Mesogenic Properties Research Articles

Mesogenic cholesterol-naphthalene dimers: Synthesis, characterization, mesogenic properties, photochromic behaviour and theoretical insights

Synthesis and characterization of two new series of unsymmetrical dimers combining cholesterol with azo (Series I-n) or azomethine (Series II-n) naphthalene moieties were reported. The chemical structures were confirmed using FT-IR, 1H NMR, 13C NMR, mass spectrometry, and elemental analysis. Their thermotropic properties were investigated using POM, DSC and XRD. The analysis revealed that the first lower members (n = 1,2) of each series lack mesogenic properties due to short, flexible spacers, while higher members (n = 3–5,7,9,10) exhibit enantiotropic chiral nematic phases. Notably, higher members with odd spacers (n = 5,7,9) also display SmC* phases, highlighting the influence of spacer length and odd–even effects on molecular interactions. Dimers from series I-n demonstrated slightly higher clearing temperatures (TN-Iso) compared to series II-n. UV–Vis spectroscopy showed trans–cis isomerization, with a photoconversion efficiency of 56.7 % for the I-7 dimer. Computational studies using the B3LYP functional with a 6-31g (d, p) basis set provided insights into the electronic structure through electrostatic potential (ESP) and optical property analysis.

Synthesis of new liquid crystal Schiff's bases bearing ester moiety, DFT calculation and mesomorphic studies

A new homologues series of liquid crystalline material (E)-4-(((3,4-dimethylphenyl) imino) methyl) phenyl4-n-alkoxybenzoate (SBn) synthesized. SBn compounds was subjected to analysis using infrared spectroscopy, proton magnetic resonance, 13C NMR, UV- visible and mass spectroscopy for characterization. The investigation of liquid crystalline phases and their transition enthalpies was carried out using a polarized optical microscope and differential scanning calorimetry, respectively. All compounds within the homologous series display mesogenic properties. The SB1 -SB7 homologues exhibit an enantiotropic nematic mesophase within the temperature range of 180–106 °C, while the SB14 -SB18 homologues show a smectic A mesophase at temperatures between 78 and 75 °C. Additionally, the SB8 -SB10 homologues exhibit a monotropic smectic A mesophase at 61–59 °C. The phase transitions observed in series SBn are compared with those of structurally related compounds to assess the influence of central linkage and lateral tail `substitution on their mesophase behavior. With the help of DFT; EHOMO and ELUMO energy gap were computed to be negative for all derivative molecules, indicating their stability and in the following order: SB4 > SB6 > SB8 > SB12. Dielectric through determined values of complex permittivity of the synthesised liquid crystal over a broad frequency range are reported. Determined static permittivity value of liquid crystal is 2.25, at room temperature. The compound SBn exhibited a relaxation peak in the dielectric loss spectra in the microwave frequency range, which may be assigned to the rotation of the end polar group of the molecule.

New Calamitic Mesogens Exhibiting Aggregation-Induced Emission (AIE).

Aggregation-induced emitters or AIEgens are generally signified by their stronger photoluminescence in aggregation than in the solution state. Due to high emission efficiency in aggregate and solid states and good processability, organic AIEgens drew attention to the development of advanced luminescent materials. However, as mesogenic materials self-assemble to a different molecular arrangement in different phases, achieving liquid crystallinity and AIE properties in the same molecule would provide a valuable tool to develop solvent-independent AIEgenic materials. With this goal, the present work reports the synthesis of new organic thermotropic liquid crystalline compounds exhibiting aggregation-induced emission (AIE). The synthesized compounds exhibit strong green luminescence in a solid state which sharply quenches upon entering smectic mesophase by heating. This is in addition to the exhibition of dispersion medium (solvent)-dependent emission, thus providing a dual mode of AIE. The mesogenic property of the synthesized compounds was studied by XRD, POM, and DSC. The AIE was studied by fluorescence spectroscopy and variable temperature fluorescence microscopy. A DFT study was carried out to gain an insight into the AIEgenic behavior of the material.

Smart design of highly luminescent octupolar mesogenic tetra styryl-alkynyl bipyrimidine-based chromophores presenting non-linear optical properties

The research investigations reported in this paper focuses on the influence of rational design on the photophysical properties of new all-organic multifunctional chromophores. Nonlinear optical (NLO) behavior, optical properties and mesogenicity of several new π-conjugated octupolar chromophores, presenting alkoxy styryl-alkynyl donor groups carrying aliphatic achiral and chiral chains in the 3,4/3,5/2,4 position, connected to electron-accepting 2,2-bipyrimidine cores are investigated by various techniques (light-transmission measurements, polarized-light optical microscopy, differential scanning calorimetry measurements, two-photon excited fluorescence and Hyper Rayleigh Scattering). The mesogenic properties were investigated depending on the position of the alkoxy chain and the 3,4 derivatives were found to exhibit liquid-crystal properties with the formation columnar phases over large temperature ranges which were confirmed by small-angle X-ray scattering analysis. All the molecules exhibit exceptional high fluorescence quantum yields values around 80 % and excellent nonlinear optical properties.

Mesomorphic and optical properties of azo-ester liquid crystalline reactive mesogens with enhanced thermal stability

A series of azo-ester-linked polymerizable liquid crystalline compounds M1-M3, containing lateral methyl substitution and different terminal alkoxy substituents, e.g., −OCH3, −OCH2CH3, and −OCH2CH2CH3 have successfully been synthesized and characterized. The chemical structures of the prepared compounds were confirmed by different spectroscopic techniques. Thermogravimetric analysis revealed that all the compounds exhibited excellent thermal stability and showed two-staged decomposition patterns. The optical microscopic study revealed that all compounds displayed only the nematic phase and lateral substituent played a crucial role in the formation of single mesophase. The broad X-ray scattering peaks for M1, M2, and M3 in the 2.5–5.5 nm−1 region was observed at temperatures of 154 °C, 85 °C, and 129 °C, respectively, upon cooling from the isotropic liquid, confirming the existence of nematic mesophase. The electronic spectra of M1-M3 showed two main absorption bands with λmax ranges of 263–266 and 369–377 nm. The E-Z photoisomerization study of M1-M3 showcased that the processes followed the first-order kinetic, and the isomerization rate decreased as the alkoxy chain length increased. On the contrary, the Z-E thermal isomerization rates for M1-M3 showed insignificant changes as the alkoxy chain length increased.

Symmetrical liquid crystalline dimers containing azo and azomethine linkages: synthesis, characterisation, mesomorphic study and DFT studies

ABSTRACT In the current study, one new series of symmetrical liquid crystalline homologous series of dimers with a rigid aromatic core with azo and azomethine group were synthesized using an ether-linking group. Several spectroscopic methods, including FT-IR, 1H-NMR, 13C-NMR and elemental analysis, were used to describe the synthesised dimers. The differential scanning calorimetry (DSC) and polarised optical microscopy (POM) were used to assess their mesomorphic properties. The results showed that the number of methylene spacers significantly affected the thermal properties of the synthesized dimers. To ascertain photophysical behaviour, UV-visible spectroscopy was employed. All the dimers of the present series show excellent enantiotropic nematic mesophase. The relationships between structure and its mesogenic property, the effects of various flexible spacers, the mesophase ranges, and the photo-isomerization of liquid crystalline dimers were all investigated. DFT study was carried out to gain a better understanding of structural features.

Synthesis, structure and mesogenic properties of benzoxazole derivatives

ABSTRACT Two new homologous series of mesogenic compounds, alkanoic acid 4-{[4-(6-chloro-benzooxazol-2-yl)-phenylimino]-methyl}-3-hydroxy-phenyl ester (3a-c) and alkcanoic acid 4-(6-chloro-benzooxazol-2-yl)-3-hydroxy-phenyl ester (5a-b) incorporating benzoxazole heterocyclic have been prepared and FT-IR, NMR, and MS spectrometry have been used to study the molecular structures. The mesogenic behaviour was examined using POM, DSC, and PXRD (variable temperature) techniques. To evaluate its impact on thermal behaviour and mesomorphic properties, the imine linking group of derivatives was modified and investigated. Enantiotropic SmA is observed by the members of Series-I, while those of series-II show monotropic SmA mesomorphism. These compounds were also examined for their absorption and fluorescent properties. The absorption and photoluminescence spectra of compounds 3a-c occurred at 345 nm and 410 nm, whereas in the case of 5a-b occurred at 325 nm and 370 nm respectively. The GAUSSIAN-09 programme has been utilised to perform DFT calculations at B3LYP level for the purpose of obtaining the stable electronic structures of 3a and 5a.

Synthesis, mesomorphic behaviour, and DFT studies of biphenyl bis-ester Schiff base liquid crystals

A novel series of calamitic liquid crystals with rod-like structures, derived from biphenyl bis-ester, has been successfully synthesized. This was achieved through the condensation reaction of [1,1′-biphenyl]-4-yl 4-formylbenzoate with n-alkyl 4-aminobenzoate, where n ranges from 2 to 8, 10, 12, 14, 16, and 18. The synthesized compounds were characterized using FT-IR, 1H NMR, 13C NMR, and mass spectroscopy techniques. The liquid crystal behaviour of all synthesized compounds was investigated using Polarizing Optical Microscopy (POM) and Differential Scanning Calorimetry (DSC). It was found that all compounds within the homologous series exhibited mesogenic properties. The effect of molecular flexibility on the mesophase type and transition temperature range was systematically explored. Some compounds displayed a nematic phase, while others showed characteristics of the smectic A phase; additionally, certain compounds exhibited properties of both the nematic and smectic A phases. Furthermore, utilizing B3LYP/6–31++G (d,p) basis sets DFT level calculations and complete geometric optimization of the synthesized compounds was conducted. This optimization facilitated the examination of optimized geometrical structures, aspect ratios, dipole moments, polarizabilities, Frontier molecular orbitals, and molecular electrostatic potentials through DFT calculations.

Theoretical prediction (DFT) and experimental observation of electronic and electro-optical properties of HATn (n = 5,6,7,8) molecules for optoelectronic applications

The formation of triphenylene core-based discotic mesogens exhibiting a classical columnar phase led to several superior electronic and optoelectronic applications. The present work reports the theoretical investigation of discotic hexaalkoxytriphenylene (HATn; n = 5, 6, 7, 8) mesogens including electro-optical, electronic, and thermodynamic properties using density functional theory (DFT) as a computational quantum mechanical tool. The various physical and chemical properties of these mesogens, such as electronegativity, specific heat capacity, polarizability, absorption, and dipole moment are calculated computationally and discussed in the study. The simulation study reveals the variation in physical properties either follows the odd–even effect or changes monotonically for HATn series. Experiment has been performed for comparison with the theoretical results. The physical and chemical properties of these discotic mesogens change with alkyl chain length variation and explain the structure–property correlation in the molecules. The obtained results of the designed molecular structure held promising applications for optoelectronic devices based on discotic mesogens.

Mesophase analysis, DFT calculation and microbial activity of a novel mesomorphic homologous series with ethyl 4-aminobenzoate

A novel homologous series of cinnamoyl ester comprising of elven (C1 to C16) homologues liquid crystal (LC) samples have been synthesized and characterized using instrumental methods (spectral and thermal) of analysis and DFT approach. As results, middle ordered melting type of series with exhibition of nematic mesophase were observed. The observed mesogenic properties and transition temperature are affected by the size of alkyl chains that shows mesomorphism is susceptible to molecular structure. The prepared LCs of cinnamoyl ester derivatives were further examined for their biological activities and the obtained results indicates a good biological potential for the studied LC materials.

Synthesis, chiral separation and physical properties of the cinnamic acid derivatives exhibiting short-pitch cholesteric and TGB phases

ABSTRACT Two new photosensitive chiral liquid crystalline materials derived from cinnamic acid were synthesised in (R) and (S) enantiomer forms. The materials were characterised by NMR spectroscopy, purified by preparative liquid chromatography, and the chemical purity of the final products was determined by high performance liquid chromatography (HPLC). High optical purity was reached for all enantiomers. The enantiomer elution order was confirmed by the analysis of non-racemic (R) and (S) mixed samples. The cinnamic acid derivatives are capable of undergoing photoisomerisation. Sample irradiation was performed to realise E-Z isomerisation and investigate its effect on the enantioseparation. The conditions of the enantioselective HPLC method were optimised to achieve a baseline separation for all studied materials both before and after irradiation by the UV light. The mesogenic properties of the studied enantiomers and their racemic mixtures were obtained from differential scanning calorimetry measurements, optical textures observed under the polarising light microscope and X-ray diffraction measurements. Cholesteric and TGB phases have been found for the enantiomers and, analogously, nematic and smectic phases have been confirmed for their racemates. The temperature dependence of the optical birefringence has been studied for the racemates in the temperature range of the 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.

Odd-even effect in chiral side-chain cyanobiphenyl block copolymer assemblies prepared by polymerization-induced chiral self-assembly.

The precise control of the chirality of polymer assemblies is a challenge faced by scientists and has received significant attention in recent years. In this study, we employed the polymerization-induced chiral self-assembly (PICSA) method to create chiral side-chain cyanobiphenyl (CB) block copolymer (BCP) assemblies. The flexible spacers in chiral CB monomers were regulated to exhibit two distinct odd-even effects in the supramolecular asymmetrical arrangement of the CB mesogens inside BCP assemblies. The research results indicated that the liquid crystalline properties of CB mesogens significantly influence the magnitude and sign of their chiroptical properties. These findings have significant implications for the design of polymer assemblies with designable chiroptical functions.

Synthesis, characterization, mesogenic properties, and DFT studies of unsymmetrical liquid crystalline dimers of biphenyl

ABSTRACT A series of asymmetrical liquid crystal dimers (E)-4((4(n([1,1’-biphenyl]-4-yloxy)alkoxy)phenyl) diazenyl)benzonitrile (BpnCN) were synthesized, consisting of two distinct rigid cores: 4-cyanoazobenzene and biphenyl units. Characterization was accomplished through various spectroscopic techniques. The mesomorphic properties were explored via polarizing optical microscopy and differential scanning calorimetry. UV–Visible spectroscopy assessed the photophysical properties. The presence of an even number of atoms in the flexible spacer resulted in linear molecular shapes for Bp4CN and Bp6CN, while Bp3CN and Bp5CN showed nonlinearity, explaining their non-mesomorphic properties. Computational studies showed a clear correlation between theoretical and experimental wave numbers. The enhanced stability of the mesophase in Bp4CN and Bp6CN was attributed to their higher aspect ratios, promoting ordered structures within the material. UV–visible spectroscopy of dimer Bp4CN revealed absorption bands at 445 nm (n–π* transitions) and 365 nm (π–π* transitions), with photoisomerization observed under UV exposure, reaching a photostationary state in 2.5 min and reversible isomerization back to the trans form in approximately 2.3 h. Notably, even in the absence of substitutions on the biphenyl core, the dimers in our present series demonstrated an enantiotropic nematic mesophase.

The effect of fluorination on the liquid crystal and optical behaviors of amphiphilic cyanostilbene-based mesogens

Three series of amphiphilic mesogens containing a cyanostilbene core with zero, one or two lateral fluorine atoms, which attach one polar glycerol group at one end and three lipophilic alkyl chains at the other end were synthesized by Suzuki coupling and Knoevenagel reactions. The thermodynamics, liquid crystalline and photophysical properties of these amphiphilic mesogens were evaluated by polarized optical microscopy, differential scanning calorimetry, small-angle X-ray diffraction, density functional theory calculation, absorption and emission spectra. The non-fluoro and mono-fluoro amphiphilic mesogens display a mesophase transition from hexagonal columnar phase to three-dimensional micellar cubic phase with Im3¯m lattice by the increase of temperature or the elongation of terminal lipophilic alkyl chains. The bi-fluoro amphiphilic mesogens can only self-organize into hexagonal columnar mesophase. Similar spectral properties and weak solvatochromism in these amphiphilic mesogens are observed attributed to the weak intramolecular charge transfer and weak influence of fluorine atom on the electronic properties in both ground and excited states. In addition, aggregation-induced emission behavior could be achieved in these amphiphilic mesogens due to the twisted molecular configuration. Therefore, complex self-assembly structures and interesting photophysical properties may be altered by varying the degree of fluorination of amphiphilic mesogens, which could promote the application of liquid crystalline materials.

Evaluation of Luminescent and Mesogenic Properties of Europium(III) Binuclear Complexes According to Quantum Chemical Calculations

Evaluation of Luminescent and Mesogenic Properties of Europium(III) Binuclear Complexes According to Quantum Chemical Calculations

Unsymmetrical liquid crystalline dimers containing biphenyl moiety: synthesis, characterisation, mesomorphic study and DFT studies

ABSTRACT In the current study, two new unsymmetrical liquid crystalline homologous series of dimers with a rigid biphenyl core were synthesised using an ether-linking group. Several spectroscopic methods, including FT-IR, 1H-NMR, 13C-NMR, elemental analysis and mass spectrometry, were used to describe the synthesized dimers. Differential scanning calorimetry (DSC) and polarised optical microscopy (POM) were used to assess their mesomorphic properties. The results showed that the number of methylene spacers significantly affected the thermal properties of the synthesized dimers. To ascertain photophysical behaviour, UV–Visible spectroscopy was employed. Nematic-type mesophase patterns with good mesophase range and thermal stability were seen in both series. Dimers with flexible spacers ( n = 2, 4, 6) had the best liquid crystalline nature out of all the dimers. The relationships between structure and its mesogenic property, the effects of various flexible spacers, the mesophase ranges, and the photo-isomerization of liquid crystalline dimers were all investigated. DFT Studies were carried out to gain a better understanding of structural features.

Synthesis and self-assembly properties of the first fluorescein-based hexacatenar mesogens

First series of fluorescein-based hexacatenar mesogens consisting of a central fluorescein unit and two 1,2,3-triazole dendritic wings were designed and synthesized by using the Williamson reaction and Cu-assisted alkyne-azide cycloaddition reaction. Polarized optical microscopy textures, differential scanning calorimetry curves, and X-ray diffraction (XRD) data demonstrated that all the compounds can self-assemble into hexagonal columnar mesophases. Organogel test demonstrated that these compounds could form organogel in some moderate polar solvents with irregularly winkled morphologies. Density functional theory calculation demonstrated that these mesogens adopted distorted conformation which might be the reason why narrow mesogenic temperature ranges and irregularly winkled morphologies in these compounds are observed.

Revisiting a family of liquid crystalline methacrylic phenyl benzoate monomers

The synthesis and phase characterization of a homologous series of 4′-alkyloxyphenyl 4-(6-(methacryloyloxy)hexyloxy))benzoate monomers have been carried out. The characterization comprises polarizing optical microscopy (POM), differential scanning calorimetry (DSC) and temperature dependant small and wide-angle x-ray scattering (SAXS –WAXS). The X-ray data and POM images reveal both the nematic and monolayered orthogonal smectic A phase in M6En series. The monomers with a terminal chain length from five to twelve carbon atoms exhibit a wide temperature range of a stable smectic A phase with a narrow intervening nematic phase at higher temperatures. On cooling down from the isotropic phase the temperature range of the nematic and smectic A phase considerably increases. The specific features of the phase diagram and mesogenic properties of M6En series are discussed in terms of the peculiar molecular structure of these monomers.

Liquid crystalline naphthyl derivatives with bromoalkoxy tail: Photophysical behavior and DFT studies

One new homologous series of mesogenic bromoalkoxy terminated naphthyl derivatives containing flexible spacers as well as azo and ether linkages was synthesized by the etherification of an azo dye (E)-4-(naphthalen-2-yldiazenyl) phenol with various α, ω-dibromo-alkanes, respectively. Compounds in the present work were convinced with respective right structures confirmed with various spectroscopic techniques. Thermotropic properties of the compounds were investigated. Among all the compounds, compounds with flexible spacer (n = 4, 5, 6) exhibited excellent liquid crystalline nature. Structure–property relationships, the influence of different flexible spacers, the mesophase ranges and the photo-isomerization of liquid crystalline compounds were studied. The photophysical behavior was gained by UV–visible spectroscopy and optical properties were determined with a spectroscopic ellipsometer. Computational studies of all molecular structures were performed with satisfactory explanation to attribute mesogenic and optical properties. It's worth noting that synthesized mesogenic materials are excellent dielectrics making them suitable for electronic and industrial applications, as well as having a suitable refractive index making them suitable for light-guiding phenomena.