffraction and thermogravimetric analysis were used to characterise the phase behaviour and thermal stabilities. It was found that these chiral monomers and polymers were beneficial for the formation of the mesophases when a flexible spacer was inserted between the mesogenic core and terminal menthyl groups. M1–M3 showed enantiotropic chiral smectic C phase and cholesteric phase, and monotropic cubic blue phase on cooling cycle. M4 only showed cholesteric phase. P1–P4 showed a smectic A phase. With increasing the mesogenic core rigidity or decreasing the spacer length, the corresponding melting temperatures, glass transition temperatures and isotropic temperatures all increased.     

Anion‐binding properties of two calix[4]arene derivatives containing two ferrocene imine or ferrocene amine units at the upper rim

Calix[4]arene derivatives containing ferrocene units at the upper rim have been synthesized and their anion‐binding and sensing investigated towards anions such as chloride, bromide and hydrogen sulfate by cyclic voltammetry. Electrochemical studies show that these redox‐active ligands electrochemically recognize chloride and bromide anions. These compounds have excellent selectivity for chloride and bromide ions, in the comparison with hydrogen sulfate anion. With ferrocenyl Schiff base calix[4]arene 1 an anodic shift as large as 302 mV is observed on addition of four equivalents of Cl⁻ anion. Also electrochemical and UV–vis spectroscopic titrations ferrocenyl calix[4]arene derivatives 1 with chloride and bromide ions and 2 (only with Cl⁻) indicate a 1:1 binding‐stiochiometry. Copyright © 2011 John Wiley & Sons, Ltd.     

Synthesis and thermal behaviour of liquid crystalline pyridinium bromides containing a biphenyl core

A range of new pyridinium bromides was synthesized by the quaternization of different substituted pyridines with a group containing a biphenyl core and alkyl chains of differing lengths. The phase behaviour of the pyridinium bromides was studied by differential scanning calorimetry, polarizing optical microscopy and powder X-ray diffraction. It is shown that pyridinium moieties, linked to a rod-like biphenyl core via an alkyl spacer, can form ionic liquid crystals. Unsubstituted pyridinium groups promote mesomorphism. Liquid crystalline phases are formed only from 2- and 4-ethyl substituted pyridinium groups with sufficiently long alkyl terminal chains and spacers; i.e. decyl chains on both sides of the biphenyl core. Both the substitution pattern at the pyridinium group and the alkyl chain length have an influence on the polymorphism of the smectic phases. 3,5-Dimethyl substitution hinders mesophase formation.     

Synthesis and thermal behaviour of liquid crystalline pyridinium bromides containing a biphenyl core

A range of new pyridinium bromides was synthesized by the quaternization of different substituted pyridines with a group containing a biphenyl core and alkyl chains of differing lengths. The phase behaviour of the pyridinium bromides was studied by differential scanning calorimetry, polarizing optical microscopy and powder X-ray diffraction. It is shown that pyridinium moieties, linked to a rod-like biphenyl core via an alkyl spacer, can form ionic liquid crystals. Unsubstituted pyridinium groups promote mesomorphism. Liquid crystalline phases are formed only from 2- and 4-ethyl substituted pyridinium groups with sufficiently long alkyl terminal chains and spacers; i.e. decyl chains on both sides of the biphenyl core. Both the substitution pattern at the pyridinium group and the alkyl chain length have an influence on the polymorphism of the smectic phases. 3,5-Dimethyl substitution hinders mesophase formation.