Colorimetric and fluorometric sensing of the Lewis acidity of a metal ion by metal-ion complexation of imidazo[1,2-a]pyrazin-3(7H)-ones

Metal-ion complexation of 7-benzylimidazo[1,2-a]pyrazin-3(7H)-one derivative (2) with Li⁺, Mg²⁺, Ca²⁺, Ba²⁺, Sc³⁺, and La³⁺ in acetonitrile resulted in successive modulations of its UV/vis absorption and fluorescence spectroscopic properties. This result indicates that 2 can be used as a colorimetric and fluorometric sensor of the Lewis acidity of a metal ion in aprotic solutions. The hypothesis that the metal-ion complex has a O10(imidazopyrazinone)-metal ion bond was supported by X-ray crystallographic analysis and quantum chemical calculations for a Li⁺ complex of 7-methylimidazo[1,2-a]pyrazin-3(7H)-one derivative (1).     

Dynamic Vapochromic Behaviors of Organic Crystals Based on the Open–Close Motions of S‐Shaped Donor–Acceptor Folding Units

The first vapochromic organic crystals are described with respect to their preparation, color change, adsorption/desorption properties, crystal structures, and color‐change mechanism. Non‐solvatochromic, 1,4,5,8‐naphthalene‐tetracarboxylic diimide (NDI) derivatives 1 a bearing two pyrrole imine (PI) tethers have been used as a motif for the crystal packing template. Red‐purple vapochromic solid 3 was prepared by evacuation of orange crystals 2 (equivalent to 1 a ?2 MeOH), obtained by recrystallization of 1 a from MeOH. Solid 3 showed high‐adsorption ability and unprecedented vapor‐dependent color changes upon exposure to a variety of organic vapors, whereas light brown amorphous solid 1 a , did not show vapo‐ or solvatochromic behavior toward any organic solvent. The strong adsorption capability of 3 was confirmed by TGA experiments and adsorption/desorption isotherms. Analysis of the solid‐state UV/Vis analysis revealed that the vapor‐dependent color changes of 3 were owed to the specific interference of solvent vapors with its broad CT absorbance at λ=450–650 nm. Packing structures of 1 a in orange crystals 2 , red‐purple solid 3 , and regenerated orange solid 2 were unequivocally established by single crystal and synchrotron powder X‐ray diffraction, respectively. Molecular structures and arrays of 1 a in these materials indicated that 1) unit 1 a had an S‐shaped folded conformation in 2 and 3 by intramolecular donor–acceptor interactions between NDI and two PI units; 2) inclusion of the guest vapor into the S‐shaped template decreased the intramolecular PI‐NDI interactions, accompanied by increasing intermolecular NDI‐NDI and PI‐PI interactions; and 3) such flexible, open–close motions of the S‐shaped template could be repeated during reversible adsorption/desorption processes without degradation of crystal packing. The adsorption properties and mechanism of molecular shape‐dependent vapochromic behavior of 3 are discussed with reference to experimental results, crystallographic data, and theoretical calculations.     

Effects of hyperons in binary neutron star mergers

Numerical simulations for the merger of binary neutron stars are performed in full general relativity incorporating both nucleonic and hyperonic finite-temperature equations of state (EOS) and neutrino cooling. It is found that even for the hyperonic EOS, a hypermassive neutron star is first formed after the merger for the typical total mass ≈2.7M(⊙), and subsequently collapses to a black hole (BH). It is shown that hyperons play a substantial role in the postmerger dynamics, torus formation around the BH, and emission of gravitational waves (GWs). In particular, the existence of hyperons is imprinted in GWs. Therefore, GW observations will provide a potential opportunity to explore the composition of neutron star matter.     

Evolution of the Kondo effect in a quantum dot probed by shot noise

We measure the current and shot noise in a quantum dot in the Kondo regime to address the nonequilibrium properties of the Kondo effect. By systematically tuning the temperature and gate voltages to define the level positions in the quantum dot, we observe an enhancement of the shot noise as temperature decreases below the Kondo temperature, which indicates that the two-particle scattering process grows as the Kondo state evolves. Below the Kondo temperature, the Fano factor defined at finite temperature is found to exceed the expected value of unity from the noninteracting model, reaching 1.8±0.2.     

Fabrication of a freestanding GaN layer by direct growth on a ZnO template using hydride vapor phase epitaxy

A new hydride vapor phase epitaxy (HVPE)-based approach for the fabrication of freestanding GaN (FS-GaN) substrates was investigated. For the direct formation of low-temperature GaN (LT-GaN) layers, the growth parameters were optimized: the polarity of ZnO, the growth temperature, and the V/III ratio. The FS-GaN layer was achieved by gas etching in an HVPE reactor. A fingerprint of Zn out-diffusion was detected in the photoluminescence measurements, especially for the thin (80 μm) FS-GaN film; however, a thicker film (400 μm) was effectively reduced by optimization of GaN growth.     

Aerobic reduction of olefins by in situ generation of diimide with synthetic flavin catalysts

A versatile reducing agent, diimide, can be generated efficiently by the aerobic oxidation of hydrazine with neutral and cationic synthetic flavin catalysts 1 and 2. This technique provides a convenient and safe method for the aerobic reduction of olefins, which proceeds with 1 equiv of hydrazine under an atmosphere of O(2) or air. The synthetic advantage over the conventional gas-based method has been illustrated through high hydrazine efficiency, easy and safe handling, and characteristic chemoselectivity. Vitamin B(2) derivative 6 acts as a highly practical, robust catalyst for this purpose because of its high availability and recyclability. Association complexes of 1b with dendritic 2,5-bis(acylamino)pyridine 15 exhibit unprecedented catalytic activities, with the reduction of aromatic and hydroxy olefins proceeding significantly faster when a higher-generation dendrimer is used as a host pair for the association catalysts. Contrasting retardation is observed upon similar treatment of non-aromatic or non-hydroxy olefins with the dendrimer catalysts. Control experiments and kinetic studies revealed that these catalytic reactions include two independent, anaerobic and aerobic, processes for the generation of diimide from hydrazine. Positive and negative dendrimer effects on the catalytic reactions have been ascribed to the specific inclusion of hydrazine and olefinic substrates into the enzyme-like reaction cavities of the association complex catalysts.