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41.
Katan C Terenziani F Mongin O Werts MH Porrès L Pons T Mertz J Tretiak S Blanchard-Desce M 《The journal of physical chemistry. A》2005,109(13):3024-3037
To investigate the effect of branching on linear and nonlinear optical properties, a specific series of chromophores, epitome of (multi)branched dipoles, has been thoroughly explored by a combined theoretical and experimental approach. Excited-state structure calculations based on quantum-chemical techniques (time-dependent density functional theory) as well as a Frenkel exciton model nicely complement experimental photoluminescence and one- and two-photon absorption findings and contribute to their interpretation. This allowed us to get a deep insight into the nature of fundamental excited-state dynamics and the nonlinear optical (NLO) response involved. Both experiment and theory reveal that a multidimensional intramolecular charge transfer takes place from the donating moiety to the periphery of the branched molecules upon excitation, while fluorescence stems from an excited state localized on one of the dipolar branches. Branching is also observed to lead to cooperative enhancement of two-photon absorption (TPA) while maintaining high fluorescence quantum yield, thanks to localization of the emitting state. The comparison between results obtained in the Frenkel exciton scheme and ab initio results suggests the coherent coupling between branches as one of the possible mechanisms for the observed enhancement. New strategies for the rational design of NLO molecular assemblies are thus inferred on the basis of the acquired insights. 相似文献
42.
Christine O. Paul-Roth Jean-Marie Lehn Jean Guilhem Claudine Pascard 《Helvetica chimica acta》1995,78(8):1895-1903
The crystal structure of the macrobicyclic europium(III) complex [Eu3+ ? 1 ]3Cl? incorporating a N,N′ - dioxide unit has been determined. It confirms the cryptate nature of this species, the included cation being bound to six N- and two O-sites. The efficient shielding of the bound Eu3+ ion may be related to the efficient luminescence of this cryptate and points to the role played by the N-oxide sites. To further explore the effect of such binding groups, the two macrocyclic ligands 4 and 5 bearing two bipyridine N,N′ -dioxide lateral arms have been synthesized and their EuIII and TbIII complexes prepared. 相似文献
43.
The complex structure of flax fibres involves many chemical biomolecules located in an amorphous matrix in which cellulose micrifibrils are embbeded. The drying of flax fibres influences significantly their tensile strength. This result can be explained by the creation of damages within the fibre and by the modification of the chemical composition of the matrix components. This loss of water involves a modification of the adhesion between the cellulose microfibrils and the matrix. This modification is due to the evolution of the components ensuring the transfer of load between the microfibrils and thus conditioning the strength of the cellular wall. 相似文献
44.
Claudine Devauchelle Andreas W. M. Dress Alexander Grossmann Stefan Grünewald Alain Henaut 《Annals of Combinatorics》2005,8(4):441-456
In this note, it is shown that by applying ranking procedures to data that allow, for any three objects a1, a2, b in a collection X of objects of interest, to make consistent decisions about which of the two objects a1 or a2 is more similar to b, a family of cluster systems
can be constructed that start with the associated Apresjan Hierarchy and keep growing until, for k = #X–1, the full set
of all subsets of X is reached. Various ideas regarding canonical modifications of the similarity values so that these cluster systems contain as many clusters as possible for small values of k (and in particular for k := 0) and/or are rooted at a specific element in X, possible applications, e.g. concerning (i) the comparison of distinct dissimilarity data defined on the same set X or (ii) diversity optimization, and new tasks arising in ranking statistics are also discussed.Received November 15, 2003 相似文献
45.
Epoxidation of 3β - Acetoxy - 7α - hydroxy - Δ14 - apotirucallane, prepared from Δ7-tirucallone, afforded the corresponding 14α,15α epoxide. The α-configuration of the epoxide function has been established by single-crystal X-ray analysis, representing the first such study of a tirucallol derivative with an intact side-chain. Epoxidation of Apotirucalla - 3,7 - dione gave the corresponding 14α,15α - epoxide as well. Eight new tirucallol derivatives were described. 相似文献
46.
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48.
Porrès L Mongin O Katan C Charlot M Pons T Mertz J Blanchard-Desce M 《Organic letters》2004,6(1):47-50
[structure: see text] Novel octupolar fluorophores derived from the symmetrical functionalization of a triphenylamine core with strong acceptor peripheral groups via phenylene-ethynylene linkers have been synthesized and shown to exhibit high fluorescence quantum yields, very large TPA cross-sections in the red-NIR region, and suitable photostability. 相似文献
49.
Claire Dubot Cyrille Allery Vincent Melot Claudine Bghein Mourad Oulghelou Clment Bonneau 《Entropy (Basel, Switzerland)》2021,23(10)
Predicting the void fraction of a two-phase flow outside of tubes is essential to evaluate the thermohydraulic behaviour in steam generators. Indeed, it determines two-phase mixture properties and affects two-phase mixture velocity, which enable evaluating the pressure drop of the system. The two-fluid model for the numerical simulation of two-phase flows requires interaction laws between phases which are not known and/or reliable for a flow within a tube bundle. Therefore, the mixture model, for which it is easier to implement suitable correlations for tube bundles, is used. Indeed, by expressing the relative velocity as a function of slip, the void fraction model of Feenstra et al. and Hibiki et al. developed for upward cross-flow through horizontal tube bundles is introduced and compared. With the method suggested in this paper, the physical phenomena that occur in tube bundles are taken into consideration. Moreover, the tube bundle is modelled using a porous media approach where the Darcy–Forchheimer term is usually defined by correlations found in the literature. However, for some tube bundle geometries, these correlations are not available. The second goal of the paper is to quickly compute, in quasi-real-time, this term by a non-intrusive parametric reduced model based on Proper Orthogonal Decomposition. This method, named Bi-CITSGM (Bi-Calibrated Interpolation on the Tangent Subspace of the Grassmann Manifold), consists in interpolating the spatial and temporal bases by ITSGM (Interpolation on the Tangent Subspace of the Grassmann Manifold) in order to define the solution for a new parameter. The two developed methods are validated based on the experimental results obtained by Dowlati et al. for a two-phase cross-flow through a horizontal tube bundle. 相似文献
50.
Jean-Marie Lehn Jean-Pierre Vigneron Itka Bkouche-Waksman Jean Guilhem Claudine Pascard 《Helvetica chimica acta》1992,75(4):1069-1077
The tris-carotenoid macrobicycles 1 and 2 were obtained in good yields in a one-step macrobicyclisation condensation between the tripode N(CH2CH2NH2)3 and the polyolefinic dialdehydes 5 and 6 . They form dinuclear cryptates by complexation of two CuI ions. The crystal structure of the tris-carotenoid compound 2 confirms that it contains three parallel polyolefinic strands. These substances may formally be considered as prototypes of molecular ‘cables’ formed by three electron-conducting molecular wires. 相似文献