The Smectic Phase of p. p'-di-n-Heptylazoybenzene: A 1H NMR study of Its Anisotropy of Diamagnetic Susceptibility and of Its Use for Measuring Proton Chemical Shift Anisotropies

Abstract

The anisotropy of the diamagnetic susceptibility of the smectic liquid crystal p,p'-di-nheptylazoxybenzene (HAB) has been measured by use of ¹H NMR. The value of (X‖ - X⊥) is found as e.g. 1.418. 10^?6 at 318 K. Furthermore, we have observed local solvent effects of HAB on dissolved globular molecules, which are of the order of 0.10 to 0.19 ppm for methane, 0.37 to 0.44 ppm for tetramethylsilane, 0.35 to 0.40 ppm for tetramethylstannane, and 0.39 to 0.41 ppm for neopentane. These values are dependent on temperature and may lead to large uncertainties in the determination of proton chemical shift anisotropics. A theoretical treatment of the magnetic fields in the annulus of a double-wall tube and inside the inner tube filled with a smectic liquid crystal and variable angle between the applied field and the optic axis is also given.     

Phase Diagram and Dielectric Studies in Hydrogen-Bonded Liquid Crystal System

The thermal and dielectric behaviors of mixtures were investigated for systems of p-n-hexyloxybenzoic acid (6OBA) and p-n-octyloxybenzoic acid (8OBA) by differential scanning calorimetry, polarized optical microscopy, and dielectric measurements. The T-X phase diagram was obtained for this system. Eutectic composition was calculated and received experimentally. Enthalpies of mixing were calculated to describe phase transitions physically. All mixtures show enantiotropic smectic and nematic phases. Dielectric permittivity has higher value for the mixture with fractional proportion of 30 to 70% mol for 8OBA than that for initial acid. It is assumed that co-crystallization of initial compound occurs when the ratio of components is close to equimolar ratio.     

A Direct Observation of the Switch-Over Transition in Mixed Liquid Crystals of Opposite Diamagnetic Anisotropies

From deuteron NMR studies of pure mixed liquid crystals of opposite diamagnetic anisotropies, a direct observation of the switch-over transition is reported. At the critical concentration and temperature, two spectra corresponding to two different orientations are observed. No noticeable change in the optical properties was observed around the critical point. At the critical concentration, the higher temperature corresponds' to the orientation similar to that for the system with positive diamagnetic anisotropy in all the cases investigated.     

Crystal structure and intermolecular coordination behavior of a porphyrin bearing a hydroquinone receptor, meso-mono(hydroquinonyl) triphenylporphyrinatozinc

The structure of a porphyrin bearing a hydroquinone receptor unit, meso-mono(hydroquinonyl)triphenylporphyrinatozinc (1), is reported. The compound crystallizes from benzene in the monoclinic space group P2₁/c(#14) with a = 10.896(2) Å, b = 15.674(4) Å, c = 12.564(3) Å, = 102.04(2)° and d _calc= 1.368 g/cm³ for Z = 2. The unit cell has two porphyrins and four benzene solvates. The structural study reveals no self-assembled aggregates due to intermolecular coordination of the hydroxy groups of the hydroquinone to the zinc ion in the porphyrin cavity, an observation that agrees with the results of ¹H NMR studies performed in benzene-d₆ solutions. On the contrary, the ¹H NMR results in CDCl₃ indicate the existence of self-assembled aggregates.     

Synthesis,characterization of new carboxylic acid derivatives bearing 1,3,4-thiadiazole moiety and study their liquid crystalline behaviors

Thirteen carboxylic acid derivatives containing 1,3,4-thiadiazole ring in their core and swinging alkoxy terminal were synthesized. They were characterized by ¹H, ¹³C NMR spectroscopy, FTIR, and mass spectrometry. Their liquid crystalline behaviors have been studied by differential scanning calorimetry (DSC) and polarized optical microscopy (POM). The 1,3,4-thiadiazole compounds in this study were 2,5 di-substituted asymmetrical, alkoxy, and carboxy linkages. The compounds with alkoxy of long carbon chains (n > 7) displayed Smectic C phase. The liquid crystal properties were found to be affected by the length of alkoxy chain attached to the phenyl moiety and the two types of the dimeric form were resulted from the hydrogen bonding interaction between carboxylic acid molecules.     

Comparison of Response of Biological Supermacromolecules to Magnetic Field Depending on Surface Structure

Abstract

By using time-resolved synchrotron radiation X-ray scattering technique we have observed behaviors of biological supermacromolecules in solutions under magnetic field. Here we treated two different supermacromolecules, namely, tobacco mosaic virus and cucumber green mottle mosaic virus. Both viruses take isomorphous cylindrical structures regarded as a typical rod-shaped colloidal particle. Although these viruses are closely related genetically and take isomorphous structures, we found a quite different behavior between those suspensions under magnetic field. The secondary and tertiary structures of the coat proteins of these viruses are mostly identical with each other. There exists a minor difference in the protein surface structures. The present results suggest that the response of the supermacromolecular assembly to magnetic field depends not only on the diamagnetic anisotropy but also on the surface structure.     

Effect of reversible photostructural change on the polarization of photoluminescence in chalcogenide glasses

Optical absorption edge in annealed As₂S₃ films shifts to lower energy after band-gap illumination. In these photodarkened films, polarization memory of photoluminescence was found to increase. In the case of illumination with linearly polarized light, anisotropy is induced in the absorption edge. The polarization memory was larger for larger shift of absorption edge. In contrast with this trend, the memory was smaller in As-rich films, the absorption edge of which was located at lower energy. It is considered that the optical anisotropy of the luminescence centers increases accompanying the reversible photostructural change.     

Linear optical properties and Raman spectroscopy of natural fluorapatite

Precision refractive indices and their dispersion in the visible and near IR range (430 – 2400 nm) and thermal expansion (including its anisotropy and temperature dependence between 144 K and 673 K) were determined for gem‐quality crystals of fluorapatite from Durango, Mexico. In addition, results of a polarized Raman spectroscopy study on these crystals are given. Fluorapatite crystals show moderate values of thermal expansion with small anisotropy. The linear optical properties of the crystals allow no phase matching for third harmonic generation, but signalize, together with the Raman characteristics, a potential suitability of fluorapatite as nonlinear optical material for χ⁽³⁾‐based stimulated Raman scattering.     

Oxygen and hydrogen profiles and electrical properties of unintentionally doped gallium nitride grown by hydride vapor phase epitaxy

Commercially available hydride vapor phase epitaxy gallium nitride (GaN) is characterized with the aim to correlate the oxygen and hydrogen secondary ion mass spectrometry profiles of a GaN wafer with the electrical properties of the sample. A GaN layer model, including doping profile and mobility, is derived, utilizing electrical (capacitance–voltage, Hall), structural (high resolution X‐ray diffraction) and optical (polarized infrared spectroscopy) methods. Oxygen and hydrogen are easily incorporated during hydride vapor phase epitaxy growth of GaN. Oxygen is an n‐type dopant in GaN, whereas hydrogen may passivate some of the donors. Electrical and optical properties correlate with a low defect concentration top GaN layer and a high defect concentration GaN interlayer.     

Dielectric Anisotropy and the Order Parameter of HXBBA

Abstract

Measurements of dielectric anisotropy (Δ?), refractive indices (n _e , n _o), birefringence (Δn) and density (ρ) have been made in the nematic and smectic phases of N(-p-hexyloxybenzylidene)-p-butylaniline (HXBBA). The results indicate that the various transitions are of the first order type except smectic B-smectic G, which may be a second order transition. The order parameter S has been determined using the isotropic internal field model (Vuks approach) and the anisotropic internal field model (Neugebauer's approach) and both the values agree fairly well. The dielectric anisotropy (Δ?) increases strongly in the smectic phases whle S increases only slowly. It is interpreted by an increase of dipole-dipole correlations.     

Diamagnetic Anisotropy Measurements of Nematic Liquid Crystals

Electro-optic effect of liquid crystals in the presence of a magnetic field was investigated. Two independent techniques: magnetic field dependent threshold voltage and magnetic field-assisted relaxation time, were used to evaluate the diamagnetic anisotropy for three nematic liquid crystals: BDH-E7, RO-TN-103 and ZLI-1132. Correlation between the diamagnetic anisotropy and the molecular structures was obtained. This information is particularly important for synthesizing liquid crystal components with desired diamagnetic anisotropy.     

Synthesis and Mesomorphic Characterisation of Chiral Homologues

Abstract

Chiral liquid crystals have attracted considerable interest as they exhibit a good variety of modulated phases. We have synthesised a homologous series viz., 4-(4^!-n-alkoxy benzoyloxy) benzylidene-4^!!?1-(s)-methyl propoxy anilines, incorporating a terminal chiral centre, inorder to obtain better understanding of the relationship between molecular structure and appearance of SmC* phase in the molecules. It is observed that, in the present series the lower members upto butyl are pure nematogens, while pentyl to hexadecyl derivatives exhibit classical smectic as well as nematic mesophases. An additional smectic C* phase is observed in the middle octyl to dodecyl homologues. The homologues have been characterised by IR, NMR and DSC. Their mesomorphic properties have been compared with structurally related homologous series.     

Synthesis,spectral, X-ray diffraction and DFT studies on 1-(2-methyl-2-propenyl)-3-(2,3,4,5,6-pentamethylbenzyl)benzimidazolium chloride hydrate

A new benzimidazole based N-heterocyclic carbene (NHC) salt (1) was synthesized by the reaction of benzimidazole precursor with alkyl halide. The structure of 1 was determined by elemental analysis, FT-IR, ¹H NMR and ¹³C NMR spectroscopy tecniques and X-ray crystallography. The compound crystallized in the triclinic space group P-1 with two molecules in the unit cell. The optimization of 1 was firstly performed at B3LYP/6-311G++(d,p) level, then the theoretical spectral studies performed and compared with the experimental values. Besides the frontier molecular orbital energies and chemical reactivity analysis of 1, together with the electrostatic potential and molecular electrostatic potential analyses were performed at the same level of theory.     

Photo-Controllable Rotation of Cholesteric Double-Twist Cylinders

Abstract

We fabricated aggregates of cholesteric cylinders coexisting with the isotropic phase and investigated their dynamics under a temperature gradient. Each constituent cylinder possessed the double-twist (DT) structure, and when a heat flux was applied, the whole aggregates rotated as a rigid-body without changing the DT orientation. The angular velocity was proportional to the heat flux and the rotational direction was determined by the molecular chirality and the flux direction. The result suggests that the rigid-body rotation was driven by the thermomechanical cross-correlation in chiral LCs. We also succeeded in switching the rotation by changing the illumination onto the sample.     

Development of Personal UV Biodosimeter Based on Vitamin D Photosynthesis

Abstract

A new approach to monitoring of vitamin D synthetic capacity of UV solar/artificial radiation is described. Nematic liquid crystal (LC) was converted into cholesteric phase by chiral dopant of 7-dehydrocholesterol (provitamin D₃), and the effects of UV irradiation were studied using spectral and polarized observations. Significant changes in optical characteristics of the LC films depending on UV exposure were observed as a result of UV initiated photoisomerization that changed helical twisting power of dopant molecules.     

Three Types of Behaviour of Multiwall Carbon Nanotubes in Reactions with Intercalating Agents

Abstract

Interaction between multiwall nanotubes and intercalating agents (K or FeCl₃) was studied using seven different nanotube materials. SEM, TEM, X-ray diffraction, Raman spectroscopy and other techniques were employed to study the reaction products. It was found that the reaction way is determined by nanotube structural type and that nanotubes may exhibit three types of reaction behaviour: intershell intercalation: no-reaction; and intercalation-assisted break-up.     

Interlayer Reaction of Polyamine/α-Zirconium Phosphate Intercalation Compounds with Some Aldehydes

Abstract

The intercalation compound between α-zirconium phosphate and N,N′-bis-(3-aminopropyl)-1, 3-propanediamine has two different modifications with respect to the conformation of the guest amine molecules: one is “bent form” and the other “straight form”. Reactivity of each phase with a series of aldehydes was examined. ¹³C CP/MAS NMR indicated that the tetraamine reacts stereoselectively with aldehydes to form cis-imine in the interlayer spacing. Depending on the molecular size of aldehyde, it is found that a significant difference can be recognized in the yields of the imine products for the two phases of intercalation compounds. It is also noted that residual water molecules in the interlayer spacing play an important role in the imine formation reaction.     

Magnetism of the (TMTSF)2X Family of Organic Conductors

Abstract

The magnetic properties of the (TMTSF)₂X series of conductors have been studied using magnetic susceptibility, electron spin resonance and both CW and pulsed NMR measurements. The results imply the existence of a spin-density-wave ground state, at ambient pressure, in at least the PF₆ ^?, AsF₆ ^? and SbF₆ ^? salts. The amplitude of the SDW, the exchange interaction, the anisotropy energy and the single particle gap are extracted from the experimental data.     

Low-Temperature Electron Spin Resonance in (TMTSF)2PF6 in the High Pressure Metallic Phase

Abstract

The electron spin resonance of (TMTSF)₂PF₆ has been observed at low fields (H_o < 110 Oe) in the high pressure, metallic phase (p > 6.5 kbar) in the temperature range 1-4^?K. The anisotropy in the g value is similar to that observed at ambient pressure above the metal-insulator transition. The linewidth is very narrow and the spin susceptibility strongly decreases as the superconducting transition is approached from above. We interpret this as evidence for singlet-paired superconductivity. Superconductivity is observed at 1.1 K and the critical field has angular dependence in the be plane. These observations lead us to conclude that (TMTSF)₂PF₆ is a singlet paired superconductor.     

Syntheses,Structural, and Biological Studies of Two New Peptide Compounds, 2(s)-(5-fluorouracil-1-aceto)amino-2-isopropyl Acetate Hemihydrate and 2(s)-(5-fluorouracil-1-aceto)amino-2-isopropyl Acetic Acid

Abstract  Two new peptide compounds, 2(s)-(5-fluorouracil-1-aceto)amino-2-isopropyl acetate hemihydrate (1:1/2H ₂ O) and 2(s)-(5-fluorouracil-1-aceto)amino-2-isopropyl acetic acid (2), have been synthesized and characterized by elemental analysis, IR, ¹H- and ¹³C NMR spectroscopy. Two new compounds were structurally characterized by single-crystal X-ray diffraction. The thermal stabilities of compounds 1:1/2H ₂ O and 2 were studied by DSC-TGA techniques. The result of the biological test showed that the compounds 1:1/2H ₂ O and 2 have certain antitumor activities. Index Abstract  Two new peptide compounds, 2(s)-(5-fluorouracil-1-aceto)amino-2-isopropyl acetate hemihydrate (1:1/2H2O) and 2(s)-(5-fluorouracil-1-aceto)amino-2-isopropyl acetic acid (2), have been synthesized and characterized by elemental analysis, IR, 1H-, and 13C NMR spectroscopy. Two new compounds were structurally characterized by single-crystal X-ray diffraction. The thermal stabilities of compounds 1:1/2H2O and 2 were studied by DSC-TGA techniques. The result of the biological test showed that the compounds 1:1/2H2O and 2 have certain antitumor activities.