Peculiarities of light propagation in chiral liquid crystal cells in an external electric field

We investigate the propagation of the extraordinary ray in a cell with a chiral liquid crystal at oblique incidence. For a 180° twist cell, we study the dependence of the minimum incidence angle at which the light does not yet pass through the cell on the applied voltage. The orientational structure of a liquid crystal in an external electric field has been calculated by directly minimizing the free energy. This has allowed the ray trajectories and the limiting refraction angles to be determined. The results of our calculations are consistent with the experiment. We show that allowance for the electric field nonuniformity in a chiral system is important for agreement between theory and experiment.     

Specific features of optical diffusion in nematic liquid crystals

Methods of computer simulation are used to study multiple light scattering in the ordered phase of a nematic liquid crystal. The development of the diffusion regime is studied in detail. It is demonstrated that the transient time depends on the external magnetic field and the direction of the incident radiation. The diffusion coefficients along and across the director are calculated. The validity of the diffusion approximation is controlled using the moments of the distribution function. Analysis of the diffusion coefficients versus the external field shows that the diffusion coefficients remain almost unchanged in the experimental range of the magnetic fields. In the presence of relatively strong fields, the diffusion coefficients increase due to a variation in the shape of the scattering indicatrix and the free-path length of photons. The dependence of the diffusion coefficients on the radiation wavelength is also calculated. Comparison of the simulated results and the experimental data shows that the calculated diffusion rate across the director virtually coincides with the experimental rate. The calculated diffusion coefficient along the director is substantially greater than the corresponding experimental rate.     

Photosensitizing Activity of Steroid Derivatives of Pyropheophorbide in the Oxidation of Tryptophan in the Aqueous Phase

Russian Journal of Physical Chemistry A - Solubilization with pluronic F-127 gave water-soluble forms of hydrophobic photosensitizers—steroid derivatives of pyropheophorbide a. Solubilization...     

Formation of a Cluster H<Subscript>2</Subscript>V<Subscript>10</Subscript>O<Stack><Subscript>28</Subscript><Superscript>4–</Superscript></Stack> under the Action of Brønsted Acids and Its Catalytic Activity in Oxidation of Alkylbenzenes

New method was developed for the preparation of vanadium cluster of the composition {Me₂NH₂}₄* H₂V₁₀O₂₈ from vanadyl(IV) acetylacetonate in the presence of 2-hydroxy-2-trifluoromethylchroman-4-one or its synthetic precursor, 2′-hydroxyacetophenone. The structure of the cluster was proved by X-ray diffraction (XRD) analysis. The cluster of decavanadate catalyzes oxidation of toluene and o-xylene creating promising situation for developing new catalytic materials.     

Effect of an electric field on the orientation of a liquid crystal in a cell with a nonuniform director distribution

The electric field-induced reorientation of a nematic liquid crystal in cells with a planar helicoidal or a homeoplanar structure of a director field is studied theoretically and experimentally. The dependences of the capacitances of these systems on the voltage in an applied electric field below and above the Fréedericksz threshold are experimentally obtained and numerically calculated. The calculations use the director distribution in volume that is obtained by direct minimization of free energy at various voltages. The inhomogeneity of the electric field inside a cell is taken into account. The calculation results are shown to agree with the experimental data.     

Synthesis of 1,3-diazapyrenes and 1,3,7-triazapyrenes by the reaction of 1,8-naphthalenediamine with triazine in the presence of carbonyl compounds or benzonitrile in polyphosphoric acid

A novel three-component synthesis has been developed for 1,3-diazapyrenes based on the reaction of 1,8-naphthalenediamine with triazine and carbonyl compounds in polyphosphoric acid (PPA). The use of benzonitrile in place of the carbonyl compounds in this reaction gives 6-phenyl-1,3,7-triazapyrenes. Dedicated to one of the best Russian chemists A. F. Pozharskii on his 70th jubilee. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 11, pp. 1694–1698, November, 2008.