Vinylmercury Hydrides: Synthesis and Spectroscopic Characterization

The first vinylmercury hydrides, and among them the parent compound, have been prepared by a chemoselective reduction of the corresponding vinylmercury chlorides with tributylstannane in the presence of a radical inhibitor. These hydrides have been characterized on the basis of their spectral data ((1)H, (13)C, and (199)Hg NMR spectroscopy and mass spectrometry). The photoelectron spectra of the ethenylmercury hydride displays bands at 9.79, 10.13, 11.41, and 13.20 eV. On the basis of photoelectron spectra and ab initio quantum chemical calculations some (d-p)pi interaction between the vinyl pi-system and the mercury d-orbitals could be concluded. Vinylmercury hydrides have been condensed and then revaporized in vacuum at low temperature, but they exhibit a very low stability at room temperature even diluted in toluene (tau(1/2) approximately 1 min); elemental mercury and the corresponding divinylmercury were formed under these conditions.     

Structure de la cis-dihydroxy-4,5 diphényl-3,4 méthyl-5 isoxazoline-2

The structure of cis 4,5-dihydroxy-3,4-diphenyl-5-methyl-2-isoxazoline has been determined from the X ray crystallographic analysis. The results show the non-planarity of the isoxazoline ring and the presence of intra- and intermolecular hydrogen bonding.     

Propriétés de la benzopyranno[1][2,3-b]quinoxalinone-12

Under basic conditions. [1]benzopyrano[2,3-b]quioxakin-12-one leads to 3-(i-hydroxybenzoy1)-1H-quinoxalin-2-one. This ketone reacts with hydroxylamine and phenylhydrazine to give the expected derivatives or those of [1]benzopyrano92,3-b]quinoxalin-12-one. The reduction of [1]benzopyrano[2,3-b]quinoxalin-12-one was unsucessful by chemical means. However, electrochemical reduction leads to a dihydropyrazine nucleus.     

Synthèse,réduction chimique et électrochimique de benzopyranno[1][4,3-e] et [3,4-e]pyrimido[1,2-b]-as-triazinones

From 9H-amino [l]benzopyranno-as-triazines 2 and 3 , [l]ben-zopyranno[4,3-e] or [3,4-e]pyrimido[l,2-b]-as-triazinones have been prepared by reaction with β-ketoesters. Chemical reduction of the compounds gives tetrahydro derivatives. By electrochemical reduction the dihydro compounds 14 and 15 were from-ed. The same dihydro derivatives were obtained with Grignard reagents.     

Crown ether vinylogous tetrathiafulvalene receptors: complexation interference on the molecular movements triggered by electron transfer

The synthesis of a series of crown ether substituted vinylogous tetrathiafulvalenes (TTFVs) has been carried out through oxidative coupling of bisdithiafulvenes. These new receptors have been fully characterized using electrochemical, spectroelectrochemical, and molecular modeling experiments. These studies show that, upon oxidation, either a clip movement (TTFVs 3a,b) or a stretch movement (TTFV 3c) occurs, depending on the length of the crown ether chains. Preliminary electrochemical studies, undertaken on TTFV 3c in dichloromethane, show a little shift of the first standard oxidation potential toward more positive values upon addition of the Pb(2+) ion, but a considerable variation of the electron-transfer kinetics. This result introduces an interesting concept for the preparation of sensors not based on thermodynamic variations but on kinetic modifications of the electron transfer.     

Anomalous Light-Induced Spin-State Switching for Iron(II) Spin-Crossover Molecules in Direct Contact with Metal Surfaces

Light-induced spin-state switching is one of the most attractive properties of spin-crossover materials. In bulk, low-spin (LS) to high-spin (HS) conversion via the light-induced excited spin-state trapping (LIESST) effect may be achieved with a visible light, while the HS-to-LS one (reverse-LIESST) requires an excitation in the near-infrared range. Now, it is shown that those phenomena are strongly modified at the interface with a metal. Indeed, an anomalous spin conversion is presented from HS state to LS state under blue light illumination for Fe^II spin-crossover molecules that are in direct contact with metallic (111) single-crystal surfaces (copper, silver, and gold). To interpret this anomalous spin-state switching, a new mechanism is proposed for the spin conversion based on the light absorption by the substrate that can generate low energy valence photoelectrons promoting molecular vibrational excitations and subsequent spin-state switching at the molecule–metal interface.     

激光诱导击穿光谱应用于三种水果样品微量元素的分析

激光诱导击穿光谱(LIBS)在植物样品上面的应用是一个较新的课题. 为将LIBS技术能实际应用于与食品安全相关的领域,实验中对三种真空冻干水果样品进行了初步LIBS实验研究,鉴别了其LIBS光谱,并选取典型光谱线,运用统计学方法分析比较了三种水果中Ca,Na,K,Fe,Al,Mg六种元素含量的差别. 实验结果表明,苹果中Na的含量最高,Ca的含量最低,三种水果样品中的K,Fe,Mg等元素含量也都有差异. 实验结果还表明LIBS技术是一种检测、对比植物样品中微量元素含量的有效手段. 关键词： 激光诱导击穿光谱 等离子体 植物样品 微量元素     

Three-dimensional direct femtosecond laser writing of second-order nonlinearities in glass

We demonstrate that direct femtosecond laser writing in silver-containing zinc and gallium phosphate glass enables generation of three-dimensional (3D) optical second-order nonlinear microstructures having an χ(2) value about 2.5 times that of quartz. The proposed physical model involves photo-reduction, photo-dissociation, and migration of silver species within the glass matrix. 3D laser-written second-order nonlinear structures could become a new class of nonlinear optical components.     

一种新型的束流剖面探测系统

介绍了一种以微通道板和电阻阳极所构成的位置灵敏探测器为基础、用于兰州重离子加速器束流诊断的新型剩余气体电离束流剖面探测系统.描述了其工作原理、系统结构及初步实验结果,证明利用剩余气体电离束流剖面探测系统进行非拦截束流诊断的方法是可行的.