Mesophase Temperature Research Articles

Synthesis and Properties of Highly Tilted Antiferroelectric Liquid Crystalline (R) Enantiomers.

This work reports the synthesis method and various properties of four rod-like antiferroelectric (R) laterally substituted enantiomers, with or without fluorine atoms used as substituents in the benzene ring. The influence of fluorine substitution on the mesophase temperature range was determined. The synthesized compounds are three-ring rod-like smectics with a chiral center based on (R)-(-)-2-octanol. Their chemical and optical purity was checked using high-performance liquid chromatography (HPLC). Two newly synthesized enantiomers and three previously reported (R) enantiomers were used to formulate two antiferroelectric mixtures. The mesomorphic behavior was characterized by polarizing optical microscopy, differential scanning calorimetry, and X-ray diffraction (XRD). The helical pitch and tilt angle measurements were done using the selective light reflection phenomenon and the electro-optical method, respectively. All the enantiomers exhibit a wide temperature range of the antiferroelectric phase, with a high tilt angle. Furthermore, the enantiomer with lateral fluorine substitution in the ortho position has a very long helical pitch (more than 2.0 µm), relatively low enthalpy of melting point, and a tilt angle close to 45 degrees. The designed (R) enantiomers can be useful for formulating eutectic mixtures for further use in various devices, including photonics and optoelectronics.

Differences Photopolymerizations and Characterizations of Monomers Liquid Crystal between Mesogen Reactive RM 257 and Cholesteryl Acrylate using method of UV Curing

Abstract Mesogen reactive RM257 and cholesteryl acrylate are two types of liquid crystal with the characteristic property of possesing polymerizable groups. Cholesteryl acrylate has interesting properties that can form a helical spiral structure. Previous research in maintaining the helical structure has not been maximized. In this study, we will explain how the UV curing process is a way to fix the helical structure. Monomer phase of cholesteryl acrylate only appears at mesophase temperature, in order to maintain the helical structure of the cholesterl acrylic compound is polymerized. Mesogen reactive RM257 is monomer liquid crystal that acrylate functions as back bone polymer chain. Cholesteryl acrylate and RM257 each monomers is polymerized using UV light with 55 watt of wavelength which has 365 nm. The polymerization process produces a new functional group formed by C-O esters at wave numbers 1047 cm−1 and 1055 cm−1. XRD diffraction pattern showed peaks at 2θ in 7.5°,15°, and 20°. Photo SEM image showed crosslinked morphology structure. Based on the results of this study, it is hoped that the polymer RM257 and acrylate coliform can be smart materials for sensor applications and further technological material composites.

New Molecularly Flexible Self-Assembling Benzothiadiazole Derivatives: Mesomorphism And DFT Investigations

In the present study, we have synthesized symmetric/unsymmetrical BTD embedded self-assembling molecules and investigated for their mesomorphic properties. Two symmetrical series (BTDK-(2-18) and BTDC-(4-18)) comprises benzothiadiazole moiety as a central core unit which is connected to two different systematically varied end-groups, alkoxy ester and alkoxy coumaryl unit connected through ether and imine linkages. On the other hand, the asymmetric molecules have an alkoxy chalconyl unit at one end and a formyl group at the other. It was observed that, the mesomorphism is completely depends on the molecular flexibility. New molecules revealed mesomorphic behaviour with N (nematic), SmA (smectic-A) and SmC (smectic-C) mesophase with high thermal stability and greater range. Changes in mesogenic units (alkoxy ester & alkoxy coumaryl unit) and the impact of altering the alkoxy chain at both ends have been investigated. Interesting evaluation has been carried out on the molecular flexibility which resulted in different mesomorphic behaviour of molecules under study. Furthermore, the experimentally established values of the mesophase thermal stability (Tc) and mesophase temperature ranges (ΔTSmA, ΔTSmC, and ΔTN), as well as the type of the mesophase, were related to the calculated quantum chemical parameters (Frontier molecular orbitals (FMOs), Aspect Ratio, Polarizability, dipole moment, molecular and electrostatic potential (MEP)) that were obtained by using the DFT method of the investigated compounds.

New Series of Hydrogen-Bonded Liquid Crystal with High Birefringence and Conductivity.

Liquid crystals with high dielectric anisotropy, low operational thresholds, and significant birefringence (Δn) represent a key focus in soft matter research. This work introduces a novel series of hydrogen-bonded liquid crystals (HBLCs) derived from 4-n-alkoxybenzoic, 4-alkoxy-3-fluorobenzoic derivatives (nOBAF), 4-alkoxy-2,3-fluorobenzoic derivatives (nOBAFF), and 2-fluoro-4-nitrobenzoic acid. The HBLCs were characterized using Fourier transform infrared spectroscopy, and their thermal behavior was evaluated via differential scanning calorimetry. Optical observations were conducted using polarized optical microscopy. The results indicate that mixtures containing benzoic acid with a bilateral fluorine substituent exhibit both SmA and SmC phases, while those with a unilateral fluorine substituent exhibit nematic and SmA phases. Moreover, an increase in the length of the alkoxy chain results in an expanded mesophase temperature range. This study demonstrates that the presence of a fluorine substituent and the incorporation of an NO2 group in the molecular structure result in an increase in dielectric permittivity, DC conductivity, dielectric anisotropy, and birefringence.

Columnar Mesomorphism in a Methylthio-Decorated Triindole for Enhanced Charge Transport.

We report a semiconducting triindole-based discotic liquid crystal (TRISMe) functionalized with six p-methylthiophenyl groups at its periphery. While initially a crystalline solid at room temperature, TRISMe transitions to a columnar hexagonal mesophase upon heating and retains this supramolecular organization upon subsequent cooling, despite having only three flexible alkyl chains attached to the core's nitrogens. The incorporation of methylthio groups effectively hinders tight molecular packing, stabilizing the columnar arrangement of this disk-shaped molecule. Single crystal analysis confirmed the high tendency of this compound to organize into a columnar architecture and the role played by the methylthio groups in reinforcing such structure. The mesomorphic behavior of TRISMe provides an opportunity for processing from its molten state. Notably, our research reveals significant differences in charge transport depending on the processing method, whether solution drop-casting or melt-based. TRISMe shows hole mobility values averaging 3 × 10-1 cm2 V-1 s-1 when incorporated in diode-type devices from the isotropic melt and annealed at the mesophase temperature, estimated by SCLC (space-charge-limited current) measurements. However, when integrated into solution-processed organic field-effect transistors (OFETs), crystalline TRISMe exhibits a hole mobility of 3 × 10-4 cm2 V-1 s-1. The observed differences can be attributed to a beneficial supramolecular assembly achieved in the mesophase in spite of its lower order. These results emphasize the material's potential for applications in easy-to-process electronic devices and highlight the potential of methylthio moieties in promoting columnar mesophases.

Azo-linked room temperature columnar liquid crystals with bisphenol A core: Structure property relationship and photophysical properties

A series of bent-shaped liquid crystals containing an azo group and a bisphenol A core were synthesized, and characterized using various techniques. The presence of mesogenic properties in these azo-based dimers was confirmed through POM, DSC, and high-temperature XRD analysis. The structure-property relationship is further studied to confirmed the effect of the variable alkyl side chain on the terminal position, which also affects the liquid crystalline properties of the compounds in terms of mesophase temperature range and thermal stability. All the compounds exhibited enantiotropy columnar hexagonal phase with wide temperature range and thermal stability. Their photophysical properties were investigated using UV–visible spectroscopy and spectrofluorometry. It was observed that all four columnar mesogens underwent cis and trans azo isomerization upon exposure to photoisomerization.

Synthesis and characterization of acrylamide substituted sulfanilamide based calamitic LCs: effect of terminal group on phase behavior

In the present study, we have prepared two phenyl ring substituted sulfanilamide bearing acrylamide linking groups. The four derivatives (C1-C4) were prepared by changing the left n-alkoxy terminal group. The liquid crystalline properties of the synthesized sulfanilamide-based compounds were investigated using POM and DSC studies. All four materials exhibit nematic liquid crystalline properties during both heating and cooling. They also demonstrate a broad temperature range and thermal stability. Further, we have studied the structure-property relationship to gain a better understanding of the effect of the linking group and variable alkoxy tail group on mesomorphic behavior. The results indicate that thermal stability, mesophase temperature range, and liquid crystalline properties depend on the linking group and variable alkyl chain length.

Physical and Thermal Characterizations of Newly Synthesized Liquid Crystals Based on Benzotrifluoride Moiety.

The mesomorphic stability and optical activity of new group-based benzotrifluoride liquid crystals, (E)-4-(((4-(trifluoromethyl) phenyl) imino) methyl) phenyl 4-(alkyloxy)benzoate, or In, were investigated. The end of the molecules connected to the benzotrifluoride moiety and the end of the phenylazo benzoate moiety have terminal alkoxy groups which can range in chain length from 6 to 12 carbons. The synthesized compounds' molecular structures were verified using FT-IR, 1H NMR, mass spectroscopy, and elemental analysis. Mesomorphic characteristics were verified using differential scanning calorimetry (DSC) and a polarized optical microscope (POM). All of the homologous series that have been developed display great thermal stability across a broad temperature range. Density functional theory (DFT) determined the examined compounds' geometrical and thermal properties. The findings showed that every compound is entirely planar. Additionally, by using the DFT approach, it was possible to link the experimentally found values of the investigated compounds' investigated compounds' mesophase thermal stability, mesophase temperature ranges, and mesophase type to the predicted quantum chemical parameters.

A new conformationally symmetrical calix[4]pyrrole based supramolecular systems for liquid crystalline and window layer solar cell applications.

A newly symmetrical liquid crystalline compounds (CPB1-CPB4) based on calix[4]pyrrole as a central rigid core were synthesized via esterification reaction. All four compounds exhibit columnar hexagonal phase over a higher mesophase temperature range and stabilized mesophase upto room temperature. The thermal behaviors and optical textures were identified by using differential scanning calorimetry, Polarizing optical microscopyand the molecular organization of the compound in the mesogenic state is confirmed by X-ray diffraction technique. The molecular system based on calix[4]pyrrole core with symmetrical nature exhibited columnar type self-assembly at room temperature. All four supramolecules with different side spacer showed higher thermal stability. Based upon the optimization, compound CPB2 istested in accordance with the optical window layer in thin films solar cell devices. The calix[4]pyrrole functionalized supramolecular liquid crystalline compound based thin films showed suitable transmittance, optical energy band gap together with absorbance and extinction. The linear dependence of current on the voltage demonstrated Ohmic behavior of the CPB2 films. The surface morphology to the developed samples designated nearly uniform deposition of the CPB2 thin films together with grain growth. The findings warrant suitability of the films to implicate these as an eco-friendly optical window layer in thin films based solar cells.

Shaping 1,2,4-Triazolium Fluorinated Ionic Liquid Crystals

The synthesis and thermotropic behaviour of some di-alkyloxy-phenyl-1,2,4-triazolium trifluoromethane-sulfonate salts bearing a seven-carbon atom perfluoroalkyl chain on the cation is herein described. The fluorinated salts presenting a 1,2,4-triazole as a core and differing in the length of two alkyloxy chains on the phenyl ring demonstrated a typical liquid crystalline behaviour. The mesomorphic properties of this set of salts were studied by differential scanning calorimetry and polarized optical microscopy. The thermotropic properties are discussed on the grounds of the tuneable structures of the salts. The results showed the existence of a monotropic, columnar, liquid crystalline phase for the salts tested. An increase in the temperature mesophase range and the presence of two enantiotropic mesophases for the sixteen-atom alkyloxy chain salt can be observed by increasing the length of the alkyloxy chain on the phenyl ring.

Synthesis and physico-chemical properties of dilateral flouro azo/ester four aromatic ring mesogens and their mixtures of liquid crystals

ABSTRACT Four series of di-flouro, namely; 4-substituted phenylazo-3-flouro phenyl-4′-n-alkoxy 3-flouro phenylazo benzoates (I n a-d) based on aromatic rings with the azo/ester/azo linkages core, were prepared and investigated for their mesomorphic properties. An alkoxy group with chain length varied from n = 6 to 16 is attached to the terminal phenylazobenzoate moiety and the other terminal is a compact group (X = –CH3O, –CH3, H and Br) attached to phenylazo moiety. The mesophases were investigated by DSC and POM and compared with previously investigated dilaterally methyl substituted analogues. Terminally unsubstituted and Br substituted analogues displayed dimorphic N and SmA phases, except the lower homologue (n = 6), while terminally – CH3O analogues exhibited monomorphic N phase. For terminally – CH3 substituted, compounds with n = 6–12 exhibited only N phase, while compounds with n = 14 and 16 displayed N and SmA phases. Meanwhile, the dilateral F substituents result in an enhancement in clearing thermal transitions compared with dilateral methyl substituents with a wide mesophase range. TGA analysis revealed that the prepared compounds are thermally stable within mesophase temperature range, except – CH3O, –CH3 and Br derivatives with n = 6. Binary mixtures of I6 a-d/I16 a-d derivatives were investigated. The photo-physical property was also studied.

Synthesis, Mesomorphism, Photophysics, and Device Properties of Liquid-Crystalline Pincer Complexes of Gold(III) Containing Semiperfluorinated Chains.

Gold(III) complexes of C∧N∧C-coordinating 2,6-diphenylpyridine pincer ligands with arylacetylide co-ligands are known triplet emitters at room temperature. We have reported previously that by functionalizing both the pincer ligand and the phenylacetylene with alkoxy chains, liquid crystallinity may be induced, with the complexes showing columnar mesophases. We now report new derivatives in which the phenylacetylene incorporates one, two, or three 1H,1H,2H,2H-perfluoroalkyl chains. In terms of intermolecular interactions, solution 1H NMR experiments suggest that the semiperfluoroalkyl chains promote a parallel, head-to-head arrangement of neighboring molecules relative to one another, rather than the anti-parallel, head-to-tail orientation found for the all-hydrocarbon materials. In terms of the liquid crystal properties, the complexes show columnar phases, with the addition of the more rigid fluorocarbon chains leading to a stabilization of both the crystal and liquid crystal mesophases. Mesophase temperature ranges were also wider. Interestingly, the amphiphilic nature of these complexes is evident through the observation of a frustrated columnar nematic phase between a Colr and a Colh phase, an observation recently reported in detail for one compound (Liq. Cryst., 2022, doi: 10.1080/02678292.2021.1991017). While calculation shows that, despite the “electronic insulation” provided by the dimethylene spacer group in the semiperfluoroalkyl chains, a small hypsochromic shift in one component of the absorption band is anticipated, experimentally this effect is not observed in the overall absorption envelope. Complexes with substituents in the 3,3′,4,4′-positions of the phenyl rings of the pincer ligand once more show higher-luminescence quantum yields than the analogues with substituents in the 4,4′-positions only, associated with the lower-energy-emissive state in the former. However, in contrast to the observations with all-hydrocarbon analogues, the luminescence quantum yield of the complexes with 3,3′,4,4′-substitution on the pincer increases as the number of semiperfluoroalkyl chains on the phenylacetylide increases, from 20% (one chain) to 34% (three chains). External quantum efficiencies in fabricated OLED devices are, however, low, attributed to the poor dispersion in the host materials on account of the fluorinated chains.

Synthesis and characterization of Liquid crystalline Cholesteric polysiloxane derivatives

ABSTRACT In this paper, two series of cholesteric liquid crystal polysiloxanes (PA and PB series) with selective reflection were synthesised. PA and PB series were both prepared by hydrosylation of monomer MA containing cholesterol, monomer MB containing D (+)-camphoric acid and 6-bromohexene (6-Br), besides PB series containing MC with cyano-group. The optical performance and thermal stability of PA and PB were observed, and the relationship between PB series and PA series was also studied. Tests such as POM, TGA, DSC and selective reflection showed that the polymers exhibited colourful Grandjean texture and excellent thermal stability. The Tg, Ti and the mesophase temperature for the PA series all tended to increase, and with the increase of steric hindrance of MB, the selective reflection may exhibit more difficulty. The PB series could dilute the steric hindrance of chiral monomers due to the introduction of cyano-group and the decrease content of MB, which not only guaranteed the polymer with wider mesophase temperature but also was conducive to appear the selective reflection and last longer, besides, with the temperature increased, the wavelength of the reflected light intended to blue shift compared to that of PA series with the same chiral contents.

Control of smectic layering in mono- vs disaccharide-coated polydiacetylenes

ABSTRACT Amphiphilic sugar-functionalised diacetylene lipids undergo facile self-organisation in the solid state, enabling a photo-initiated polymerisation, leading to the formation of sugar-coated polydiacetylenes. The presence of hydrophilic sugar moiety and the long aliphatic chains promote amphiphilicity-driven mesomorphism in these polymers. Maintaining the lyophilic segment uniform, glycolipids that vary in their sugar constitution are prepared, in order to assess mesomorphic changes with respect to varying sugar segment. Mono- and disaccharides are chosen that allow further to identify the changes in the emerging mesomorphic property with the sugar configurations. Whereas a smectic layering is observed common in these glycolipid polymers, the mesophase temperature range and the structural ordering are observed to vary depending on the sugar segment, as adjudged by optical polarising microscopy, calorimetry and X-ray diffraction assessments. Higher clearing temperatures are seen for disaccharide containing glycolipid polymer, as compared to the monosaccharide containing polymer. Further, in conjunction with energy minimised structures, interdigitised lamellar structure is inferred to the polymers.

Steric effect of di-lateral methyl substituent on the mesophase behavior of four-ring azo/ester/azo homologues

ABSTRACT Four series of azo/ester/azo four-rings homologues, namely, 4-substituted phenylazo-3-methyl phenyl-4′-n-alkoxy 3-methyl phenylazo benzoates (I n a-d), bearing two terminals substituents, the first is a compact polar group (X = methoxy, methyl, H and bromo) and the other terminal is an alkoxy group of varying chain length (n = 6 to 16), were prepared and their molecular structures confirmed. Their thermotropic behaviours were analysed with differential scanning calorimetry (DSC) and polarising optical microscopy (POM). TGA analysis revealed that the prepared materials are thermally stable within their mesophase temperature range. Irrespective of the polarity of X and/or the alkoxy chain length all compounds showed to display a nematic phase with high thermal stability and wide temperature range. The methoxy homologues showed to exhibit higher thermal stabilities. Comparing the nematic stability of the di-laterally dimethyl substituted (I n c) derivatives with X = CH3, with their previously reported mono-laterally methyl-substituted analogues (II n c) revealed that I nc homologues have thermal stabilities and mesophase temperature ranges lower than their corresponding analogues II n c. The effect of introducing the two lateral methyl groups on the extent of anisotropic polarisability of the whole molecule was discussed and their effect on the mesophase behaviour investigated. The photo-physical property was studied via UV-vis spectroscopy.

Correlation of self-assembly and thermal conducting properties of PEG-backbone polyether with a room temperature mesophase

A series of side chain liquid crystalline polymers with a cyanobiphenyl moiety was synthesized, and it showed considerably high thermal conductivity (∼0.46 W m−1 K−1) based on self-assembled microstructure developed by room temperature mesophase.

Aroyloxycinnamates with wide mesophase temperature ranges

ABSTRACT A new series of eight asymmetric homologues was designed and synthesised by the reaction of aroyloxybenzaldehydes with Wittig salt of methyl bromoacetate, where the length of the alkoxy chain was varied. All the compounds were found thermally stable up to 220°C. Differential scanning calorimetry, polarising optical microscopy and X-ray diffraction were used to study the mesomorphic properties, where a mesophase range of up to 80°C was obtained. The two shorter homologues with C3–C4 were nematic, the intermediate lengths were nematic and smectic A (SmA) with a progressive increase of the SmA domains and the longest homologue with C12 was purely SmA. The translational order parameter of the SmA mesophases showed that the molecular order inside the smectic layers increases with molecular length, associated with the higher stabilisation and predominance of the SmA phase. All compounds dispersed in solution absorb light in the ultraviolet region.

Novel fluorescent columnar liquid crystal based on tetraphenylethylene- rufigallol-tetraphenylethylene triads

In this article, two new tetraphenylethylene- rufigallol-tetraphenylethylene triads 7a and 7b were synthesized in yield of 50%. These compounds were characterized by mass spectrometry, NMR spectroscopy, and elemental analysis. Their mesomorphic behaviors were studied by polarizing optical microscopy, differential scanning calorimetry, and X-ray diffractometry. Investigation of their liquid crystalline behaviors indicated that compounds 7a and 7b possessed the hexagonal columnar mesophase. Compound 7b with dodecyl chains exhibited the low phase transition temperatures and wide range of mesophase temperatures in comparison with compound 7a. Compounds 7a and 7b exhibited excellent aggregation-induced emission in H2O/THF solution. The fluorescence quantum yields of these compounds in the solid state were 22% and 16%, respectively. Results from this study suggest that symmetrical trimer was a good approach to construct novel fluorescence columnar liquid crystals.

Thermal and Mesomorphic Investigations of 1:1 Supramolecular Assemblies of 4-[(4-(n-Alkoxy)phenylimino)methyl]benzoic Acids Having Symmetrical and Un-Symmetrical Terminal Chain Lengths

Thermal and mesomorphic properties of possible 1:1 supramolecular complexes (SMCs) (Im/In) designed from two members of 4-[(4-(n-alkoxy)phenylimino)methyl]benzoic acid with symmetrical or un-symmetrical alkoxy terminal flexible chains (carbons of m and n = 6, 8 and 16), were analyzed by differential scan-calorimetry (DSC), thermogravemetric (TG) analysis, and their mesophases identified by polarized optical microscopy (POM). The equimolecular mixtures of the two acids possess symmetrical and un-symmetrical terminal lengths. The mesomorphic properties of the binary mixtures were examined as a function of the total alkoxy chain length on both sides. Results revealed that the nematic mesophase temperature range increases as the total terminal length increases for all designed un-symmetrical mixtures. A comparison was constructed between the formed SMCs and of those of the previously prepared 4-n-alkoxyphenylazo benzoic acids as well as the 4-n-alkoxy benzoic acids, to examine the impact of mesogenic core on the mesomorphic properties. The comparison indicated that as the mesogenic portion lengthens the thermal mesophase stability exhibits higher values of phase transition temperatures; whereas, the azo and Schiff base moieties exhibited near thermal properties.

Columnar Liquid Crystalline Corannulenes: Synthesis, Assembly and Charge‐Carrier Transport Properties

Main observation and conclusionTwo discotic liquid crystalline (LC) molecules consisting of a bowl‐shaped corannulene core and five‐fold photoactive azobenzene branches with different paraffinic side chains were developed. Their self‐assembly, photo‐responsive behavior and charge‐carrier transport properties were investigated in detail. A wider mesophase temperature range was achieved when utilizing longer and furcal flexible side chain substitution. 2D XRD measurements revealed the π‐packed corannulene‐centered 1b (i.e., with furcal side alkoxyl chains) exhibited helical columnar LC phase. This packing structure also led to a higher hole charge carrier mobility of 7.07 x 10–2 cm2·V–1·s–1 compared to that of the counterpart 1a with linear side chain substitutions.