Fluorescence Study of Excited-State Relaxation Processes of 2-Pyridyl-5-Aryloxazoles

Anomalously high fluorescence spectrum Stokes' shifts of 2(4-pyridyl)-5-(4-methylphenyl)oxazole, 2(4-pyridyl)-5-(4-methoxyphenyl)oxazole, 2(4-pyridyl)-5-(4-N,N-dimethylaminophenyl)oxazole have been found. The fluorescence spectra of the compounds studied are shifted to longer wavelengths as the solvent dielectric constant increases. The dipole moments of these compounds increase by 3–4 times upon excitation. The fluorescence spectra of the compounds investigated are shifted to shorter wavelengths, and the fluorescence quantum yields increase as the temperature decreases. The fluorescence rate constant of 2(4-pyridyl)-5-(4-N,N-dimethylaminophenyl)oxazole changes slightly as the temperature decreases from 293 K (relaxed state) to 114 K (mainly nonrelaxed state). It was concluded that the anomalously high fluorescence Stokes' shift of 2-pyridyl-5-aryloxazole derivatives is caused by solvent orientation relaxation.     

Synthesis and optical properties of nanohybrids in the system constituted by silica and lanthanide phosphoramide complexes

Sol-gel process of hydrolytic polycondensation of tetramethoxysilane with trimethoxysilyl derivatives of lanthanide phosphoramide complexes was studied in order to obtain photoluminescent organic-inorganic hybrid materials. Original Russian Text N.N. Khimich, Yu.L. Zub, L.A. Koptelova, T.S. Mashchenko, E.P. Troshina, M.G. Voronkov, 2006, published in Zhurnal Prikladnoi Khimii, 2006, Vol. 79, No. 11, pp. 1789–1794.     

Photolysis of 5-diazo-2,2-dimethyl-4,6-dioxo-1,3-dioxane (diazoisopropylidenemalonic acid)

The principal pathway in the photochemical ( > 210 nm) transformation of 5-diazo-2,2-dimethyl-4,6-dioxo-1,3-dioxane in an aqueous medium (or in methanol) is splitting out of nitrogen and the Wolff rearrangement to give the stable 2,2-dimethyl-5-oxo-1,3-dioxolane-4-carboxylic acid (or its methyl ester), which undergoes decarboxylation only at temperatures above 150 ° C, whereas it undergoes hydrolysis to a hydroxymalonic acid in the presence of trifluoroacetic acid.Communication 6 from the series Chemistry of diazo dicarbonyl compounds. See [1] for Communication 5.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 3, pp. 321–325, March, 1985.     

Sol-gel synthesis of dispersed ZrO2 nanoparticles

The influence exerted by the basicity of organic amines on hydrolytic polycondensation of zirconium tetraisopropoxide was studied in order to obtain nanodispersed ZrO₂ particles of various sizes.     

Composition-induced transition of spin-modulated structure into a uniform antiferromagnetic state in a Bi<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>La<Subscript>x</Subscript>FeO<Subscript>3</Subscript> system studied using <Superscript>57</Superscript>Fe NMR

By analyzing the NMR line shape, the transformation of a spatially spin-modulated magnetic structure in BiFeO₃ into an ordinary spatially uniform structure of the LaFeO₃ orthoferrite in Bi_1?xLa_xFeO₃ solid solutions is studied. The measurements are made using a spin-echo technique at temperatures of 77 and 4.2 K on ceramics with compositions x=0, 0.1, 0.2, 0.61, 0.9, and 1.0 enriched by the ⁵⁷Fe isotope. It is shown that the spin-modulated structure disappears near the concentration x=0.2, which corresponds, according to the published data, to the phase transition with a change in the unit-cell symmetry R3c → C222. A formula is obtained describing the NMR absorption line shape for the spin-modulated structure with account of local line-width. Theoretical spectra adequately describe the evolution of the experimental spectrum in the concentration range 0≤x≤0.2. Highly nonuniform local magnetic fields in the intermediate compositions make it impossible to detect NMR signals in a sample with x=0.61. A uniform magnetic structure characterized by a single narrow line arises in the range of existence of a phase with the symmetry Pnma typical of the pure orthoferrite LaFeO₃.     

Peculiarities of temperature and orientation dependences of Al-Be-Mg alloy work hardening curves in temperature range 30–300 K

The mechanical properties of high modulus alloy ABM-I are studied between 30 and 300 K. The behaviour of work hardening curves is found to be affected appreciably by both temperature and sample orientation with respect to the ingot axis. The fracture surface type is found to correlate with material strength parameters.We would like to express our thanks to V. V. Sergienko for carrying out the structural studies.     

THERMODYNAMIC AND PARTICLE-DYNAMIC STUDIES ON SYNTHESIS OF SILICA NANOPARTICLES USING MICROWAVE-INDUCED PLASMA CVD

1. Introduction1.1 Silica nanoparticles and synthesis methods Silica (SiO2) nanoparticles are widely used in industry asan active filler for polymer reinforcement, a rheologicaladditive in fluids, a free flow agent in powders, and anagent for chemical mechanical polishing during IC (inte-grated circuit) fabrication (Sniegowski & de Boer, 2000).Silica powder is also used for producing silicon carbide(Koc & Cattamanchi, 1998) or opaque silica aerosols (Leeet al., 1995). Many methods can …     

Solvothermal synthesis of photocatalytically active titania in acetic acid

A new solvothermal method has been developed for preparing nanocrystalline titania powders by reacting titanium isopropoxide with acetic acid. The photocatalytic activity of a sample prepared at 250°C is shown to far exceed the activity of a commercially available sample.     

Use of an Acrylic Dendron-containing Monomer in the Synthesis of a Macroporous Polymeric Material

A procedure was developed for preparing a monolithic macroporous material by photoinitiated co-polymerization of glycidyl methacrylate, ethylene glycol dimethacrylate, and an acrylic comonomer containing a dendron with protected terminal amino groups. The macropore formation is provided by a blowing agent.__________Translated from Zhurnal Prikladnoi Khimii, Vol. 78, No. 4, 2005, pp. 629-633.Original Russian Text Copyright © 2005 by Khimich, Tennikova.