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排序方式: 共有427条查询结果,搜索用时 343 毫秒
421.
The possibility to modulate molecules reversibly by light has been fascinating chemists early on. One of the most powerful photochromic classes of compounds are azobenzenes, which have been incorporated in multiple molecular systems to alter their functionality. Recently, the incorporation of azobenzenes into macrocyclic scaffolds, azobenzenophanes, revealed a novel aspect of this interesting photoswitch. Especially, the build-in of more than one azobenzene moiety into the structure creates photochromic compounds with multiple accessible states. The cyclic arrangement also leads to a change in the photochemical properties, which offer new opportunities for functional molecular devices. In this article the synthesis as well as the photochemistry including applications of macrocyclic azobenzenes, containing more than one azobenzene unit, oligoazobenzenophanes, are reviewed. 相似文献
422.
A chiral cyclotrisazobiphenyl macrocycle was synthesized conveniently in three steps from the literature known 3,3'-diaminobimesityl in 37-38% overall yield. Irradiation with 302 nm, 365 nm or visible light allows access to different photostationary states (PSSs). These PSSs can be conveniently read out by CD-spectroscopy as each of them exhibits a positive, a negative, or no signal, respectively, at 275 nm. 相似文献
423.
424.
Abstract The title compound Et2SnCl2 · H2O was prepared and characterized by IR-spectroscopy and single crystal X-ray diffraction, showing the typical trigonal bipyramidal structure of a SN2 transition state with the water molecule in an axial position. Supplemental materials are available for this article. Go to the publisher's online edition of Phosphorus, Sulfur, and Silicon and the Related Elements to view the free supplemental file. GRAPHICAL ABSTRACT 相似文献
425.
Reuter S Hofmann AM Busse K Frey H Kressler J 《Langmuir : the ACS journal of surfaces and colloids》2011,27(5):1978-1989
Langmuir films of multifunctional, hydrophilic polyethers containing a hydrophobic cholesterol group (Ch) were studied by surface pressure-mean molecular area (π-mmA) measurements and Brewster angle microscopy (BAM). The polyethers were either homopolymers or diblock copolymers of linear poly(glycerol) (lPG), linear poly(glyceryl glycidyl ether) (lPGG), linear poly(ethylene glycol) (lPEG), or hyperbranched poly(glycerol) (hbPG). Surface pressure measurements revealed that the homopolymers lPG and hbPG did not stay at the water surface after spreading and solvent evaporation, in contrast to lPEG. Because of the incorporation of the Ch group in the polymer structure, stable Langmuir films were formed by Ch-lPG(n), Ch-lPGG(n), and Ch-hbPG(n). The Ch-hbPG(n), Ch-lPEG(n), Ch-lPEG(n)-b-lPG(m), Ch-lPEG(n)-b-lPGG(m), and Ch-lPEG(n)-b-hbPG(m) systems showed an extended plateau region assigned to a phase transition involving the Ch groups. Typical hierarchically ordered morphologies of the LB films on hydrophilic substrates were observed for all Ch-initiated polymers. All LB films showed that Ch of the Ch-initiated homopolymers is able to crystallize. This strong tendency of self-aggregation then triggers further dewetting effects of the respective polyether entities. Fingerlike morphologies are observed for Ch-lPEG(69), since the lPEG(69) entity is able to undergo crystallization after transfer onto the silicon substrate. 相似文献
426.
Azobenzenes have attracted great interest in recent years because of their ability to change conformation upon irradiation. This property has been featured in several applications not only in organic chemistry but also in biology. Even though monoazobenzenes have been extensively studied and documented in the literature, only a few methods are available for the synthesis of oligo-ortho-azobenzenes. Also, their photochemical properties have not been reported so far. This study shows an efficient strategy for the preparation of oligo-ortho-azobenzenes and the investigation of their photochemical properties. It is demonstrated that the absorption spectra are highly influenced by the substituents. Interestingly, none of the ortho-bis-, tris-, or tetra-azobenzenes showed any E → Z isomerization. Only the ortho-nitrogen-substituted monoazobenzenes' photochromic behavior upon UV irradiation was observed. 相似文献
427.
Alessandro Ballestrero Benedikt Biedermann Simon Brass Ansgar Denner Stefan Dittmaier Rikkert Frederix Pietro Govoni Michele Grossi Barbara Jäger Alexander Karlberg Ezio Maina Mathieu Pellen Giovanni Pelliccioli Simon Plätzer Michael Rauch Daniela Rebuzzi Jürgen Reuter Vincent Rothe Christopher Schwan Hua-Sheng Shao Pascal Stienemeier Giulia Zanderighi Marco Zaro Dieter Zeppenfeld 《The European Physical Journal C - Particles and Fields》2018,78(8):671
Vector-boson scattering processes are of great importance for the current run-II and future runs of the Large Hadron Collider. The presence of triple and quartic gauge couplings in the process gives access to the gauge sector of the Standard Model (SM) and possible new-physics contributions there. To test any new-physics hypothesis, sound knowledge of the SM contributions is necessary, with a precision which at least matches the experimental uncertainties of existing and forthcoming measurements. In this article we present a detailed study of the vector-boson scattering process with two positively-charged leptons and missing transverse momentum in the final state. In particular, we first carry out a systematic comparison of the various approximations that are usually performed for this kind of process against the complete calculation, at LO and NLO QCD accuracy. Such a study is performed both in the usual fiducial region used by experimental collaborations and in a more inclusive phase space, where the differences among the various approximations lead to more sizeable effects. Afterwards, we turn to predictions matched to parton showers, at LO and NLO: we show that on the one hand, the inclusion of NLO QCD corrections leads to more stable predictions, but on the other hand the details of the matching and of the parton-shower programs cause differences which are considerably larger than those observed at fixed order, even in the experimental fiducial region. We conclude with recommendations for experimental studies of vector-boson scattering processes. 相似文献