Thermotropic Liquid Crystalline Properties Research Articles

Thermotropic Colloidal Liquid‐Crystalline Hydroxyapatite Nanorod Hybrids Containing a Forklike Mesogen

AbstractWe here report the development of new thermotropic colloidal liquid‐crystalline (LC) organic/inorganic hybrids consisting of a hydroxyapatite (HAp)/poly(acrylic acid) (PAA) nanorod and a dendritic forklike mesogen. Complexation of the HAp/PAA nanorod covered with negatively charged PAA and a cationic forklike mesogen through electrostatic interactions and cation metathesis results in the surface modification of the HAp/PAA nanorod with the forklike mesogen. While the HAp/PAA nanorod forms a lyotropic colloidal LC phase in the aqueous dispersion, the HAp/PAA nanorod modified with the forklike mesogen exhibits thermotropic colloidal LC phases in the solvent‐free states. The biomineral‐based organic/inorganic colloidal liquid crystals exhibiting thermotropic LC properties have potential for the development of new stimuli‐responsive sustainable materials.

Color-tunable photoluminescent discotic liquid crystal based on perylene – Pentaalkynylbenzene triad

This article describes the design and development of a discotic triad, where perylene is sandwiched between two pentaalkynyl benzene units, linked via a flexible alkyl spacer. The thermotropic liquid crystalline properties of the compound were analyzed by differential scanning calorimetry (DSC), polarising optical microscopy (POM), and wide-angle X-ray diffraction (WXRD) techniques. The compound exhibits columnar oblique (Colob) mesophase that sustains over a significant temperature range. The corresponding electron density map was derived from the intensities observed in the diffraction pattern. The photophysical behaviour of the compound in various solvents of varying polarity has been studied. The compound shows positive solvatochromism with a significant increase in Stoke's shift of around 91 nm between toluene and ethanol. The compound shows high fluorescence quantum yield in non-polar solvents and the lowest in polar solvents. The presented luminescent material with positive solvatochromism will reveal its potential application in fluorescence imaging and the field of optoelectronic organic materials.

Synthesis of novel liquid crystal compound and study of its behavior as corrosion inhibitor for mild steel in acidic medium (1 M) HCl

Novel liquid crystal (LC) namely, (E)-N-hexadecyl-4-(((4-iodophenyl)imino)methyl)-N,N-dimethylbenzenaminium bromide (IC16) was prepared and characterized by Fourier transform infrared (FT-IR), 1H nuclear magnetic resonance spectra, and mass spectrometry. The thermotropic liquid-crystalline (LC) properties were examined by differential scanning calorimetry (DSC). The prepared LC was evaluated as corrosion inhibitor with non-electrochemical and electrochemical methods. Electrochemical methods include potentiodynamic polarization (PP), electrochemical impedance spectroscopy (EIS), electrochemical frequency modulation (EFM). Non electrochemical method measuring with different temperature. The results showed that the synthesized compound possesses liquid crystal properties and it has a significant efficiency as anticorrosion (91%–97%). The adsorption of IC16 compound on mild steel surface was found to follow the Langmuir isotherm.

Synthesis and thermotropic liquid-crystalline properties of a hexyloxy-substituted pyridyl-ethynylene-azobenzene and its halogen-bonded complex with tetrafluoroiodophenyl decanoate

This work deals with the synthesis and thermotropic behavior of a hexyloxy-substituted pyridyl-ethynylene-azobenzene and its halogen-bonded complex (XB complex) with tetrafluoroiodophenyl decanoate. The XB complex here reported is a highly anisotropic photoactive mesogen. It displays only smectic-type order where two different lamellar stacks seem to co-exist. The smectic period (determined by XRD) shorter than the theoretical length of the XB-complex suggests a single layer stacking of molecules, which may be arranged head-to-tail to satisfy the electrostatic interactions between fluorinated and non-fluorinated rings. Finally, photo-isomerization and NMR experiments seem indicate that the halogen-bonded complex is stable in solution.

Ionic liquid crystals: Synthesis and characterization via NMR, DSC, POM, X-ray diffraction and ionic conductivity of asymmetric viologen bistriflimide salts

A series of asymmetric viologen bistriflimide salts of both short and long alkyl chains were synthesized by the metathesis reaction of lithium triflimide salt with the respective asymmetric viologen dibromide salts in methanol. Their thermotropic liquid crystalline properties were determined by differential scanning calorimetry, polarizing optical microscopy and variable temperature X-ray diffraction techniques. These salts melt into highly-ordered smectic T phases that is, crystal-to SmT transitions (Tms) at relatively low temperatures (lowest Tm at −12 °C) and maintain liquid crystallinity in a wide range of temperatures (8–132 °C), with excellent thermal stabilities up to 320 °C as determined by thermogravimetric analysis. These results differ with respect to the symmetric viologen bistriflimide salts. Ionic conductivity of these salts was also measured by dielectric impedance spectroscopy and found to be in the 10−2.5 S cm−1 range, highlighting their potential as electrolytes at room temperature.

From cyclohexanone to photosensitive polyesters: Synthetic pathway, basic characterization, and photo-/halochromic properties

A bifunctional photosensitive monomer, 2,6-bis-(4-hydroxybenzylidene)cyclohexanone (DHCH) was successfully synthesized by the condensation reaction of cyclohexanone with p-hydroxybenzaldehyde in the presence of hydrochloric acid, as a catalyst. Based on DHCH, a series of new photosensitive polyesters were prepared by a polycondensation reaction, in solution, using two phosphonic dichlorides, namely, phenylphosphonic dichloride and phenyl dichlorophosphate, or two aromatic dichlorides, namely, terephthaloyl chloride and terephthaloyl-bis-(4-oxybenzoylchloride). The synthesis of monomer and polymers was structurally confirmed by FT-IR and NMR spectroscopies. The thermal behavior of polyesters was investigated by DSC measurements and polarized optical microscopy observations, which evidenced thermotropic liquid crystalline properties for some of the studied polymers. The photoresponsive properties of the prepared polyesters were extensively investigated in CHCl3 and DMSO solutions, under irradiation with UV light (254 and 365 nm) at different time intervals and after successive titrations with acid/base solutions. Under UV light irradiation, these compounds undergo photocrosslinking reactions and their photoluminescence properties were strongly enhanced. Deprotonation (under the basic conditions) of the polymers led to the emergence of a new absorption band (with maximum at 508 nm), accompanied by a photochromic behavior. This color change, from colorless to orange, observed upon titration with dilute NaOH solution, was completely recovered to its original colorless after the addition of an equivalent amount of dilute HCl solution. The reversible color changes (halochromic properties) observed upon protonation/deprotonation prove that these polymers have potential applications in chemical sensors.

Thermotropic Liquid-Crystalline and Light-Emitting Properties of Bis(4-aalkoxyphenyl) Viologen Bis(triflimide) Salts.

A series of bis(4-alkoxyphenyl) viologen bis(triflimide) salts with alkoxy chains of different lengths were synthesized by the metathesis reaction of respective bis(4-alkoxyphenyl) viologen dichloride salts, which were in turn prepared from the reaction of Zincke salt with the corresponding 4-n-alkoxyanilines, with lithium triflimide in methanol. Their chemical structures were characterized by 1H and 13C nuclear magnetic resonance spectra and elemental analysis. Their thermotropic liquid-crystalline (LC) properties were examined by differential scanning calorimetry, polarizing optical microscopy, and variable temperature X-ray diffraction. Salts with short length alkoxy chains had crystal-to-liquid transitions. Salts of intermediate length alkoxy chains showed both crystal-to-smectic A (SmA) transitions, Tms, and SmA-to-isotropic transitions, Tis. Those with longer length of alkoxy chains had relatively low Tms at which they formed the SmA phases that persisted up to the decomposition at high temperatures. As expected, all of them had excellent thermal stabilities in the temperature range of 330–370 °C. Their light-emitting properties in methanol were also included.

Two Novel π -Conjugated Fluorophores for Dye-Doped LC On-Off Photoluminescence Switching

Among various classes of Photoluminescent (PL) compounds, soft-matter based materials in which chromophores are embedded in a Liquid-Crystal (LC) host polymer prove to be very attractive in the production of flexible panels and on-off temperature switches. Actually, the obtainment of low cost, easily synthesizable, and stable organic molecules soluble in the LC matrix is a challenge for both scholars and technologists. Here we describe the synthesis of two new emissive dyes based on a dicyanophenylenevinylene and on a bis-azobenzene core whose PL properties were investigated as neat solids, in solution, and in particular in a dye-doped LC nematic polymer often employed in PDLC applications. 1H NMR and 13C NMR spectroscopy allow the characterization of all compounds Their thermotropic liquid- crystalline (LC) properties were examined by differential scanning calorimetry and polarizing optical microscopy. Photoluminescence properties were characterized by fluorescence spectra.

A liquid-crystalline semiconducting polymer based on thienylene–vinylene–thienylene: Enhanced hole mobilities by mesomorphic molecular ordering and thermoplastic shape-deformable characteristics

Liquid-crystalline (LC) π-conjugated polymers are an emerging class of semiconducting materials owing to their promising performance in organic field-effect transistors (OFETs). Little is known, however, about the relationship between LC nature and charge carrier mobility. In this paper, we focus on a thiophene-based p-type semiconducting polymer, PC12TV12T, containing thienylene–vinylene–thienylene (TVT) units, and report a systematic investigation of its thermotropic LC properties, self-organized structures in bulk and thin films, as well as charge transport properties in OFETs. We found that thermal annealing at LC temperatures (99–170 °C) strongly enhanced OFET performance, leading to field-effect hole mobilities as high as 0.37 cm2 V−1 s−1, comparable to that of amorphous silicon. By virtue of its thermoplasticity, the TVT-based polymer can also be processed into fine semiconducting microfibers, which can even function as a p-type active channel for charge transport. This bottom-up technology utilizing the LC nature enables cost-effective and energy-efficient manufacture of optoelectronic devices. A π-conjugated polymer based on thienylene–vinylene–thienylene (TVT) units can form a thermotropic liquid-crystalline (LC) mesophase over a wide temperature range. Thermal annealing at LC temperatures strongly enhanced hole mobilities in organic field-effect transistors (OFETs) owing to improved molecular ordering. Because of its thermoplasticity, the TVT-based π-conjugated polymer can also be processed into semiconducting fine microfibers and serve as a charge transport pathway in microfiber OFETs.

Cytotoxic Anti-Cancer Activity of Certain Thermotropic Liquid Crystalline Poly (Ester-Amides) Containing 2, 6-Bis (Benzylidene)Cyclohexanone Moiety in the Main Chain

Five thermotropic liquid crystalline poly(ester-amides) were synthesized by polycondensation method. The poly(ester-amides) were synthesized from varying dicarboxylic acids with a common diamine namely 4,4'-diaminobenzene and a common diol namely 2,6-bis(4-hydroxybenzylidene))cyclohexanone. For qualitative characterization, viscosity measurements and solubility data were used for these synthesized poly(ester-amides). The spectroscopic techniques such as FT-IR, 1H NMR, 13C NMR were performed to investigate the microstructural features of these synthesized poly(ester-amides). The thermal phase transition behavior of these poly(ester-amides) were studied by Differential Scanning Calorimetry (DSC) and Hot-stage Optical Polarized Microscopy (HOPM). The degree of crystallinity was assessed by X-ray diffraction (XRD) patterns. Scanning Electron Microscopic (SEM) technique was used to illustrate the morphology of these poly(ester-amides). The copolymer synthesized was subjected into in vitro anti-cancer activity studies against human breast cancer (MCF-7) cell line.
 Keywords: Bisbenzylidenecyclohexanone; poly(ester-amides); polycondensation; thermotropic liquid crystalline properties; cytotoxicity, anticancer.

Magnetic Gemini Surfactants.

A homologous series of Gemini surfactants, dimethylene-1,2-bis(alkyldimethyl-ammonium bromide) (referred to as n-2-n·2Br, n = 14, 16, and 18) and Fe- or lanthanide metal-based magnetic Gemini surfactants (abbreviated as n-2-n·2X, X = Fe, Ce, and Gd), were first synthesized. Measurements of surface tension and electrical conductivity determine the physical quantities related to the surface activities of n-2-n·2Br and n-2-n·2X, and the magnetic behaviors of n-2-n·2X are elucidated by superconducting quantum interference device magnetometry. Thermogravimetric analysis and differential scanning calorimetry have been used to investigate thermotropic liquid crystalline properties of all aforementioned surfactants, and the liquid crystal textures were further observed via polarizing optical microscopy. These results reveal that for magneto-responsive Gemini surfactants, both magnetic counterions and alkyl chain lengths have certain effect on surface activities, magnetism, and thermotropic phase behavior. We summed up these changes and discussed the causes, which could provide a new insight into controlling the properties of magnetic surfactants.

Supramolecular Arene-Ruthenium Metallacycle with Thermotropic Liquid-Crystalline Properties

Functionalization of 1,4-di(4-pyridinyl)benzene with poly(arylester) dendrimers bearing cyanobiphenyl end-groups gives a bidentate dendromesogenic ligand (L) that exhibits thermotropic liquid-crystalline properties. Combination of the diruthenium complex [Ru2(p-cymene)2(donq)][DDS]2 (M) with L, by coordination-driven self-assembly, affords the discrete and well-defined metallacycle M2L2. Like L, this supramolecular dendritic system displays mesomorphic properties above 50 °C. Both compounds L and M2L2 show smectic phases, characterized by a multilayered organization of the multiple components.

Thermotropic Liquid-Crystalline and Light-Emitting Properties of Poly(pyridinium) Salts Containing Various Diamine Connectors and Hydrophilic Macrocounterions.

A set of poly(pyridinium) salts containing various diamine moieties, as molecular connectors, and poly(ethyleneglycol)-4-nonylphenyl-3-sulfopropyl ether, thereafter referred to as “Macroion”, as the hydrophilic counterion, were prepared by metathesis reaction from the respective precursory tosylated poly(pyridinium)s in methanol. The structure of these ionic polymers was established by spectroscopy and chromatography techniques. The shape-persistent ionic poly(pyridinium) materials, inserting rigid or semi-rigid diamine spacers, display thermotropic liquid-crystalline properties from room-temperature up to their isotropization (in the temperature range around 160–200 °C). The nature of the LC phases is lamellar in both cases as identified by the combination of various complementary experimental techniques including DSC, POM and variable-temperature SAXS. The other polymers, inserting bulky or flexible spacers, only form room temperature viscous liquids. These new macromolecular systems can then be referred to as polymeric ionic liquid crystals (PILCs) and or polymeric ionic liquids (PILs). All the ionic polymers show excellent thermal stability, in the 260–330 °C temperature range as determined by TGA measurements, and a good solubility in common organic solvents as well as in water. Their optical properties were characterized in both solution and solid states by UV−Vis and photoluminescent spectroscopies. They emit blue or green light in both the states and exhibit a positive solvatochromic effect.

Thermotropic Liquid-Crystalline Properties of Viologens Containing 4-n-alkylbenzenesulfonates

A series of viologens containing 4-n-alkylbenzenesulfonates were synthesized by the metathesis reaction of 4-n-alkylbenzenesulfonic acids or sodium 4-n-alkylbezenesulfonates with the respective viologen dibromide in alcohols. Their chemical structures were characterized by Fourier Transform Infrared, 1H and 13C Nuclear Magnetic Resonance spectra and elemental analysis. Their thermotropic liquid-crystalline (LC) properties were examined by differential scanning calorimetry and polarizing optical microscopy. They formed LC phases above their melting transitions and showed isotropic transitions. As expected, all the viologen salts had excellent stabilities in the temperature range of 278–295 °C as determined by thermogravimetric analysis.

Thermotropic liquid crystalline properties of (hydroxypropyl)cellulose derivatives with butyryl and heptafluorobutyryl substituents

(Hydroxypropyl)cellulose (HPC) derivatives with butyryl (Bu) and heptafluorobutyryl (7FBu) substituents were prepared in various proportions of the Bu/7FBu groups and at a fixed total DS (DSBu + DS7FBu) of 3.0. Thermotropic liquid crystallinity of the derivatives (Bu7FBu-HPC) was investigated to specify the effect of the fluoroacylation on the mesophase behavior. Thermal transition data were collected using differential scanning calorimetry and polarized light microscopy. The Bu7FBu-HPC samples formed a chiral nematic phase between their glass transition and isotropization temperatures, Tg and Ti-a, respectively; these transition temperatures rose moderately as the 7FBu proportion increased (Tg = − 44 to − 27 °C and Ti-a = 158–190 °C for DS7FBu = 0.04–1.60). The structural property of the mesophase was examined at 70 °C by circular dichroism and other optical measurements. The chiral nematic pitch (P) sensitively increased with increasing 7FBu proportion, while the supramolecular helical arrangement remained right-handed. Selective light-reflection colors were observed for the samples of DS7FBu = 0.04–0.8, covering an entire spectrum range from violet to red. Temperature dependence of P was also examined for selected samples below Ti-a, and it was found to increase with increasing temperature; however, there was no indication of inversion in the handedness of the helical structure. Wide-angle X-ray diffractometry revealed that the increases of P responding to the increases in DS7FBu and temperature were attributable to the decrease of the twist angle between adjacent thin nematic layers.

Synthesis, mesomorphic properties and nonlinear optical studies of alkyl and alkoxy phenylacetylene containing phenazine fused extended triphenylene discotic liquid crystalline dyes

Herein, we have reported the alkyl and alkoxy phenylacetylene containing phenazine fused triphenylene discotic liquid crystals (DLCs) which are obtained by the condensation reaction of triphenylene-1,2-diquinone with 1,2-diamino-4,5-dibromobenzene, followed by Sonogashira C–C coupling reaction with 4-alkyl-phenylacetylene or 4-alkoxy-phenylacetylene. Six novel derivatives were synthesized and evaluated for their thermal and optical properties. They show a broad range of hexagonal columnar phase and retain their mesophase up to room temperature upon cooling from the isotropic liquid. Thermotropic liquid crystalline properties of all the compounds were studied by polarised optical microscopy (POM), differential scanning calorimetry (DSC). The self-assembly of mesophase structure was investigated by X-ray diffraction (XRD) studies. Thermogravimetric analysis of all the mesogens shows good thermal stability over a broad temperature range. The photophysical properties of newly synthesized compounds were measured using UV–Vis absorption and photoluminescence emission spectroscopy in anhydrous chloroform solvent. The π-extended conjugation in these mesogens exhibit strong absorption bands falling around 270–487 nm and corresponding emission band at 657–663 nm respectively. The high delocalization of π– electrons in extended discotic mesogens show high nonlinear optical properties when measured under excitation by nanosecond laser pulses at 532 nm. These materials may find distinctive applications in the semiconducting devices.

Thermotropic phase behavior and surface-active properties of alkoxyethyl α-d-glucopyranoside

To overcome the inherent weakness of the traditional alkyl α-d-glucopyranoside in water solubility and surface activity, a series of sugar-based surfactants alkoxyethyl α-d-glucopyranosides were successfully synthesized by introducing an oxyethene spacer (OCH2CH2). Herein, their thermotropic liquid crystalline and surface-active properties were investigated using DSC, POM and other methods. The phase transition temperature increased with increasing the alkyl chain length, meanwhile all glycosides were found to form the smectic phase since there was the typical focal-comic fan texture during cooling. Moreover, alkoxyethyl α-d-glucopyranosides had better water solubility and finer surface activity than that of the traditional alkyl α-d-glucopyranosides without an oxyethene fragment. Furthermore, the HLB number, solubility, CCMC value, γCMC value and Γmax value of alkoxyethyl α-d-glucopyranoside had a tendency to decrease with increasing the alkyl chain length, whereas the logP value, πCMC value, Αmin value and pC20 value showed the opposite trend with increasing the alkyl chain length. In addition, decyloxyethyl α-d-glucopyranoside showed the strongest emulsifying activity in n-octane/water system and rapeseed oil/water system, and it also had the best foaming properties. Therefore, an effective introduction of an oxyethyl fragment as a hydrophilic spacer indeed made an excellent contribution to improve water solubility and surface activity.

Mesomorphism dependence on central bridge and tail ended polar group

A novel azoester homologous series of laterally and terminally substituted viz, RO–C6H4–CH=CH–COO–C6H3–(CH3) –N=N–C6H4–Cl is synthesized, characterized and studied with a view to understand and establish the relation between molecular structure and thermotropic liquid crystalline property of its homologs. Series consists of twelve homologs. LC properties commence from very first member of a series and continue up to last homolog as enantiotropic nematic with absence of smectic property even in the monotropic condition. Transition temperatures of homologs were determined by polarizing optical microscopy equipped with a heating stage. The transition curves Cr?N and N?I behaved in normal manner. Thermal stability for nematic is 196.7?C whose mesophaselength ranges from 35°C to 131°C.

Thermotropic liquid crystalline and surface-active properties of n-alkyl α-d-mannopyranosides

A series of nonionic surfactants n-alkyl α-d-mannopyranosides (CnMan) with different alkyl chain length (n=6, 7, 8, 9, 10, 12, 14) have been prepared and the influence of the hydrophobic chain length on their thermal stability, thermotropic phase behavior and surface activity was studied, respectively. They showed fine thermal stabilities and smectic mesophase with TGA, DSC and POM methods. Meanwhile, the lamellar phase of CnMan (n=9, 10, 12, 14) was further confirmed by 2D-WAXD, which indicated that the arrangement of liquid crystal units was tilted and interdigitated layer-by-layer away from the layer normal. With increasing alkyl chain length of CnMan (n=9, 10, 12, 14), the layer d-spacing values of smectic phase increased gradually. Moreover, their HLB number, water solubility and surface tension decreased with increasing the alkyl chain length. Furthermore, their foaming properties increased with increasing the alkyl chain length. C9Man had the strongest foaming characteristic and an excellent foaming stability whereas C8Man and C9Man had the lowest surface tension (γCMC) in the same series. In addition, their emulsifying properties depended on the alkyl chain length and the corresponding oil/water system, C8Man and C9Man had stronger emulsifying activity in n-octane/water system, C9Man and C10Man had stronger emulsifying activity in rapeseed oil/water system.

Thermotropic liquid-crystalline properties of extended viologen bis(triflimide) salts

ABSTRACTA series of extended, symmetric viologen triflimides were synthesised by the metathesis reaction of lithium triflimide with the respective viologen tosyalates in methanol. Their chemical structures were characterised by Fourier Transform Infrared, 1H and 13C Nuclear Magnetic Resonance spectroscopy and elemental analysis. Their thermotropic liquid-crystalline (LC) properties were examined by a number of experimental techniques including differential scanning calorimetry, thermogravimetric analysis, polarising optical microscopy and variable temperature X-ray diffraction. The viologen salts containing alkyl chain of two carbon and three carbon atoms were relatively low melting salts. Those of alkyl chains of four carbon and five carbon atoms formed ionic liquids at 88 and 42°C, respectively. Those of alkyl chain of 9, 10 and 11 carbon atoms were high melting salts, as high as 166°C. Those of higher alkyl chains of 16, 18 and 20 carbon atoms showed thermotropic LC phases forming SmC, SmA and an unidentified smectic (SmX) phases, and showed SmA to isotropic transitions at high temperatures. As expected, all the viologen triflimides had excellent stabilities in the temperature range of 338–365°C.