Search Results (37)

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. Full article

Azo-Schiff bases contain an azo photochrome showing isomerization accompanying with color change, and an imine moiety (which can contribute to the metal complexation capability). The syntheses of these molecules will be described, and their dyes applications will be discussed, such as for fuel cells, as photometric or colorimetric sensors. In addition, liquid crystals and their antibacterial efficiencies will also be discussed. Full article

A new class of Schiff base/ester compounds: ICln, 4-((2′-chlorophenylimino)methyl)phenyl-4″-alkoxy benzoates, were synthesized and their mesophase characteristics and thermal behavior were evaluated. Differential scanning calorimetry (DSC) was used to study mesophase transitions, and polarized optical microscopy was carried out to identify the phases (POM). The results show that all compounds are monomorphic, and enantiotropic nematic (N) phases were seen at all side chains. It was found that lateral Cl atoms in the terminal benzene ring influence both conformation and mesomorphic properties. Comparisons between the present investigated lateral Cl derivatives and their laterally neat, as well as their isomeric, compounds have been briefly discussed. Results revealed that the insertion of lateral Cl substituent in the molecular structure impacts the type and stability of the formed mesophases. The exchanges of the ester-connecting moiety improve their thermal nematic stability than their previously prepared structurally isomeric derivatives. These compounds exhibit a broad absorption in the UV-Visible region, including a peak in UV region and a tail around 550 nm, and there were observed to be absorption tail increases and energy band gap decreases with the increase of the alkoxy side chain length. The photoluminescence (PL) intensity was noted to be quenched for the bulky alkoxy group ascribed to non-radiative recombination through the defect states. Moreover, time resolved fluorescence decay spectra reveal that both the radiative and non-radiative recombination lifetime increases with the increase of alkoxy side chain length. Full article

The effect of the terminal benzyloxy group on the mesomorphic properties of liquid crystalline materials developed from rod-like Schiff base has been described. For this objective, a novel Schiff base liquid crystal family, specifically new series of Schiff base liquid crystals, namely, (E)-4-(alkyloxy)-N-(4-(benzyloxy)benzylidene)aniline, I_n, are prepared and investigated in detail. The length of the terminal alkyloxy chain (n) varies amongst the compounds in the series. Where n varies between 6, 8 and 16 carbons. At the other end of the compounds, benzyloxy moiety was attached. The molecular structures of all synthesized compounds were established using different spectroscopic techniques. The molecular self-assembly was explored using differential scanning calorimetry (DSC) and polarized optical microscope (POM). Depending on the length of the terminal alkyloxy chain, only one type of SmA phase with different stability was observed. The previously reported para-substituted systems and the present investigated compounds were compared and discussed. The calculated quantum chemical parameters were computationally correlated using the DFT method via the B3LYP 6-311G(d,p) basis set. The theoretical computations revealed that the length of the alkyl side chain influences the zero-point energy, reactivity and other estimated thermodynamic parameters of benzoyloxy/azomethine derivatives. Furthermore, the FMO energy analysis shows that molecule I₁₆ have higher HOMO energies than the other compounds, and I₆ has a much lower LUMO level than the rest. Full article

The experimental and theoretical study of influence of the conformational state and association on the chirality of the stereochemically nonrigid biologically active bis-camphorolidenpropylenediamine (CPDA) and its ability to induce the helical mesophase of alkoxycyanobiphenyls liquid–crystalline binary mixture was carried out. On the basis of quantum-chemical simulation of the CPDA structure, four relatively stable conformers were detected. A comparison of the calculated and experimental electronic circular dichroism (ECD) and ¹H, ¹³C, ¹⁵N NMR spectra, as well as specific optical rotation and dipole moments, allowed to establish the most probable trans-gauche conformational state (tg) of dicamphorodiimine and CPDA dimer with a predominantly mutually parallel arrangement of molecular dipoles. The induction of helical phases in LC mixtures based on cyanobiphenyls and bis-camphorolidenpropylenediamine was studied by polarization microscopy. The clearance temperatures and the helix pitch of the mesophases were measured. The helical twisting power (HTP) was calculated. The decrease in HTP with increasing dopant concentration was shown to be connected with the CPDA association process in the LC phase. The effect of camphor-containing chiral dopants of various structures on nematic LCs was compared. The values of the permittivity and birefringence components of the CPDA solutions in CB-2 were measured experimentally. A strong effect of this dopant on the anisotropic physical properties of the induced chiral nematic was established. A significant decrease in the dielectric anisotropy was associated with the 3D compensation of the LC dipoles during the formation of the helix. Full article

Methylthio moiety was observed to alter the mesomorphic features of rod-like Schiff-base-derived liquid crystalline materials. For this purpose, a new series of (E)-4-(alkoxy)-N-(4-(methylthio)benzylidene)aniline (I_n) liquid crystals were synthesized and examined using experimental and computational approaches. The compounds in the series differ from each other in the terminal alkoxy chain length that is attached to one end of the aromatic core. Various spectroscopic methods were used to verify the molecular structures of the produced derivatives. All compounds were checked for correct chemical structures using elemental analysis, FT-IR, ¹H-NMR, and ¹³C-NMR. Both a polarized optical microscope (POM) and a differential scanning calorimeter (DSC) were used in order to study the behavior of liquid crystals. Both tested compounds I₆ and I₈ have monotropic nematogenic properties while the longer chain derivative I₁₆ shows non-mesomorphic behavior. Computational studies were carried out using density functional theory (DFT) calculations to validate the experimental results. All of the analyzed compounds had their reactivity characteristics, dipole moments, and polarizability explained. Finally, in order to determine the chemical shape–mesomorphic property relationship, the present examined series was compared to other structurally comparable homologues. Full article

In recent years, metal biomaterials have emerged one after another, and have many excellent properties, playing a great role in medicine. However, these coatings cannot meet the medical needs in every aspect. Schiff base is an important organic synthetic reagent and liquid crystal material in organic chemistry. It mainly refers to a class of organic compounds containing imine or azomethine characteristic groups (-RC=N-). It has important anti-tumor, anti-virus, antifungal and antibacterial activities. Based on the excellent properties of Schiff base, the coatings made of Schiff base can improve the bioactivity of materials, which have a good development prospect in medicine. In this paper, the preparation methods and properties of Schiff base and many advantages of Schiff base coatings are reviewed. The research on the modification of coatings or functional membranes by Schiff base and Schiff base reaction, as well as the extensive application of special Schiff base coatings in many fields such as anti-corrosion, antibacterial, flame retardant, etc., are carried out. Suggestions for further research on Schiff base coatings on metal biomaterials are put forward. Full article

In this paper, preferential enrichment (PE) is described for three pairs of novel amino acid Schiff base Cu(II)/Cu(I) complexes. Single crystal X-ray diffraction indicated that 1-S/R are one-dimensional coordination polymers (CPs) with helical structures, and 2-S/R and 3-S/R are one-dimensional CPs with auxiliary ligands. By tuning the pH, the solvent and second ligands, the 1-S/R, 3-S/R underwent polymorphic transitions, resulting in enantioselective liberation of excess enantiomers into solution, until the deposited crystals were slightly enriched with the opposite enantiomer, thereby successfully exhibiting PE. However, under the effects of Cu(II), the solvent and low pH, 2-S/R did not exhibit PE and resulted in enrichment of racemic compounds, which was attributed to amino acid Schiff base chiral complex mechanisms of PE. The three pairs of Cu complex structures were characterized by UV-vis, MS and X-ray photoelectron spectroscopy (XPS). All chiral properties were studied by circular dichroism (CD) in the solid and liquid. Full article

Over the last decades, liquid crystalline has been of great recent importance due to many unique and different features. The linking unit, terminal group, and core system are the most factors to influence the liquid crystal behaviour. Schiff base linkage with the formula of -C=N- can maintain linearity by providing the stepped core structure with high stability. Incorporation of Schiff base linkage in cyclotriphosphazene system enhances the mesophase characteristic and high thermal stability. This review focussed on the mesophase behaviour and physical properties of cyclotriphosphaze derivatives attached to Schiff base linkages. A basic introduction to liquid crystalline materials, including description and classification, is provided in this review. Full article

A new liquid crystal series of pyridin-2-yl 4-[4-(alkylphenyl)iminomethyl]benzoate was synthesized and characterized for their mesomorphic behavior. These compounds contain Schiff base and carboxylate ester mesogenic cores, in addition to terminal alkyl chains with a different number of carbons. The structures were confirmed via FT-IR, and ¹H NMR spectroscopy. The phase transitions were studied by differential thermal analysis (DSC) and the mesophase types were identified by polarized optical microscopy (POM). A comparative study was performed between the synthesized compounds and previously reported compounds. Density functional theory (DFT) calculations were included in the study to compute the dipole moment and the polarizability, as well as the frontier molecular orbitals and the charge distribution mapping, which impact the terminal and lateral interactions of the compounds. The theoretical results were discussed to confirm the experimental data and explain the mesomorphic behavior of the compounds. Finally, the energy gap, global softness, and chemical hardness were calculated to determine the suitability of the liquid crystalline compounds to be employed in applications. Full article

The Fe(III) complexes of branched asymmetric dendrimers were obtained by a one-step reaction as the second-generation architectures. Mesomorphic behavior was found for complexes with PF₆⁻ and BF₄⁻ counter-ions. To obtain knowledge about the existence of HS and LS fractions of iron(III) ion and their evolution with temperature, EPR methods were used. It was demonstrated that compounds contain one low-spin (LS, S = 1/2) and two HS-spin (HS, S = 5/2) of Fe(III) centers and are packed into two magnetic sub-lattices. A floating layers of Fe(III) complexes and Langmuir–Blodgett films on their base were formed and investigated in the presence of a magnetic field. Full article

Three rings 2-hydroxypyridine liquid crystalline compounds have been prepared and fully characterized. The mesomorphic behavior of the prepared compounds has been investigated in terms of differential scanning calorimetry (DSC) and polarized optical microscopy (POM). Moreover, a comparative study between the prepared compounds and previously reported analogs has been discussed in terms of the orientation and position of the mesogenic core, in addition to the direction of the terminal alkyl chains. Furthermore, a detailed computational approach has been studied to illustrate the effect of geometrical and dimensional parameters on the type of the enhanced texture and the mesomorphic range and stability. The results of the DFT study revealed that the orientation of the mesogen could affect the mesomorphic behavior and this has been attributed in terms of the degree of the polarizability of the linking groups. This result has been confirmed by calculation of the net dipole moment and the molecular electrostatic potential that show how the mesogen orientation and position could impact the molecular charge separation. Finally, the effect of the pyridyl group has been also investigated in terms of the calculated aromaticity index and the π-π stacking. Full article

Supramolecular, low-melting (near or below 0.0 °C) ionic liquid crystals with two rings of Schiff bases were prepared and studied. The Schiff bases were synthesized using 4-substituted aniline derivatives and 4-pyridine carbaldehyde and then mixed in equimolar amounts with linear 1-bromoalkanes of different chain lengths, namely C6, C8, and C14. The mesomorphic behavior and thermal properties of the compounds were determined by polarized optical microscopy (POM) and differential scanning calorimetry (DSC). Only the ionic liquids analogous with 1-bromotetradecane exhibit mesomorphic behavior. All, except the smectic A (SmA) monomorphic fluorine-substituted complex, show dimorphic enantiotropic mesophases, namely SmA followed by nematic (N) mesophases depending on the temperature rise. The DSC and POM results for the induced mesophases were then treated with density functional theory calculations (DFT). The results showed that both the polarity of the polar groups and the length of the alkyl groups strongly influence the mesomorphic properties of the ionic liquids. Full article

A homologous set of liquid crystalline materials (Tn) bearing Schiff base/ester linkages were prepared and investigated via experimental and theoretical techniques. Terminal flexible groups of different chain lengths were connected to the end of phenylbenzoate unit while the other end of molecules was attached to the heterocyclic pyridine moiety. The molecular structures of the designed molecules were evaluated by FT-IR, NMR spectroscopic analyses, whereas their mesomorphic properties were investigated by polarized optical microscopy (POM) and differential scanning calorimetry (DSC). They all exhibited dimorphic properties with the exception of the members having the shortest and longest terminal flexible chains (n = 6 and 16), which were monomorphic. The T16 derivative was further found possessing purely smectic A (SmA) mesophase while others have their lengths covered by nematic (N) phase. Moreover, the computational evaluation of the azomethine derivatives was carried out using a DFT approach. The polarity of the investigated derivatives was predicted to be appreciably sensitive to the size of the system. Furthermore, the Frontier molecular orbitals analysis revealed various distributions of electron clouds at HOMO and LUMO levels. Full article

A series of non-symmetrical Schiff base liquid crystals were prepared and investigated. Schiff bases of p-alkyloxy aniline derivatives and 4-phenyl pyridine-4′-carbaldehyde were synthesized. The terminal alkoxy groups substituting aniline are of varied chain length, namely C6, C8, and C16. The structures of the compounds were confirmed via ¹H NMR and ¹³C NMR spectroscopy. Different mesophases of the samples were thermally and optically characterized by differential thermal analysis (DSC) and polarized optical microscopy (POM). All samples revealed enantiotropic smectic B (SmB) and smectic A (SmA) mesophases. The results obtained were further correlated with the density functional theory (DFT) theoretical calculations. The results are compared to a series of compounds bearing biphenyl moiety in their mesogens. The thermal stabilities of the different mesophase reduced upon the increment of the alkoxy chain length. The temperature ranges of both the smectic mesophases of new compounds bearing the 4-phenyl pyridine moiety are generally expanded higher than the other series. In addition, the total mesophase range is greater in the new compounds when compared to their biphenyl analogues. The DFT results were investigated in terms of the molecular geometries and the frontier molecular orbitals as well as the charge distribution mapping to show and illustrate the difference in the mesomorphic properties. Full article