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61.
Ein elektronenreiches cyclisches (Alkyl)(amino)carben auf Au(111)-, Ag(111)- und Cu(111)-Oberflächen
Anne Bakker Dr. Matthias Freitag Elena Kolodzeiski Peter Bellotti Dr. Alexander Timmer Dr. Jindong Ren Bertram Schulze Lammers Daniel Moock Prof. Dr. Herbert W. Roesky Dr. Harry Mönig Dr. Saeed Amirjalayer Prof. Dr. Harald Fuchs Prof. Dr. Frank Glorius 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(32):13745-13749
62.
Alexander S. Antonov Elena Yu Tupikina Valerii V. Karpov Valeriia V. Mulloyarova Victor G. Bardakov 《Molecules (Basel, Switzerland)》2020,25(24)
The influence of steric repulsion between the NMe2 group and a second ortho-(peri-)substituent in the series of 1-dimethylaminonaphthalene and N,N-dimethylanilene ortho-oximes on the ease of the NMe2 group’s intramolecular nucleophilic substitution is studied. Possible reaction intermediates for three mechanisms are calculated (ωB97xd/def-2-TZVP), and their free Gibbs energies are compared to model reaction profiles. Supporting experiments have proved the absence of studied reactivity in the case of simple 2-dimethylaminobenzaldoxime, which allowed us to establish reactivity limits. The significant facilitation of NMe2 group displacement in the presence of bulky substituents is demonstrated. The possibility of fused isoxazoles synthesis via the intramolecular nucleophilic substitution of a protonated NMe2 group in the aniline and naphthalene series is predicted. 相似文献
63.
Manon Catherin Olatz Uranga-Barandiaran Arnaud Brosseau Dr. Rémi Métivier Dr. Gabriel Canard Dr. Anthony D'Aléo Dr. David Casanova Prof. Frédéric Castet Dr. Elena Zaborova Prof. Frédéric Fages 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(17):3818-3828
We describe the synthesis of a series of covalently linked dimers of quadrupolar curcuminoid-BF2 dyes and the detailed investigation of their solvent-dependent spectroscopic and photophysical properties. In solvents of low polarity, intramolecular folding induces the formation of aggregated chromophores, the UV/Vis absorption spectra of which display the optical signature characteristic of weakly-coupled H-aggregates. The extent of folding and, in turn, of ground-state aggregation is strongly dependent on the nature of the flexible linker. Steady-state and time-resolved fluorescence emission spectroscopies show that the Frenkel exciton relaxes into a fluorescent symmetrical excimer state with a long lifetime. Furthermore, our in-depth studies show that a weakly emitting excimer lies on the pathway toward a photocyclomer. Two-dimensional 1H NMR spectroscopy and density functional theory (DFT) allowed the structure of the photoproduct to be established. To our knowledge, this represents the first example of a [2π+2π] photodimerization of the curcuminoid chromophore. 相似文献
64.
An analytical protocol consisting of X‐ray fluorescence spectroscopy, optical microscopy and Fourier transform infrared spectroscopy was used to study the origin and the nature of the materials (pigments, binders and coating preparation) of the Fundenii Doamnei church mural paint from Bucharest. The main interest of the present study consisted in the original votive paint from narthex, painted in 1757 in a secco technique. During analysis, an unexpected pigment in the votive paint could be detected by the combined analytical techniques: ultramarine blue. Along with this pigment, the presence of gypsum binder based on egg and flax seed oil could also be evidenced. These results demonstrated a secco execution technique of the votive paint and also the presence of a restoration treatment. Moreover, during the present study, the components of the preparation layer and the constitutive pigments from both 1699 and 1757 years mural paints have been analyzed. Hence, the following pigments could be identified: vermilion, azurite, cinnabar, lead white, ochre, natural umber and gold, by using the combination of the analytical techniques. The novelty of our results consists in detecting the composition of the materials used in this church painting (fresco and a secco) during these 254 years since its first restoration. The results of these investigations pointed to the suitability of the non‐destructive and semi‐destructive analytical techniques in the complex characterization of the paints realized in different techniques, at different periods. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
65.
Elena Bosetto Enrico Serra 《Annales de l'Institut Henri Poincaré (C) Analyse Non Linéaire》2000,17(6):673
We prove that a class of problems containing the classical periodically forced pendulum equation displays the main features of chaotic dynamics. The approach is based on the construction of multibump type heteroclinic solutions to periodic orbits by the use of global variational methods. 相似文献
66.
An investigation is reported of coherent resonance in the degenerate two-level system of the (Fg = 2 --> Fe = 1) transition of the 87Rb D1 line by means of a Hanle effect configuration. In a coherent population trapping experiment, a very narrow (approximately 1-kHz) resonance superimposed upon a broader resonance (approximately 100 kHz) was observed. The dependence of the width and the amplitude of the coherent resonance on the laser power density, on additional constant magnetic fields, on the laser frequency position along the fluorescence profile, and on Rb cells with different dimensions was investigated. 相似文献
67.
Petr A. Obraztsov Anatoliy. A. Sirotkin Elena D. Obraztsova Yuri P. Svirko Sergey V. Garnov 《Optical Review》2010,17(3):290-293
We demonstrate the passive mode-locking of a diode-pumped Nd+3:YAG (central wavelength: 1.32 μm; pulse duration: 50 ps; output energy: up to 70 μJ) laser using a polymer film containing
single-wall carbon nanotubes. The mode-locking regime is stable at a pump repetition rate of up to 1 kHz. We also investigate
the temporal evolution of the light-induced absorption change of the polymer film containing carbon nanotubes in the spectral
range of 1.3–1.5 μm by femtosecond time-resolved pump-probe measurements. The measurements reveal that light-induced transmission
exhibits fast and slow components that last 280 fs and more than 10 ps, respectively. The third-order susceptibility of the
polymer film containing single wall carbon nanotubes is as high as 10−11 esu. 相似文献
68.
In this paper we consider discrete-time positive switched systems, switching among autonomous subsystems, characterized either by monomial matrices or by circulant matrices. Necessary and sufficient conditions are provided guaranteeing either (global uniform) asymptotic stability or stabilizability (i.e. the possibility of driving to zero the state trajectory corresponding to any initial state by resorting to some switching sequence). Such conditions lead to simple algorithms that allow to easily detect, under suitable conditions, whether a given positive switched system is not stabilizable. 相似文献
69.
70.
Maria Gil Elena Bermejo Alfonso Castieiras Heloisa Beraldo Douglas X. West 《无机化学与普通化学杂志》2000,626(11):2353-2360
Pyridyl bis(N(4)‐substituted thiosemicarbazones), in which the substituents replacing the NH2 group on the thiosemicarbazone moieties are piperidyl, H2Plpip; hexamethyleneiminyl, H2Plhexim; diethylamino, H2Pl4DE; and dipropylamino, H2Pl4DP, have been synthesized. These bis(thiosemicarbazones) and their nickel(II) complexes have been characterized with IR, electronic, mass, and 1H and 13C NMR spectra. Crystal structures have been solved for H2Plpip and all four nickel(II) complexes. H2Plpip does not possess hydrogen bonding between the thiosemicarbazone moieties, but is in the Z isomeric form with intramolecular hydrogen bonding from both thiosemicarbazone moieties to pyridine nitrogen atoms. The nickel(II) complexes possess square‐planar N2S2 (i. e., imine nitrogen and thiolato sulfur atoms) centers and the two pyridine ring nitrogen atoms are not coordinated. 相似文献