Optical Properties of Planar Nanostructures Based on Semiconductor Quantum Dots and Plasmonic Metal Nanoparticles

The optical properties of a composite material consisting of a thin polymer film, which is activated by semiconductor CdSe/ZnS quantum dots (QDs) and silver nanoparticles, on a transparent dielectric substrate have been investigated. It is revealed that the presence of silver nanoparticles leads to an increase in the QD absorption (by a factor of 4) and in the fluorescence intensity (by a factor of 10), whereas the fluorescence time drops by a factor of about 10. Excitation of the composite medium by a pulsed laser is found to result in narrowing of the fluorescence band and a sublinear dependence of its intensity on the pulse energy. In the absence of silver nanoparticles, the fluorescence spectrum of QDs is independent of the excitation-pulse energy density, and the fluorescence intensity depends linearly on the pulse energy in the entire range of energy densities, up to 75 mJ/cm².     

Metal clusters and nanoparticles in dielectric matrices: Formation and optical properties

The optical properties of thin dielectric films with metal inclusions and their dependence on thermal and laser annealing are studied experimentally. Metal clusters (Ag, Au, and Cu) in dielectric materials (Al₂O₃ and SiO₂) are obtained by simultaneous vacuum deposition of metal and dielectric on the surface of a corresponding dielectric substrate (sapphire and quartz). It is shown that, depending on the deposited dielectric material, on the weight ratio of deposited metal and dielectric, and on the subsequent thermal treatment, one can obtain different metal structures, from clusters with a small number of atoms to complex dendritic plasmonic structures.     

Studying the regime of complete decoupling of the bond between the electron and nuclear moments at the <Emphasis Type="Italic">D</Emphasis><Subscript>1</Subscript>-line of the <Superscript>39</Superscript>K potassium isotope using a spectroscopic microcell

Atomic transitions of the ³⁹K potassium isotope in strong (up to 1 kG) longitudinal and transverse magnetic fields have been studied with a high spectral resolution. It has been shown that crossover resonances are almost absent in the saturated absorption spectrum of potassium vapors in a 30-μm-thick microcell. This, together with the small spectral width of atomic transitions (~30 MHz), allows one to use the saturated absorption spectrum for determining frequencies and probabilities of individual transitions. Among the alkali metals, potassium atoms have the smallest magnitude of the hyperfine splitting of the lower level. This allows one to observe the break of the coupling between the electronic and nuclear angular momentums at comparatively low magnetic fields B > 500 G, i.e., to implement the hyperfine Paschen–Back regime (HPB). In the HPB regime, four equidistantly positioned transitions with the same amplitude are detected in circularly polarized light (σ⁺). In linearly polarized light (π) at the transverse orientation of the magnetic field, the spectrum consists of eight lines which are grouped in two groups each of which consists of four lines. Each group has a special distinguished G-transition and the transition that is forbidden in the zero magnetic field. In the HPB regime, the probabilities of transitions in a group and derivatives of their frequency shifts with respect to the magnetic field asymptotically tend to magnitudes that are typical for the aforesaid distinguished G-transition. Some practical applications for the used microcell are mentioned.     

Catalytic hydroformamination of 2,5-dimethoxy-2,5-dihydrofurans

N-Substituted 3- and 4-formylpyrroles have been obtained by hydroformamination of 2,5-dimethoxy-2,5-dihydrofurans in the presence of HRh(CO)(PPh₃)₃.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 8, pp. 1837–1840, August, 1990.     

Synthesis of New 1,4-Benzodioxanуl-1,2,4-triazole Derivatives

The reaction of 5-(1,4-benzodioxan-2-yl)-4H-1,2,4-triazole-3-thiol with N-substituted chloroacetic acid amides obtained by condensation of chloroacetyl chloride with various primary amines furnished a series of S-amidomethyl derivatives. The corresponding thiazolotriazolone prepared from 2-[5-(1,4-benzodioxan-2-yl)-4H-1,2,4-triazol-3-ylthio]acetic acid reacted with aromatic aldehydes to form arylidene derivatives.

     

Interaction of ethoxyacetaldehyde with 1,3-dicarbonyl compounds

It has been established that on interaction of ethoxyacetaldehyde with acetyl-acetone, acetoacetic ester, and benzoylacetone in the presence of piperidine acetate, ,-unsaturated compounds are formed, viz., 3-(2-ethoxy)vinyl substituted acetylacetone, acetoacetic ester, and benzoylacetone. Methods are proposed for the synthesis of 2,3,5-trisubstituted 4,5-dihydrofurans in the presence of trifluoroacetic or acetic acids by the cylization of the linear condensation products.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 3, pp. 308–311, March, 1986.     

Reactions of 1,1-diacetylcyclopropane over a palladium catalyst

Conclusions 1,1-Diacetylcyclopropane, in the vapor phase over 5% Pd/C modified by DMSO, undergoes conversion to 2-methyl-3-acetylfuran and 3-ethylpentane-2,4-dione.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 7, pp. 1663–1664, July, 1984.     

Synthesis of 2,4-dimethyl-3-acetyl-l,6-dioxaspiro[4,4]non-2-ene

Conclusions A synthesis is reported for 2,4-dimethyl-3-acetyl-1,6-dioxaspiro[4,4]nan-2-ene, which is the first example of a trisubstituted spiroketal.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 1, pp. 209–210, January, 1985.     

Interconversions of heterocycles containing S,N, and O

On heating with hydrogen sulfide in the presence of sulfuric acid, tetrahydropyran-4-ones (III) and 4-piperidones (II) are converted to the corresponding thiopyranones (I). The anticipated III are obtained by heating I or II in dilute sulfuric acid solution in the presence of mercuric sulfate. Analogously, I and II in aqueous methylamine solution are converted to II;2,3,6-trimethyl-4-pyrone (VII) and 1, 2, 3, 6-tetramethyl-4-pyridonen (VIII) are also interconvertible.