Synthesis and characterization of some novel liquid crystalline compounds of 1,3,4-oxadiazoline and their hydrazone derivatives

Three new series of mesogens have been synthesized by fixing 4-methoxy or 4-butoxy substituted phenyl ring in one side and 4-hydroxy, bromo or amino substituted phenyl group in the other side with different central linkage. The molecular structure of these series was confirmed by elemental analysis and FTIR and ¹HNMR spectroscopy. The mesomorphic properties were studied by using differential scanning calorimetry (DSC) and optical polarizing microscopy (OPM). All the compounds of series [I] exhibit enantiotropic smectic B (SmB) phase. All the compounds of series [II] and [III] display SmB and nematic (N) phases. The mesomorphic properties were found to be dependent on the two terminal 4-substituted phenyl groups and the central linkage group.     

Synthesis and Mesomorphic Properties of New Columnar Liquid Crystal Containing 1,3,5-triiminebenzene with Pendant 1,3,4-thiadiazole Group

A novel discotic liquid crystal series based on 1,3,5-benzenetrisazomethine derivatives with three pendant 2-amino-5-(4′-n-alkoxy)phenyl-1,3,4-thiadiazole has been synthesized, which is the first columnar molecules containing 1,3,4-thiadiazole moiety exhibiting a discotic liquid crystal. The molecular structure of compounds was confirmed by FT-IR, ¹H-NMR, and mass spectroscopy and elemental analysis. The electron excitation properties of these compounds were investigated by UV-vis absorption spectroscopy. Their liquid crystalline properties were studied by polarizing optical microscopy and differential scanning calorimetry. The formation of a columnar mesophase was found to be dependent on the number of methylene unit in alkoxy side chains.     

Synthesis,crystal and molecular structure,and infrared characterization of two amino derivatives of 1,3,4-thiadiazole

2-amino-5-methyl-1,3,4-thiadiazole, 2-arnino-5-methyl-3H-1,3,4-thiadiazolium bromide[(amtzH)(amtz)Br] and bis (2,5-diamino-3H-1,3,4-thiadiazolium) sulphate [(a ₂ tzH)₂SO₄] were prepared and characterized by means of X-ray structural analysis and infrared spectroscopy. The crystals of (amtzH) (amtz)Br are monoclinic; space groupP2₁/c, witha=7.620(2),b=17.166(2),c=9.411(2)Å,=96.34(2)°, andZ=4. Its asymmetric unit contains one protonatedamtzH cation, one neutralamtz molecule, and one bromide ion. The crystals of (a ₂ tzH)₂SO₄ are monoclinic; space groupC2/c, witha=11.797(2),b=9.213(2),c=10.720(2)Å,=91.30(2)°, andZ=4. The structure is built up of one crystallographically independenta ₂ tzH cation and one half sulphate ion with crystallographically dictated twofold symmetry.     

Synthesis and characterization of new nematic liquid crystalline compounds-based thiophene units

Four new liquid crystalline thiophene compounds (M1?M4) with a long flexible spacer were prepared. Their structures were characterized by Fourier transform infrared and proton nuclear magnetic resonance. The mesomorphism and thermal stability were investigated with differential scanning calorimetry, polarizing optical microscopy, and thermogravimetric analysis. The photo-physical properties were evaluated using ultraviolet/visible spectroscopy and photoluminescence. M1?M4 all showed thermotropic mesogenic properties with excellent thermal stability, and exhibited nematic threaded texture, droplet texture, and Schlieren texture on heating and cooling cycles. The effect of flexible spacer and terminal groups on mesomorphic and spectroscopic property is discussed. The experimental results demonstrated that the tendency toward melting temperature (Tm) decreased, while isotropic temperature (Ti) increased with increasing the flexible spacer length. In CHCl₃ solution, these thiophene compounds displayed an intense broad absorption band peaking within 230–340 nm and a maximum fluorescent emission wavelength at 426–439 nm.     

Substituent and solvent effects on UV‐visible absorption spectra of liquid crystalline disubstituted biphenylcyclohexane derivatives – a computational approach

A computational approach has been carried out on liquid crystalline disubstituted biphenylcyclohexanes (BCHs) of general formula R‐C₆H₁₀‐C₆H₄‐C₆H₄‐X with R: C₃H₇; X: H (BCH30) and R: C₅H₁₁; X: CN (BCH5CN) using the CNDO/S + CI and INDO/S + CI methods. These methods have been employed to calculate and analyze the spectral shifts, and absorbance measurements in UV‐visible range of the systems. The electronic transitions, absorption wavelength, HOMO (Highest Occupied Molecular Orbital), and LUMO (Lowest Unoccupied Molecular Orbital) energies have been calculated. Further, ultraviolet (UV) stability of the molecules has been discussed in the light of absorption wavelength and electronic transition oscillator strength (f). The effect of different solvent media and substituents on transition energies, oscillator strength, and other absorption parameters has also been reported. The present article provides valuable information regarding enhancing the UV stability of molecules by marinating their conductivity. Further, these absorption spectra will provide valuable data base for future computational studies, and the other experimental investigations. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Synthesis of liquid crystals based on hydrogen-bonding of 4-(Octyloxy)benzoic acid with 4-alkylbenzoic acids

A molecular recognition process has been used to form new mesogenic molecular structures, where intermolecular hydrogen bonding occurs between 4-(octyloxy)benzoic acid (8BAO) and four 4-alkylbenzoic acids (nBAs, n = 2, 5, 6, 7). The synthesis of these complexes has been attained by resorting to mechanochemistry. The resulting materials have been characterized by polarizing optical thermal microscopy, differential scanning calorimetry, vibrational spectroscopy, X-ray powder diffraction, and ¹H NMR relaxometry. All the elements of the series show the formation of a mesophase. For one of the complexes, its electro-optical properties have also been assessed, resulting comparable to those of other widely used liquid crystals.     

Design,synthesis and characterization of hydrogen bonded thermotropic liquid crystals

A homologous series of seven linear hydrogen bonded thermotropic liquid crystals are isolated from p-n-octyloxy benzoic acid (8BAO) and p-n alkyl benzoic acids (nBA, where n varies from 2 to 8). In all the seven complexes, hydrogen bonding is a result of complementary proton-donor and electron-acceptor pairs derived from carboxylic acids of 8BAO and nBA. Spectroscopic characterization such as Fourier Transform Infrared spectroscopy (FTIR) and Nuclear Magnetic Resonance (¹HNMR, ¹³CNMR) are performed for all the seven complexes to confirm the intermolecular hydrogen bonding and the nature of chemical environment respectively. Seven mesogen are examined by Polarizing Optical Microscope (POM) for identification of the phase polymorphism through standard textures. Transition temperatures and corresponding enthalpy values of the individual mesogenic phases are experimentally obtained from the analysis of the respective Differential Scanning Calorimetry (DSC) thermograms. Phase diagram of this homologous series is constructed based on the data of transition temperatures, further qualitative analysis of the phase abundance is discussed. Thermal stability factor for each of the mesogenic phase has been determined. Order of phase transition is experimentally obtained by Navard and Cox technique. Specific heat for each phase transition of individual complexes is derived from the DSC data. Change of color of the texture with temperature in the same phase is referred as parachromatism and is observed in nematic phase of two mesogens.     

Design,synthesis and characterization of hydrogen bonded liquid crystals formed between methyl malonic acid and p-n-alkyloxy/alkyl benzoic acids

Two novel homologous series of hydrogen bonded liquid crystals (HBLC) comprising of 14 mesogens are formed between Methyl Malonic acid (MM) and p-n-alkyloxy/alkyl benzoic acids (nBAO/nBA). FTIR study confirms the formation of hydrogen bond. Phases exhibited by these mesogens are characterized by optical textural studies and Differential Scanning Calorimetry (DSC) studies. Phase diagram is constructed from these studies. Other thermal parameters such as order of the transition, thermal stability factor and specific heat are also elucidated. Optical tilt angle measurement and optical filtering action are also carried out. The influence of oxygen atom is also discussed.     

Synthesis,structure, and mesomorphism of novel liquid crystalline acrylate monomers and polymers

A series of novel liquid crystalline monomers (M₁?M₈) and side chain polymers base polyacrylate backbone were synthesized. The chemical structures were characterized by FT-IR and ¹H-NMR spectra. The mesomorphism and thermal behavior was investigated by polarizing optical microscopy, differential scanning calorimetry, and thermogravimetric analysis. The relationships of structure and mesomorphism are discussed in detail. The eight monomers and their corresponding polymers all show enantiotropic nematic phase. With increasing the spacer length or flexibility of the terminal group, the melting temperature (T_m) and isotropic temperature (T_i) of the corresponding monomers and polymers all decreased. However, with increasing the rigidity of the mesogenic core, T_m and T_i of the corresponding monomers and polymers all increased. TGA showed that all the polymers obtained in this study had excellent thermal stability.     

Synthesis,characterization, and mesomorphic investigations of diester-substituted salicylaldimines and their copper (II) complexes

A novel homologous series of N-[4-[4′-n-alkoxy)benzoyloxy-2-hydroxybenzylidene)-4-carbethoxy anilines, H_2n+1C_nOC₆H₄C(O)OC₆H₃(OH)C(H)?NC₆H₄COOC₂H₅ (n = 6, 8, 10, 12, 14, 16) and their copper(II) complexes have been synthesized. All these compounds have been characterized by suitable spectroscopic techniques. The mesomorphic properties of these compounds were investigated by differential scanning calorimetry (DSC) and polarizing optical microscopy (POM). The ligands exhibit wide range of enantiotropic smectic A and nematic phases as confirmed by their typical optical texture under polarizing microscope. The square planar copper(II) complexes of the ligands show only an isotropic phase at higher temperature and no mesogenic nature is observed. DFT calculations have been performed using GAUSSIAN-03 program at B3LYP level to obtain the stable electronic structure of the ligand with decyloxy chain length and its copper(II) complex.     

A new supramolecular cocrystal of 2-amino-3-bromopyridine with 4-methylbenzoic acid: Synthesis,structural, spectroscopic characterization and comparative theoretical studies

The 1:1 cocrystal of 2-amino-3-bromopyridine (2A3BP) with 4-methylbenzoic acid (4MBA) has been prepared by slow evaporation method in methanol, which was crystallized in monoclinic P2₁/c space group having two molecules in the asymmetric unit. The cocrystal has been characterized by single crystal X-ray analysis, FTIR, ¹H NMR, ¹³C NMR, and Powder XRD. Theoretical investigations have been calculated by HF and density function (B3LYP) method with the 6-311+G(d,p) basis set. The vibrational frequencies together with the ¹H NMR and ¹³C NMR chemical shifts have been calculated on the fully optimized geometry of 1. Theoretical calculations of bond parameters, harmonic vibration frequencies, and isotropic chemical shifts are in good agreement with the experimental results. Solvent-free formation of these cocrystal was confirmed by powder X-ray diffraction analysis. The crystal structure was stabilized by N_pyridine—H···O = C, C = O—H···N_pyridine and C—H···Br hydrogen bonding interactions.     

Synthesis and characterization of tetraprolinium silicotungstic acid tetra‐hydrate,a new organic‐inorganic hybrid based on polyoxometallates

A new solvated polyoxometallate bearing an amino acid, ( I ), has been prepared for the first time by the reaction of 0.16 mmol α‐H₄SiW₁₂O₄₀.15H₂O with 0.78 mmol of L‐proline in hydrochloric acid at pH 3. The structure of ( I ) was substantially characterized by some physical approaches, such as elemental analysis, infrared spectroscopy, and ¹H‐NMR. Our findings proved that ( I ) could be formulated as [L‐C₅H₁₀NO₂]₄[SiW₁₂O₄₀].4H₂O. It is believed that the electrostatic attractions and hydrogen bonding between tungstosilisic acid and the prolinium cation affected the structure of ( I ). It is evident that the polyoxometallates moieties were arranged in good order to form large holes in the structural backbone. These cavities were occupied by the prolinium cations and water molecules. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)