Pyrolytic synthesis and Eu→Eu reduction process of blue-emitting perovskite-type BaLiF3:Eu thin films

Perovskite-type barium lithium fluoride (BaLiF₃) was synthesized by pyrolysis of metal trifluoroacetates. The reaction temperature necessary for producing a single-phase material was found to be 600°C, which was lower than that for a conventional solid-state reaction or a melting method. Eu-doped BaLiF₃ was also prepared and characterized to examine the suitability of trifluoroacetates for precursors in synthesizing homogeneous complex metal fluoride materials. It was demonstrated that trivalent Eu³⁺, which was used as acetate for a starting material, was reduced to divalent Eu²⁺ in the pyrolysis process of BaLiF₃, as indicated by a broad blue emission due to an allowed 4f⁶5d→4f⁷ transition at 408 nm with a ultraviolet excitation at 254 nm. The concentration quenching of the blue emission occurred at 5 at% of Eu in BaLiF₃, indicating that Eu was homogeneously dispersed in the BaLiF₃ host lattice. Mechanisms of the formation and reduction process of BaLiF₃ were discussed based on pertinent chemical reactions.     

Structure of Aqueous Gallium(III) Bromide Solutions Over a Temperature Range 80–333 K by Raman Spectroscopy, X-ray Absorption Fine Structure, and X-ray Diffraction

The structure and complex formation of concentrated aqueous gallium(III) bromide (GaBr₃) solutions have been investigated over a temperature range 80–333 K by Raman spectroscopy, X-ray absorption fine structure (XAFS), and X-ray diffraction. The Raman spectra obtained at various [Br^?]/[Ga³⁺] molar ratios and temperatures have shown that complex formation between Ga³⁺ and Br^? occurs as a predominant species, with [GaBr₄]^? at [Ga³⁺] as high as 1～2 M (M = mol?dm ^?3) and [Br^?]/[Ga³⁺] ratios > ～2, and that cooling of the solutions favors the formation of the aqua Ga³⁺. The intermediate species were not seen in the Raman spectra. The XAFS data have revealed that the aqua complex has a sixfold coordination as [Ga(H₂O)₆]³⁺ with a Ga³⁺–H₂O distance of (1.96 ± 0.02) Å, whereas the [GaBr₄]^? complex has a Ga³⁺–Br^? distance of (2.33± 0.02) Å, and that vitrification of the aqueous GaBr₃ solution at liquid nitrogen temperature shifts the equilibrium toward the aqua complex. The X-ray diffraction data at different subzero temperatures have shown a tendency of decreasing Ga³⁺–Br^? and increasing Ga³⁺–H₂O interactions with lowering temperature, confirming the preference of aqua Ga³⁺ in the supercooled liquid state as well as in the glassy state. The Ga³⁺–H₂O distance of ～1.8 Å for the tetrahedral coordination was found in a 2.01 M gallium(III) bromide solution with a [Br^?]/[Ga³⁺] ratio of 3.7 and gradually increased to a value of 1.92 Å for octahedral geometry with decreasing temperature, suggesting that equilibrium shifts from [GaBr₄]^? to [Ga(H₂O)₆]³⁺ through intermediate species, [GaBr _n ]^(3?n)+ (n = 2 and 3). The Ga³⁺–Br^? and Br^?–Br^? distances within [GaBr₄]^? with an almost tetrahedral symmetry are (2.35± 0.02) and (3.82± 0.03) Å, respectively. The Ga³⁺ has the second hydration shell at (4.03± 0.03) Å and the hydration of Br^? is characterized with a Br^?–H₂O distance of (3.35± 0.02) Å at all temperatures investigated.     

Dielectric relaxation in the paracrystalline phase in polyacrylonitrile

Thermal expansion and dielectric relaxation of polyacrylonitrile were measured in the temperature range from ?75 to 152°C. at frequencies from 30 cps to 3 Mc./sec. The thermal expansion curve and the temperature dependence of logarithmic relaxation time both show an inflection at 85°C. An x-ray study by Bohn reveals that this inflection comes from the thermal expansion of the paracrystalline phase of this polymer, and consequently the transition at 85°C. and the associated relaxation are ascribed to molecular motion in the paracrystalline phase. The relaxation strength increases with increasing temperature above this point. The transition is caused by freezing of the bending vibration of chains whereas the relaxation results from rotational vibration. The length of segments in this phase is roughly estimated to be ca. 100 A. by comparing the observed relaxation strength with the theory developed on the basis of the above considerations.     

One-pot preparation of chiral beta-amino esters by rhodium-catalyzed three-components coupling reaction

Chiral beta-amino esters are synthesized in one-pot from three components, amines, aldehydes, and ethyl bromoacetate, under the rhodium-catalyzed Reformatsky-type reaction condition, where complete diastereoselection is achieved in the nucleophilic addition step of ethyl bromoacetate to the imines prepared in     

Synthesis of 4,6-disubstituted 2-methylpyridines and their 3-carboxamides

A new one-pot synthesis of title compounds by the reactions of α,β-unsaturated carbonyl compounds with β-aminocrotononitrile in the presence of sodium hydroxide is described.     

Total Synthesis of Indole and Dihydroindole Alkaloids. XVIII. Isomers and analogues of vinblastine

The synthesis and conformational analysis of (3′R)-3-hydroxyleurosidine ( 5 ), (3′S)-3-hydroxyleurosidine ( 10 ), (3′S)-3-acetoxy-4′-deoxyleurosidine ( 15 ), (3′R)-3-acetoxy-4′-deoxyleurosidine ( 23 ), (3′R)-3-acetoxy-4′-deoxyvinblastine ( 16 ), (3′S)-3-acetoxy-4′-deoxyleurosidine ( 28 ) is discussed.     

First synthesis of 1,9-dideoxyforskolin from ptychantin A

1,9-Dideoxyforskolin 2 has been synthesized starting from ptychantin A 3.     

RECENT PROGRESS OF NANO-MECHANICAL MAPPING

 Nano-mechanical mapping by atomic force microscopy has been developed as an useful application to measure mechanical properties of soft materials at nanometer scale. To date, the Hertzian theory was used for analyzing force-distance curves as the simplest model among several contact mechanics between elastic bodies. However, the preexisting methods based on this theory do not consider the adhesive interaction in principle, which cannot be neglected in the ambient condition. A new analytical method was introduced to estimate the elasticity and the adhesive energy simultaneously by means of the JKR theory, describing adhesive contact between elastic materials. Poly(dimethylsiloxane) (PDMS) and isobutylene-co-isoprene rubber (IIR) were analyzed to verify the applicable limit of the JKR analysis. For elastic samples such as PDMS, the force-deformation plots obtained experimentally were consistent with JKR theoretical curves. Meanwhile, for viscoelastic samples, especially for IIR, the experimental plots revealed large deviations from JKR curves depending on scanning velocity and maximum loading force. Some nano-rheological arguments were employed based on the difference between these specimens.