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351.
Fabian Hundemer Lorenz Graf von Reventlow Céline Leonhardt Mika Polamo Martin Nieger Stefan M. Seifermann Alexander Colsmann Prof. Dr. Stefan Bräse 《ChemistryOpen》2019,8(12):1413-1420
We demonstrate modular modifications of the widely employed emitter 2,4,5,6-tetra(9H-carbazol-9-yl)isophthalonitrile (4CzIPN) by replacing one or both nitrile acceptors with oxadiazole groups via a tetrazole intermediate. This allows the introduction of various functional groups including halides, alkynes, alkenes, nitriles, esters, ethers and a protected amino acid while preserving the thermally activated delayed fluorescence (TADF) properties. The substituents control the emission maximum of the corresponding emitters, ranging between 472–527 nm, and show high solid-state photoluminescence quantum yields up to 85 %. The TADF emission of two compounds, 4CzCNOXDtBu and 4CzdOXDtBu, a mono- and a bis-oxadiazole substituted 4CzIPN is characterized in detail by time- and temperature-dependent photoluminescence. Solution-processed OLEDs comprising 4CzCNOXDtBu and 4CzdOXDtBu show a significant blue-shift of the emission compared to the reference 4CzIPN, with external quantum efficiencies of 16 %, 5.9 % and 17 % at 100 cd m−2, respectively. 相似文献
352.
Oxygen transfer from sulfoxides: selective oxidation of alcohols catalyzed by polyoxomolybdates 总被引:1,自引:0,他引:1
Benzylic, allylic, and aliphatic alcohols are oxidized to aldehydes and ketones in a reaction catalyzed by Keggin-type polyoxomolybdates, PV(x)Mo(12-x)O(40)(-(3+x)) (x = 0, 2), with DMSO as a solvent. The oxidation of benzylic alcohols is quantitative within hours and selective, whereas that of allylic alcohols is less selective. Oxidation of aliphatic alcohols is slower but selective. Further mechanistic studies revealed that, for H(3)PMo(12)O(40) as a catalyst and benzylic alcohols as substrates, the sulfoxide is in fact an oxygen donor in the reaction. Postulated reaction steps as determined from isotope-labeling experiments, kinetic isotope effects, and Hammett plots include (a) sulfoxide activation by complexation to the polyoxometalate and (b) oxygen transfer from the activated sulfoxide and elimination of water from the alcohol. The mechanism is supported by the reaction kinetics. 相似文献
353.
In this paper we study the formal algebraic structure underlying the intrinsic classification algorithm, recently introduced in Singer et al. (SIAM J. Imaging Sci. 2011, accepted), for classifying noisy projection images of similar viewing directions in three-dimensional cryo-electron microscopy (cryo-EM). This preliminary classification is of fundamental importance in determining the three-dimensional structure of macromolecules from cryo-EM images. Inspecting this algebraic structure we obtain a conceptual explanation for the admissibility (correctness) of the algorithm and a proof of its numerical stability. The proof relies on studying the spectral properties of an integral operator of geometric origin on the two-dimensional sphere, called the localized parallel transport operator. Along the way, we continue to develop the representation theoretic set-up for three-dimensional cryo-EM that was initiated in Hadani and Singer (Ann. Math. 2010, accepted). 相似文献
354.
355.
J. W. Leonhardt H.-J. Große P. Popp 《Isotopes in environmental and health studies》2013,49(11):352-358
Die Ionisationsgasanalyse ist eine gasanalytische Methode, die anf der Änderung der durch Ionisation von Atomen oder Molekülen hervorgerufenen Leitfähigkeit von Gasen beruht. Ausgehend von einer allgemeinen Charakterisierung der anf diesem Verfahren basierenden Ionisationsdetektoren (Elektroneneinfang-, Aerosolionisations-, Ionisierungsquerschnitts und Edelgasdetektoren) werden deren Theorie, Eigenschaften, Hauptanwendungsgebiet und Entwicklungsmöglichkeiten aufgezeigt und diskutiert. 相似文献
356.
The application of numerical methods for the calculation of the molecular weight distribution of living ionic polymerization, carried out in the presence of monofunctional and polyfunctional transfer agents, is described. The methods used include the numerical solution of a system of differential equations by the Runge-Kutta-Merson procedure and the statistical Monte-Carlo approach. When a monofunctional transfer agent is used, the Runge-Kutta-Merson procedure is quite useful for the calculation of the molecular weight distribution for various polymerization systems. When a polymerization is carried out in the presence of a polyfunctional transfer agent, the mechanism includes the coupling of polymer chains. Due to the complexity of the system, the Runge-Kutta-Merson procedure is hardly applicable and problems of this type should be solved by a Monte Carlo simulation procedure. Once a computer program has been written, both methods allow the chemist to calculate the molecular weight distribution of a polymer as a function of the different kinetic parameters of the polymerization. 相似文献
357.
A. Leonhardt D. Selbmann E. Wolf M. Schnherr C. Herrmann 《Crystal Research and Technology》1978,13(5):523-529
Monocrystalline layers of n-type 3C–SiC are deposited by the thermal decomposition of SiCl4 and CCl4 in the hydrogen flow on commercial p-type 6H–SiC on 1750°C. The morphologies of the deposits are described in dependence on the deposition rate. The EPD values are observed between 6.3 × 102 and 3.4 × 103 cm−2. Stacking faults and microtwins in the (111)-plane are detected. 相似文献
358.
359.
H. Rentsch G. Kühn A. Leonhardt V. Gottschalch E. Butter 《Crystal Research and Technology》1976,11(2):133-139
The pseudoternary cut Sn GaAs GaP of the quarternary system Ga As P Sn has been investigated in a temperature range from 860 to 1200°C. The calculation based on Vieland's method by use of Darken's quadratic formalism. A comparision between the solvents tin and gallium shows a higher solubility in tin for the mixed crystal GaxPAs1−x and a stronger variation of the composition along the growth direction. 相似文献
360.
Recently, a scaled boundary finite element (SBFE) formulation for geometrically and physically nonlinear materials has been developed using the scaled boundary finite element method (SBFEM). The SBFE formulation has been employed to describe plane stress problems of notched and unnotched hyperelastic elastomer specimens. In this contribution, the derived SBFE formulation is extended to nonlinear time- and temperature-dependent material behavior. Subsequently, the SBFE formulation is incorporated into a crack propagation scheme to model crack propagation in cyclically loaded elastomer specimens of the so-called tear fatigue analyzer (TFA). (© 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献