Mesomorphic Phase Transitions Research Articles

Dynamic change of molecular conformation generating a variation of liquid crystalline phases for triphenylene mesogens with peripheral alkoxyazobenzenes

ABSTRACT A triphenylene mesogen which possesses six dodecyloxyazobenzene units at the periphery linked by propylene-ether chain (2-C12-3) was synthesised and its mesomorphic phase transition behaviour was investigated. It was found that 2-C12-3 exhibits six mesophases including one monotropic phase. The calamitic-discotic bi-mesomorphic phase transition was also observed. As cooling the compound at the temperature of iso phase, SmA phase comes up and further cooling gives Col ob phase. In comparison to the corresponding ester-linked derivative (1-C12-3), which shows only two mesophases (SmA and Colr), the linkage part connecting triphenylene unit and the peripheral alkoxyazobenzenes significantly affect the molecular ordering in mesophase, though the bi-mesomorphic property is maintained in the case of dedecyloxy chains.

Liquid Crystalline Properties of 4,4and#39;-methylenebis(N-(4-Alkanoxybenzylidene)aniline): Synthesis, Characterization, and Theoretical study

The paper presents six homologues series of Schiff bases ether compounds distinguished by the length of terminal alkoxy groups which substituted on a side benzene nucleus. The above structures were demonstrated through the use of spectroscopic techniques, like FT- IR and 1H-NMR. Polarized hot stage optical microscopy was used to study both mesomorphic properties and phase transitions. The results showed that out of the six compounds only three (B2, B3 and B4) were pure (marble) nematic mesophase, while no liquid crystal properties for (B5, B6 and B7) compounds. The theoretical study for the electronic structures was intended to study the effects of alkyl chain length on the electronic structure by using Gaussian program, DFT and 6-31G as basis set. The theoretical results indicate that there is no effect to the terminal substituted alkoxy groups on the HOMO energies but there is an effect on LUMO energies through decreasing energy for the prepared compounds.

Luminescent fluorinated chiral liquid crystalline oligomers containing Eu(III) complexes

ABSTRACTLuminescent fluorinated chiral liquid crystalline oligomers containing Eu(III) complexes (Eu-LCOs) with good liquid crystalline properties and obvious luminescence properties were prepared using Poly(methylhydrogeno)siloxane (PMHS), chiral liquid crystalline monomer (M1), fluorinated liquid crystalline monomer (M2), fluorinated Eu(III) complex (M3). The chemical structures, liquid crystalline behaviours of Eu-LCOs were characterised by various experimental techniques. The introduction of small quantity of fluorinated Eu(III) complexes endowed the oligomers with excellent luminescence properties. The Eu(III) complexes did not change the liquid crystalline textures of the oligomers. Fourier transform infrared imaging showed that Eu(III) complexes were evenly distributed in oligomers. In order to express the mutual effect and distribution of the components, a structural representation of Eu-LCOs was established. The Eu-LCOs displayed wide mesophase temperature ranges and reversible mesomorphic phase transitions. The Eu-LCOs can emit soft red light when being excited. Luminescence intensities of Eu-LCOs gradually increased with an increase of Eu(III) complexes from 0 to 1.0 mol%. However, the luminescence intensities of Eu-LCOs decreased monotonically with the increase of temperature in liquid crystalline phase.

Mesomorphic phase transitions of 3F7HPhF studied by complementary methods

ABSTRACTPhysical properties and the phase sequence of (S)-4′-(1-methylheptyloxycarbonyl)biphenyl-4-yl 4-[7-(2,2,3,3,4,4,4-heptafluorobutoxy) heptyl-1-oxy]-2-fluorobenzoate exhibiting the liquid crystalline paraelectric smectic A*, ferroelectric smectic C* and antiferroelectric smectic CA* phases were studied by complementary methods in the temperature range from −125 to 120 °C. Differential scanning calorimetry measurements together with polarizing optical microscopy provided the phase sequence, including the glass transition and a cold crystallization. X-ray diffraction was used to obtain the unit-cell parameters of the crystal phase, as well as the layer thickness and correlation length in the liquid crystalline smectic phases. The tilt angle was found to reach 45°, as determined from the measurements of the layer thickness and molecular modeling. Relaxation processes in the smectic phases and the fragility parameter were studied using frequency-domain dielectric spectroscopy.

Luminescent Iridium-containing liquid crystalline polymers in the side chain

ABSTRACTLuminescent liquid crystalline polymers consisting of Iridium attached to polysiloxanes are prepared. 4-Cyanophenyl 4-(allyloxy) benzoate (M1) and an Iridium complex (Ir-M2) grafted to poly(methylhydrogeno)siloxane are used for the preparation of the Iridium-containing liquid crystalline polymers. The chemical structures are characterised by Fourier transform infrared spectroscopy and 1H NMR. The mesomorphic properties and phase behaviour are investigated by differential scanning calorimetry, thermogravimetric analysis, polarising optical microscopy and X-ray diffraction. The polymers containing <1.2 mol% of the Iridium ions reveal reversible mesomorphic phase transition, wide mesophase temperature ranges and high thermal stability. The introduction of the Iridium ions does not change the liquid crystalline state of polymer systems; on the contrary, the polymers are enabled with the luminescent properties. With the Iridium ion contents ranging between 0.3 and 1.2 mol%, luminescent intensity of polymers gradually increased. The temperature dependence of luminescent intensity was studied in the liquid crystalline phase.

Methimazolium-based ionic liquid crystals: Emergence of mesomorphic properties via a sulfur motif

We describe the proficient synthesis and thermotropic mesomorphicity of thioether–functionalized imidazolium–type ionic liquids containing C12 and C18 chains associated with Br− and OTf− anions. The mesomorphic behavior and phase transition temperatures were studied by Polarizing Optical Microscopy (POM), Differential Scanning Calorimetry (DSC) and Small-Angle X-ray Scattering (SAXS). The ionic liquids with bromide anion display Smectic A lamellar phase giving homeotropic and fan-shaped textures. The layered crystallographic structure is reported by Single-Crystal XRD. The electrochemical characteristics of the ionic liquids with C18 side chain have been determined via Cyclic Voltammetry.

2B05 長鎖末端にカルボン酸を有するトリフェニレン液晶における水素結合相互作用の変化と相転移挙動(化学・材料)

2B05 長鎖末端にカルボン酸を有するトリフェニレン液晶における水素結合相互作用の変化と相転移挙動(化学・材料)

Effect of alkyl chain length in the terminal ester group on mesomorphic properties of new chiral lactic acid derivatives

ABSTRACTTwo series of new liquid crystalline lactic acid derivatives with a terminal ester group have been synthesised. The effect of this ester unit and the length of its alkyl chain on the mesomorphic and dielectric properties of the compounds exhibiting a broad temperature range of chiral smectic phases have been studied. We found that the mesomorphic behaviour and phase transition temperatures are strongly affected by the molecular architecture. Depending on the alkyl chain length in the terminal ester unit, the studied materials exhibited paraelectric smectic A*, ferroelectric tilted smectic C* and antiferroelectric smectic CA* phases over a broad temperature range. The physical properties of the compounds have been studied by optical polarising microscopy, differential scanning calorimetry, electro-optic measurements, small-angle X-ray scattering and dielectric spectroscopy. Furthermore, the homologues with short terminal alkyl chains showed a very small layer shrinkage at the transition from the orthogonal SmA* to the tilted SmC* phase, which is a characteristic feature of ‘de Vries-type’ behaviour.

Novel fluorescent main-chain liquid crystalline ionomers containing Eu(III) ions

ABSTRACTNovel nematic fluorescent main-chain liquid crystalline ionomers containing Eu(III) ions (Eu-LCI) were synthesised by the use of bis(4-(chlorocarbonyl)phenyl) decanedioate (BD), 4,4-dihydroxybiphenyl (D), 2,5-dihydroxybenzoic acid (B) and anhydrous europium chloride. The chemical structures, liquid crystalline behaviours and fluorescence properties of Eu-LCI were characterised by various experimental techniques. The introduction of small amounts of europium ions endowed the LCI with excellent luminescence properties. POM results showed that europium ions did not change the liquid crystalline texture of the LCI. Fourier transform infrared imaging showed that europium ions were evenly distributed in the matrices of ionomers. A schematic diagram of nematic fluorescent LCI was established to demonstrate the interaction and distribution of the components. Eu-LCI showed reversible mesomorphic phase transitions, wide mesophase temperature ranges and high thermal stability. The thermogravimetric analysis (TGA) results showed that decomposition temperatures (5% weight loss) were greater than 308°C in all Eu-LCI. Eu-LCI can emit red light when excited. The luminescence intensity of Eu-LCI gradually increased with increase in Eu(III) ions from 0.3 to 1.5 mol%. The temperature dependence of luminescent intensity was studied in the liquid crystalline phase, where the fluorescence intensity of Eu-LCI decreased monotonically with increase in temperature.

Lyotropic model membrane structures of hydrated DPPC: DSC and small-angle X-ray scattering studies of phase transitions in the presence of membranotropic agents

Multibilayer structures of hydrated phospholipids, often considered as model biological membranes, are, from the physical viewpoint, lyotropic liquid crystalline systems undergoing temperature-induced mesomorphic phase transitions. Effects of silver nitrate and urocanic acid on lyotropic phase states of hydrated L-α-dipalmitoylphosphatidylcholine (DPPC) have been studied by small-angle X-ray scattering and differential scanning calorimetry (DSC). Both methods show increase of the main phase-transition temperature (Tm) of hydrated DPPC upon introduction of AgNO3 or urocanic acid, decrease of pre-transition temperature (Tp) in the presence of urocanic acid and its increase in the presence of AgNO3. Thus, urocanic acid widened the ripple-phase temperature region. Silver nitrate caused the appearance of an additional high-temperature peak on DSC thermograms, evidencing phase separation in the system. Both agents caused minor effects on DPPC lipid bilayer repeat distance (D) in gel phase, but resulted in noticeable increase of D in the liquid crystal phase with temperature as compared to undoped DPPC structures.

Mesomorphic and luminescence properties of side chain cholesteric liquid crystalline polymers containing Eu(III) and Tb(III) ions

Luminescent cholesteric liquid crystalline polymers consisting of the lanthanide ions covalently attached to cholesteric polysiloxanes are prepared. Cholesteric liquid crystalline monomer and 4-(allyloxy)benzoic acid grafted to poly(methylhydrogeno)siloxane is used as one of the precursors for the preparation of the lanthanide-containing cholesteric liquid crystalline polymers. The chemical structures of the monomers are characterised by Fourier transform infrared, 1H NMR and elemental analyses. The mesomorphic properties and phase behaviour are investigated by differential scanning calorimetry, thermogravimetric analysis, polarising optical microscopy and X-ray diffraction. The polymers containing <3 mol% of the lanthanide ions reveal reversible mesomorphic phase transition, wide mesophase temperature ranges and high thermal stability. The introductions of the lanthanide ions do not change the liquid crystalline state of polymer systems; on the contrary, the polymers are enabled with the significant luminescent properties. With the lanthanide ions contents ranging between 1 and 3 mol%, luminescent intensity and luminescent lifetimes of polymers gradually increased. The temperature dependence of luminescent intensity was studied in the liquid crystalline phase.

Luminescent lanthanide-containing chiral liquid crystalline polymers in the side chain

Luminescent lanthanide-containing chiral liquid crystalline polymers are graft-copolymerised using poly(methylhydrogeno)siloxane (PMHS), crosslinking agent, liquid crystalline monomer and lanthanide complexes. The chemical structures of the monomers are characterised by FTIR, 1 H NMR and elemental analyses. The mesomorphic properties and phase behaviour are investigated by differential scanning calorimetry, thermogravimetric analysis, polarising optical microscopy and X-ray diffraction. The polymers containing less than 9 mol% of the crosslinking units reveal reversible mesomorphic phase transition, wide mesophase temperature ranges and high thermal stability. With the introduction of lanthanide complex units, the polymers are enabled with the significant luminescent properties. The temperature dependence of fluorescence intensity was studied in the liquid crystalline phase. The IR imaging shows that the lanthanide complex units evenly distribute in polymers.

Synthesis and structure of lateral halogenated V-shaped liquid crystal molecules based on a 1,7-naphthalene central core and alkylthio tails

A series of small angle bent-core (V-shaped) mesogens carrying 1,7-naphthalene as a central core linked with lateral halogenated (chlorinated or fluorinated) Schiff-base side wings and alkylthio terminal tails of variable carbon number (n = 12, 16) was synthesised in order to reduce the transition temperature and improve the phase stability of bent-core liquid crystal molecules. Differential scanning calorimetry (DSC), polarising optical microscopy (POM), small-angle X-ray scattering system (SAXS) and two-dimensional X-ray diffractometer were applied to ascertain the mesomorphic structure and phase transition temperatures of the compounds. The results confirm that all the molecules show thermotropic liquid crystalline behaviour and exhibit hexagonal columnar phase (Colh) in a certain temperature range. Compared with the homologous compounds without lateral halogen, the cleaning point temperature of lateral halogenated V-shaped compounds generally decrease and the Colh phase ranges are more extensive. The influence of lateral chlorine on the cleaning point temperature is more obvious, as well as the effect of lateral fluorine on the range of Colh phase.

Mesomorphic thermal stabilities in supramolecular liquid crystals: Influence of the size and position of a substituent

A new homologous series of supramolecular Hydrogen Bonded Liquid Crystalline (HBLC) materials are synthesized with two low molar mass non-mesogenic moieties. The non-mesogenic substituted benzoic acids viz., 2-fluorobenzoic acid (2FBA), 3-fluorobenzoic acid (3FBA) and 4-fluorobenzoic acids (4FBA) are used as the proton donors. Non-mesogenic proton acceptors, PyBnA viz., (4-pyridyl)-benzylidene-4′-n-alkyl anilines (decyl, tetradecyl and hexadecyl) are used for the formation of supramolecular structures with the above proton donors. The HB between the two moieties is confirmed by FTIR spectroscopy. All the complexes exhibiting the smectic mesomorphism are characterized by Polarizing Optical Microscope (POM) equipped with a hot stage. Differential Scanning Calorimeter (DSC) is used to determine the enthalpy change across the mesomorphic phase transitions. The effect of position of fluorine atom and the chain length of proton acceptor on the mesomorphic stability is studied. The mesomorphic thermal stabilities and their melting/clearing temperatures are discussed in the wake of the data available on other supramolecular HBLCs with and without electronegative substituents on the proton donor moieties.

Synthesis of a liquid-crystalline resin monomer with the property of low shrinkage polymerization

To reduce the polymerization shrinkage of the dental resin composites, a new liquid-crystalline resin monomer was developed. The acrylate liquid crystalline resin monomer (ALCRM), (4-3-(acryloyloxy)-2-hydroxypropoxy) phenyl 4-(3-(acryloyloxy)-2-hydroxypropoxy) benzoate, was synthesized by a three-step method. Using the ALCRM as the main monomer, the degree of conversion (DC) and the volume shrinkage of the resin matrix were compared with the traditional composite resin monomer (Bis-GMA), 2,2-bis[4-(2-hydroxy-3-methacryloyloxy-propoxy)-phenyl] propane. The new monomer showed liquid crystalline characteristics with a mesomorphic phasetransition temperature between 18ºC and 42ºC. When copolymerized with triethylene glycol dimethacrylate (TEGDMA) at a weight ratio of 7:3, the DC of ALCRM was higher and the volume shrinkage was 3.62±0.26%, which was less than that of the Bis-GMA. The ALCRM exhibits promising potential for the development of superior dental resins with low volume shrinkage.

Thermotropic poly(azomethine-urethane)s with non linear optical properties: Synthesis and characterization

Two series of the thermotropic main chain poly(azomethine-urethane)s were synthesized by the polyaddition of azadiol, 1,8-octandiol with methylene bis(phenyl isocyanate) (MDI) and tolylene 2,4-diisocyanate (TDI) respectively. The mesomorphic properties and phase transition temperature of the polymers were characterized by differential scanning calorimetry and hot stage polarizing microscopy. These polymers showed nematic messophase. The non linear optical (NLO) activity of the polymers was also investigated.

Mesomorphic Properties of an Homologous Series of Thioalkyl-Terminated Azomesogens

A new homologous series (ten compounds) of 2-hydroxy azo compounds SRn (where n:1–10) were synthesized. Their structures were elucidated using spectroscopic techniques such as IR (Infrared), 1H-NMR as well as elemental analysis. Mesomorphic properties and phase transitions were studied using polarized hot stage optical microscopy and differential scanning calorimetry (DSC), and are discussed as a function of the number of carbon atoms in the thioalkyl chain. It has been found that all compounds in the series are pure nematogens.

Pendant triazole ring assisted mesogen containing side chain liquid crystalline polymethacrylates: Synthesis and characterization

Two series of click chemistry assisted alkoxymethyl-1H-[1,2,3]-triazol-1-yl containing side-chain liquid-crystalline polymethacrylates were synthesized by free radical polymerization technique. Mesogen was linked to backbone through various spacer units. Monomers and polymers were characterized by FT-IR, 1H and 13C-NMR spectral techniques. Thermal stability of polymers was confirmed by thermogravimetric analysis. Mesomorphic property and phase transition temperature of polymers were analysed by differential scanning calorimetry and polarized optical microscopy. Phase transition temperature and mesomorphic property of polymers with respect to insertion of polar alkoxy group on terminal triazole ring and spacer length between backbone and mesogen were investigated. Polymers exhibited grainy like textures under polarized optical microscopy. Spacer length between mesogen and backbone alters phase transition temperature of the polymers. Two series of click chemistry assisted alkoxymethyl-1H-[1, 2, 3]-triazol-1-yl containing side-chain liquid-crystalline polymethacrylates were synthesized by free radical polymerization technique.

Structure and Properties of Phosphorous‐Containing Thermotropic Liquid‐Crystalline Aliphatic–Aromatic Copolyesters

AbstractA series of thermotropic liquid crystalline aliphatic–aromatic copolyesters derived from various ratios of dodecane‐1,12‐diol (1), terephthaloyl bis‐(4‐oxybenzoyl‐chloride) (2), and 2‐(6‐oxido‐6H‐dibenz〈c,e〉〈1,2〉 oxaphosphorin‐6‐yl)‐1,4‐naphthalene diol (3), has been synthesized. The chemical structures of the monomers and polymers have been confirmed by elemental analyses, and FT‐IR and1H NMR spectroscopy. The mesomorphic properties of polymers have been investigated by differential scanning calorimetry, polarizing optical microscopy, and X‐ray diffraction measurements. The influence of the content of the aliphatic unit on the phase behavior of the polymers has been examined. The polymers that contain &gt;30 mol‐% aliphatic diol showed smectic phases while the polymers that contained &lt;30 mol‐% aliphatic diol displayed nematic phases. The polymers revealed a reversible mesomorphic phase transition, wide mesophase temperature ranges, and high thermal stability. The degree of crystallinity increased upon increasing the content of aliphatic moieties. The char yield at high temperature increased by increasing the content of phosphorous‐containing bisphenol.magnified image

Mesomorphic phase transition behaviour of photopolymerisable liquid crystalline triphenylene ether compounds

This report discusses the preparation and the unusual mesomorphism of three homologues of photopolymerisable triphenylene ether compounds. These homologues showed ‘a cold crystallisation’ on heating differential scanning calorimetry curves, and this phenomenon is attenuated with increase methylene units, spacers between the triphenylene core and the terminal photopolymerisable acrylate group. Classical textures of hexagonal columnar (Colh) mesophase were observed by polarising optical microscopy for all three photopolymerisable mesophase compounds described here. Also described is the mesomorphism of their intermediates, hydroxylalkoxytriphenylenes. In some cases, the discotic columnar hexagonal mesophases were confirmed by wide angle X-ray scattering techniques.