Wide-line <Superscript>1</Superscript>H NMR study of mesomorphic states of 4′-(octyloxy)-4-biphenylcarbonitrile

A sample of 4′-(octyloxy)-4-cyanobiphenyl (8OCB) was studied in the temperature range −60–80°C by wide-line ¹H NMR. The line shapes, half-widths, and second moments were determined. For the smectic phase of 8OCB, the relaxation times T ₁ and T ₂, the correlation time τ_c, and the degree of order were estimated. The ¹H NMR spectral patterns and characteristics were found to be quite different for the crystalline, smectic, and nematic phases of 8OCB, which makes it possible to reliably identify the corresponding transitions and assess the molecular dynamics and molecular order of a structure. The temperature ranges, stability conditions, and other characteristics of the liquid crystalline phases that form on heating 8OCB were determined.     

Synthesis,physicochemical and coordination properties of 5,15-diphenyltetramethyltetraethylporphyn nitro derivatives

The 5,15-diphenyl-3,7,13,17-tetramethyl-2,8,12,18-tetraethylporphyrin nitro derivatives containing the nitro groups in the meso-positions of the porphyn ring and/or para-positions of phenyl rings were synthesized. Porphyrins were characterized by electron absorption, ¹H NMR, and IR spectra. The purity and individuality of the synthesized compounds was proved by TLC and elemental analysis. Kinetic parameters of complexation reactions of the synthesized porphyrins with copper acetate in pyridine and in the mixed solvent benzene-acetic acid (7:3) depend on the degree of deformation of the tetrapyrrole cycle, on the solvation effects and electronic effects of the nitro groups.     

X-ray diffraction study of p-(alkoxybenzylidene)-p′-toluidines: Crystal and molecular structure of C10H21O-C6H4-CH=N-C6H4-CH3

The crystal and molecular structure of p-(decaoxybenzylidene)-p′-toluidine C₁₀H₂₁O-C₆H₄-CH=N-C₆H₄-CH₃ is studied. The molecule is nearly planar. In the crystal packing, loose regions formed by aliphatic fragments of molecules alternate with pseudostacks of aromatic fragments of molecules that are related by the centers of symmetry. The stacks are built of dimers, in which molecules are linked by π-stacking interactions between benzene rings. There are no weak directional interactions between dimers in a stack. The presence of a single structure-forming element in the crystal, namely, the π-stacking interactions in the dimers, along with the similarity of the crystal packing to that of the C₈H₁₇O-homologue, which forms a nematic mesophase on melting, indicate that the crystals under study should exhibit nematic properties.     

Energy band structure and Frenkel excitons in PbGa2S4

Optical reflection spectra are measured and calculated in PbGa₂S₄ crystals in the region of resonances related to excitons with large oscillator strength and binding energy (Frenkel excitons). The splitting of the upper valence band in the center of the Brillouin zone due to crystal field (Δ_cf) and spin orbit (Δ_so) interaction are determined. Optical reflection spectra are measured and calculated according to Kramers-Kronig relations in the region of 3-6 eV in Е⊥с and Е∥с polarizations, and the optical constants n, k, ε₁ and ε₂ are determined. The observed electronic transitions in PbGa₂S₄ crystals are discussed in the frame of theoretical energy band structure calculation for thiogallate crystals.     

Energy band structure and optical constants of ZnAs2 crystals

The fine structure of the Fabry–Perot interference as well as the interference of ordinary and extraordinary waves is investigated in ZnAs₂ crystals. ε_1, ε_2, n and k optical constants are calculated in a wide spectral range of 0.4–12 eV. The anisotropy of electronic transitions at the minimum energetic interval of the band structure is investigated. The interband energetic intervals are determined deep into the absorption band. The observed transitions are discussed taking into account the available data from the band structure calculations.     

Molecular and crystal structure of 4-alkoxybenzoic acids: Design of the mesogenic phase

The crystal and molecular structures of 4-alkoxybenzoic acids C _n H_{2n + 1}-O-C₆H₄-COOH, n = 4–12, which are nematic (n = 4–6) or smectic-nematic (n = 7–12) mesogenes, are studied. No direct relationship between the molecular geometry and mesogenic properties is found. All the crystal structures contain dimers formed by pairs of O…H-O hydrogen bonds between carboxyl groups. Crystals belonging to the group of smectic-nematic liquid crystals (SNLC) are built of separate regions, namely, loosely packed aliphatic regions and closely packed aromatic regions with significant π-stacking interactions. Loose aliphatic regions occur in crystals belonging to the group of nematic liquid crystals (NLC); however, they are surrounded by dense aromatic regions and do not run throughout the crystal. In NLC, π-stacking interactions are far weaker than in SNLC. At the early stage of melting of SNLC crystals, structurized associates due to both π-stacking interactions and hydrogen bonds are retained in the melt (smectic phase), whereas, upon further heating, only hydrogen-bonded associates are left (nematic phase). In the course of melting of NLC, only hydrogen-bonded dimers are retained in the melt (nematic phase).     

Synthesis of tetraphenylporphins with active groups in the phenyl rings. 2. Preparation of tetrakis(hydroxyphenyl)porphins

The corresponding tetrakis(hydroxyphenyl)porphins were obtained by demethylation of tetrakis(methoxyphenyl)porphins with aniline hydrochloride or 60% HBr.See [1] for communication 1.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 10, pp. 1359–1361, October, 1983.     

Dielectric Properties of 4-(2,3-Epoxypropoxy)- and 4-Propoxy-4'-alkoxyazoxybenzenes

The temperature dependences of the dielectric permittivity of 4-(2,3-epoxypropoxy)-4'-alkoxyazoxybenzenes (n = 1-10) and 4-propoxy-4'-alkoxyazoxybenzenes (n = 1-10) with mesomorphic properties were measured by dielectrometry. The introductrion of the terminal epoxy group increases the dielectric permittivity and its anisotropy. The dipole moments of molecules of 4-(2,3-epoxypropoxy)-4'-alkoxyazoxybenzenes (n = 1-10) and 4-propoxy-4'-alkoxyazoxybenzenes (n = 1-10) were determined by the second Debye method. The epoxy-substituted azoxybenzenes have higher dipole moments than their structural analogs.     

p-V m-x Properties of Water-Dimethylformamide System at 288.15 K over the Pressure Range 0.1-100 MPa

The compressibility factors k ((p ₀) - ta;(p))/ta;(p ₀ )) of water-dimethylformamide (DMF) binary mixtures are measured over the entire concentration range at 288.15 K and pressures of up to 100 MPa with a constant-volume piezometer. The specific and molar volumes in the water-DMF system are estimated as well as the isothermal compressibility coefficient s and excess and partial molar volumes of the system components. The composition dependence of the specific volume in the water-DMF system has extrema, its shape being pressure-dependent; such a dependence of the compressibility factor passes through a minimum; and the partial coefficient of the isothermal compressibility of water has an inversion point.     

Exciton–phonon luminescence and Raman scattering in CuGaS2 crystals

Photoluminescence and resonance Raman scattering spectra of CuGaS₂ crystals are investigated at low temperature (10 K) under the excitation with the radiation from a spectral interval obtained by passing the radiation of an incandescent or xenon lamp through a monochromator. The thermalized luminescence of the Γ₄ and Γ₅ excitons was revealed under the excitation by an interval of photon energies higher than the energy of the ground state of long-wavelength Γ₄ excitons (ω_Т(Γ₄) + ). The energy conversion between the polariton modes in luminescence and resonance Raman scattering spectra is considered.