Novel formation of diimidazo[1,2-a:2',1'-c]quinoxaline derivatives and their optical properties

Reaction of 1,2-di(imidazolyl)benzene treated with n-BuLi proceeded to give diimidazo[1,2-a:2',1'-c]quinoxaline in the presence of iodine or Pd(PPh(3))(4). Blue fluorescence was observed from 3,10-diarylated diimidazoquinoxalines with high quantum yield. They were also applied to organic light-emitting devices as emitters, in which the diphenyl derivative emits a nearly pure blue light.     

X-ray imaging of newly-developed gadolinium compound/silica core–shell particles

A preparation method for gadolinium compound (Gd) nanoparticles coated with silica (Gd/SiO₂) is proposed. Gd nanoparticles were prepared with a homogeneous precipitation method at 80 °C using 1.0 × 10⁻³ M Gd(NO₃)₃ and 0.5 M urea in the presence of 1.0 g/L stabilizer. Among stabilizers examined. Sodium n-dodecyl sulfate (SDS) was suitable as the stabilizer for preparing small Gd nanoparticles, and consequently Gd nanoparticles with a size of 46.2 ± 12.4 nm were prepared using the SDS. Silica-coating of the Gd nanoparticles was performed by a St?ber method at room temperature using 0.013 M TEOS and 2.0 × 10⁻³ M NaOH in water/1-propanol solution in the presence of 1.0 × 10⁻³ M Gd nanoparticles, which resulted in production of Gd/SiO₂ particles with an average size of 64.2 ± 14.4 nm. The Gd/SiO₂ particles were surface-modified with 3-aminopropyltrimethoxysilane and succinic anhydride. It was confirmed by measurement of electrophretic light scattering that amino group or carboxyl group was introduced onto the Gd/SiO₂ particles. The gadolinium concentration of 1.0 × 10⁻³ M in the as-prepared colloid solution was increased up to a gadolinium concentration of 0.4 M by centrifugation. The core–shell structure of Gd/SiO₂ particles was undamaged, and the colloid solution was still colloidally stable, even after the concentrating process. The concentrated Gd/SiO₂ colloid solution showed an X-ray image with contrast as high as a commercial Gd complex contrast agent. Internal organs in a mouse could be imaged injecting the concentrated colloid solution into it.     

Structural design of easy-axis magnetic anisotropy and determination of anisotropic parameters of Ln(III)-Cu(II) single-molecule magnets

Four dinuclear Ln^III? Cu^II complexes with Ln=Tb ( 1 ), Dy ( 2 ), Ho ( 3 ), and Er ( 4 ) were synthesized to investigate the relationship between their respective magnetic anisotropies and ligand‐field geometries. These complexes were crystallographically isostructural, and a uni‐axial ligand field was achieved by using three phenoxo oxygen groups. Complexes 1 and 2 displayed typical single‐molecule magnet (SMM) behaviors, of which the out‐of‐phase susceptibilities were observed in the temperature range of 1.8–5.0 K ( 1 ) and 1.8–20.0 K ( 2 ). The Cole–Cole plots exhibited a semicircular shape with α parameters in the range of 0.08–0.18 (2.6–4.0 K) and 0.07–0.24 (3.5–7.0 K). The energy barriers Δ/k_B were estimated from the Arrhenius plots to be 32.9(4) K for 1 and 26.0(5) K for 2 . Complex 3 displayed a slow magnetic relaxation below 3.0 K, whereas complex 4 did not show any frequency‐dependent behavior for both in‐phase and out‐of‐phase susceptibilities, which indicates that easy‐axis anisotropy was absent. The temperature dependence of the dc susceptibilities for the field‐aligned samples of 1 – 3 revealed that the χ_MT value continuously increased as the temperature was lowered, which indicates the presence of low‐lying Stark sublevels with the highest |J_z| values. In contrast, complex 4 displayed a smaller and temperature‐independent χ_MT value, which also indicates that easy‐axis anisotropy was absent. Simultaneous analyses were carried out for 1 – 3 to determine the magnetic anisotropy parameters on the basis of the Hamiltonian that considers B₂⁰, B₄⁰, and B₆⁰.     

Magnetic anisotropies in paramagnetic polynuclear metal complexes

The study of the magnetic properties of highly anisotropic paramagnetic molecules is an area of intense current research interest. Of these, single-molecule magnets (SMMs) and single-chain magnets (SCMs) showing non-equilibrium magnetization have remained a key topic over the past two decades. The slow magnetization reversals found in SMMs and SCMs are contingent on two requirements: a large ground-state spin forbidding direct quantum transitions of spin reversal, and a series of excited spin levels, due to the anisotropy of the system, which can act as steppingstones for the thermal relaxation of the spin orientations (the Orbach process). In this critical review, the latter requirement, i.e. the existence of magnetic anisotropies in paramagnetic species, is reviewed with the aim of providing clues towards the rational design of molecule-based magnets (100 references).     

Two types of two-component gels formed from pseudoenantiomeric ethynylhelicene oligomers

Two-component gels formed from pseudoenantiomeric ethynylhelicene oligomers in toluene exhibited two different properties depending on difference in numbers of helicenes in the two components. The combinations (M)-5/(P)-4, (M)-6/(P)-4, and (M)-7/(P)-4, which contained oligomers with comparable numbers of helicenes, formed transparent gels (Type I gels). The combinations (M)-6/(P)-3, (M)-7/(P)-3, and (M)-8/(P)-3, which contained oligomers with considerably different numbers of helicenes, formed turbid gels (Type II gels). Negative Cotton effects were observed for the Type I gels in the region between 350 and 450 nm, and were positive for the Type II gels, despite the use of (M)-oligomers for the longer components. UV/vis exhibited absorption maxima at 350 nm for the Type I gels and at 338 nm for the Type II gels. Different behaviors in gel formation processes were observed by fluorescence studies. Atomic force microscopy analysis showed fiber structures of 25-50 nm diameter for Type I gels and bundles of 100-150 nm diameter for Type II gels. The stoichiometry in gel formation also differed: The Type I gels showed 1:1 stoichiometry of the two components; the Type II gels showed no 1:1 stoichiometry, likely 1:2 stoichiometry. Using the Type I and II gels, two-layer gel systems were constructed.     

Vibrational dynamics of acetate in D2O studied by infrared pump-probe spectroscopy

Solute-solvent interactions between acetate and D(2)O were investigated by vibrational spectroscopic methods. The vibrational dynamics of the COO asymmetric stretching mode in D(2)O was observed by time-resolved infrared (IR) pump-probe spectroscopy. The pump-probe signal contained both decay and oscillatory components. The time dependence of the decay component could be explained by a double exponential function with time constants of 200 fs and 2.6 ps, which are the same for both the COO asymmetric and symmetric stretching modes. The Fourier spectrum of the oscillatory component contained a band around 80 cm(-1), which suggests that the COO asymmetric stretching mode couples to a low-frequency vibrational mode with a wavenumber of 80 cm(-1). Based on quantum chemistry calculations, we propose that a bridged complex comprising an acetate ion and one D(2)O molecule, in which the two oxygen atoms in the acetate anion form hydrogen bonds with the two deuterium atoms in D(2)O, is the most stable structure. The 80 cm(-1) low-frequency mode was assigned to the asymmetric stretching vibration of the hydrogen bond in the bridged complex.     

A switchable molecular rotator: neutron spectroscopy study on a polymeric spin-crossover compound

A quasielastic neutron scattering and solid-state (2)H NMR spectroscopy study of the polymeric spin-crossover compound {Fe(pyrazine)[Pt(CN)(4)]} shows that the switching of the rotation of a molecular fragment--the pyrazine ligand--occurs in association with the change of spin state. The rotation switching was examined on a wide time scale (10(-13)-10(-3) s) by both techniques, which clearly demonstrated the combination between molecular rotation and spin-crossover transition under external stimuli (temperature and chemical). The pyrazine rings are seen to perform a 4-fold jump motion about the coordinating nitrogen axis in the high-spin state. In the low-spin state, however, the motion is suppressed, while when the system incorporates benzene guest molecules, the movements of the system are even more restricted.     

线接触弹性流体动力润滑的供油条件分析

以油膜起始位置为参数,求出了等温线接触弹性流体动力润滑问题的完全数值解.通过流量分析,建立了有效供油膜厚与油膜起始位置之间的关系.结果表明,弹性流体动力润滑的供油方式可划分为过量供油、适量供油和乏油3种类型.在过量供油条件下大部分润滑油不能进入接触区,因而并不能改善润滑状态.在适量供油条件下所有润滑油均可通过接触区并能够获得最大的油膜厚度.在乏油条件下所有的润滑油也均可以通过接触区,而油膜厚度则完全由供油量确定.同时,数值结果也指出,只要运动表面存有数量级为1 μm厚的一层油液就足以满足适量供油条件而得到最佳的润滑效果.