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Relevant academic research and scientific papers

Synthesis and properties of Schiff's bases derived from 1,3,4-thiadiazole as a mesogenic unit

Some new liquid crystalline 2,5-disubstituted 1,3,4-thiadiazole derivatives incorporating a central group (-CH=N-) have been synthesized by treating 2-amino-5-(4-alkoxyphenyl)-1,3,4-thiadiazole with corresponding p-alkoxybenzaldehyde. Their structures have been characterized with Elementary Analysis, IR, 1HNMR and MS, and their properties were determined by using DSC and Texture. All 12 compounds are enantiotropic liquid crystals, and most of them exhibit nematic mesomorphism and broad smectic C mesomorphic ranges. Several compounds show only the smectic C mesophase. By introducing an -OH group into the phenyl ring the thermal stability of the mesophases increases due to the formation of a hydrogen bond.

Influence of the lanthanide contraction on the transition temperatures of rare-earth containing metallomesogens with Schiff base ligands

We have synthesised liquid-crystalline rare-earth complexes with Schiff base ligands. The stoichiometry of these complexes is Ln(LH)3(NO3)3, where Ln is a trivalent rare-earth ion (Y3+, La3+-Lu3+

The influence of molecular flexibility on the mesogenic behavior of a new homologous series based on azo-azomethine: Synthesis, characterization, photoisomerization and DFT study

Through condensation of 2-hydroxy-4-n-alkoxybenzaldehyde (n = 2 to 8, 10, 12, 14, 16, 18) with (E)-4-((2,4-dimethylphenyl)diazenyl) benzene-1,3-diamine, new homologous series of rod shaped calamite liquid crystals based on azo-azomethine have been prepared. All synthesized compounds were characterized by FT-IR, 1H NMR, and 13C NMR spectroscopy. Use Differential Scanning Calorimeter (DSC) and Polarizing Optical Microscope (POM) to check the liquid crystal properties of all synthetic compounds. In the homologous series, all the compounds are mesogenic; some of them are in the nematic phase; some of them appear in the smectic A phase, and some appear in the nematic and smectic A phases. UV–vis pectroscopy was used to study the photoisomerization in chloroform. DFT (Density functional theory) level calculations and complete geometric optimization of all synthetic compounds are performed using B3LYP/6-31+G (d, p) basis sets.

Synthesis, characterization, and mesomorphic properties of some new Schiff base homologues series and their Cu(II) complexes

In present study, we have synthesized two homologous series of some new Schiff base of 4-n-alkoxy-2-hydroxy benzaldehyde (n = 2–8, 10, 12, 14, 16, 18) with 4-amino acetanilide and their corresponding Cu(II) complexes. A series of new Schiff base containing two aromatic rings have been synthesized and characterized by various spectroanalytical techniques including FT-IR and 1H NMR. The mesomorphic properties of these compounds were observed by optical polarized light microscopy (POM) and confirmed by differential scanning calorimetry (DSC) study. It has been observed that all the newly synthesized compounds exhibit wide range SmA phase.

Polarization effect in luminescent mesogenic BF2 complexes derived from heterocyclic benzothiazoles

Two series of benzo(thia)xazoles 1–2 and one series of boron difluoride complexes 2-BF2 derived from benzothiazoles 2 were reported, and their mesomorphic and optical properties were investigated. The crystal and molecular structures of compound 2 and 2-BF2 (all n = 8) were determined by means of X?ray structural analysis, and both crystallize in the triclinic P-1 and monoclinic P21/c. The geometry at boron center is perfectly tetrahedral, and the overall molecular shapes are considered as rod?shape. Both benzo(thia)xazoles 1 and 2 exhibited N or/and SmC phase, and boron complexes 2-BF2 formed N or/and SmC phase. Benzothiazoles 2 showed a much wider temperature range of mesophase than those of benzoxazoles 1, which were attributed to the better polarization by sulfur atom incorporated. Boron complexes 2-BF2 (n = 10, 12) emitted a yellow?to?green emission at λmax = 569–571 nm in CH2Cl2. This is the first mesogenic BF2 complexes derived from benzothiazoles.

Development of nematic and orthogonal smectic phases in short-core fluorinated hockey-stick shaped liquid crystal compounds

Here we report synthesis and investigations on novel short-core hockey-stick shaped molecules bearing a 4-n-alkyloxy-2-hydroxybenzylidene moiety at one end and polar fluoro-biphenyl moiety at the other end. The polar chloro and fluoro substituent at the lateral position of the core confers nematic and orthogonal smectic mesomorphism. The mesophase morphology is characterized by polarizing optical microscopy (POM), differential scanning calorimetry (DSC), X-ray diffraction (XRD), electro-optical study and dielectric spectroscopy. The fluorinated compounds 1b (n = 16) and 1c (n = 18) have long terminal hydrocarbon tail and show orthogonal smectic phases with antiferroelectric switching behaviour. The chlorinated compound 2e (n = 8) with relatively short terminal chain length exhibits only a monotropic nematic phase on cooling. The nematic phase is comprised of cybotactic clusters as confirmed by XRD and exhibits electro-optic switching. The compound 2i (n = 12) manifests a short range enantiotropic nematic and additional orthogonal smectic phase. Dielectric spectroscopy reveals polar correlations in the nematic and smectic phases.

Chiral Bent-Shaped Molecules Exhibiting Unusually Wide Range of Blue Liquid-Crystalline Phases and Multistimuli-Responsive Behavior

Recently, an unprecedented observation of polar order, thermochromic behavior, and exotic mesophases in new chiral, bent-shaped systems with a ?CH3 moiety placed at the transverse position of the central core was reported. Herein, a homologous series of compounds with even-numbered carbon chains from n=4 to 18 were synthesized, in which ?Cl was substituted for ?CH3 at the kink position and a drastic modification in the phase structure of the bent-shaped molecule was observed. An unusual stabilization of the cubic blue phase (BP) over a wide range of 16.4 °C has been witnessed. Two homologues in this series (1-12 and 1-14) exhibit an interesting phase sequence consisting of BPI/II, chiral nematic, twist grain boundary, smectic A, and smectic X (SmX) phases. The higher homologues (1-16 and 1-18) stabilize the SmX phase enantiotropically over the entire temperature range. Crystal structure analysis confirmed the bent molecular architecture, with a bent angle of 148°, and revealed the presence of two different molecular conformations in an asymmetric unit of compound 1-4. A DFT study corroborated that the ?Cl moiety at the central core of the molecule led to an increase in the dipole moment along the transverse direction, which, in turn, facilitated the unusual stabilization of frustrated structures. Crystal polymorphism has been evidenced in three homologues (1-10, 1-12, and 1-14) of the series. On the application of mechanical pressure through grinding, compound 1-10 transformed from a bright yellow crystalline solid to a dark orange–green amorphous solid, which reversed upon dropwise addition of dichloromethane, indicating reversible mechanochromism in this class of compounds. In addition, excellent thermochromic behavior has been observed for compound 1-10 with a controlled temperature–color combination.

Schiff base of 4-n-alkoxy-2-hydroxy benzaldehyde with 4-amino acetophenone and their Cu(II) complexes: synthesis, characterization and mesomorphic behavior

New homologous series of Schiff’s base of 4-n-Alkoxy-2-hydroxy benzaldehyde (n = 2 to 8, 10, 12, 14, 16, 18) with 4-amino acetophenone and their Cu(II) metal complexes have been synthesized. The compounds were characterized using various spectroscopic techniques including FT-IR, 1H-NMR, 13C-NMR. Mesomorphic properties of these compounds have been investigated with polarizing optical microscope and differential scanning calorimeter. These compounds exhibit wide range SmA phase as confirmed by their typical optical texture under polarizing microscope.

Choline hydroxide: An efficient and biodegradable catalyst for the synthesis of 2-amino-3-nitro-4H-chromene derivatives in an aqueous medium

An expedient, eco-friendly and efficient procedure for the synthesis of novel 2-amino-3-nitro-4H-chromene derivatives has been developed through the reaction of various 2-hydroxybenzaldehydes and (E)-N-methyl-1-(methylthio)-2-nitroethenamine in the presence of the basic ionic liquid catalyst (choline hydroxide (ChOH)) at room temperature an aqueous medium. The advantageous of this method is a biodegradable and recyclable catalyst, mild, environmentally friendly and high products yields (83-96%) in short reaction times.

Luminescent mesogenic borondifluoride complexes with the Schiff bases containing salicylideneamines and β-enaminoketones core systems

Three new families of borondifluoride complexes 1a–c derived from salicylideneamines 2a and β-enaminoketonates 2b–c were reported, and their mesomorphic and optical properties were also investigated. One single crystal and molecular structure of nonmesogenic BF2 complex 1c (n = 10) was resolved and the geometry of the central boron atom was tetrahedron. A larger dihedral angle of 81.3° between the two phenyl rings observed in crystal lattice was attributed to the lack of liquid crystallinity. Boron complexes 1a formed monotropic SmA phases, while boron complexes 1b exhibited enantiotropic SmC mesophases. The optical property of the boron complexes was dependent on their molecular structures, and they emitted a blue–to–green emission at λmax = 476–541 nm in the solution and 488–550 nm in the solid state. This is the first group of mesogenic BF2 complexes with the Schiff bases derived from respective salicylideneamines and β-enaminoketones.