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171.
Siebert R Winter A Schubert US Dietzek B Popp J 《Physical chemistry chemical physics : PCCP》2011,13(4):1606-1617
Temperature dependent luminescence experiments are combined with femtosecond time-resolved transient absorption spectroscopy to decipher the photoinduced excited-state relaxation pathway in mononuclear Fe, Ru and Os terpyridine complexes bearing a conjugated chromophore within the ligand framework. The herein presented complexes constitute a class of coordination compounds, which overcome the poor emission properties commonly observed for most terpyridine transition metal complexes. As reported earlier, the complexes reveal dual emission at room temperature stemming from ligand centered and metal-to-ligand charge-transfer states. The molecular mechanism of the room temperature dual luminescence is addressed experimentally in this contribution. The experimental results indicate an ultrafast branching reaction within the excited-state manifold upon photoexcitation of the ligand-centered S(1) state. This branching occurs from a "hot" excited state geometry close to the Franck-Condon point of absorption and within ~100 fs, i.e. the temporal resolution of our experimental setup. The combination of ultrafast differential absorption experiments and temperature-dependent luminescence data allows not only to draw conclusions about the molecular mechanism underlying the observed dual emission but also to construct quantitative Jablonski diagrams and, thereby, to detail the excited-state topology determining the remarkable luminescence properties of the systems at hand. 相似文献
172.
Zinad DS Shaaban KA Abdalla MA Islam MT Schüffler A Laatsch H 《Natural product communications》2011,6(1):45-48
Four isocoumarins have been isolated from the terrestrial Streptomyces sp. ANK302, namely 6,8-dimethoxy-3-methylisocoumarin (1), 6,8-dihydroxy-3-methylisocoumarin (2), 6,8-dihydroxy-7-methoxy-3-methylisocoumarin (3), and 6,7,8-trimethoxy-3-methylisocoumarin (4). Compound 1 is a new naturally-occurring isocoumarin, and 2 was isolated as a new bacterial product. The structures 1-4 were deduced from high resolution mass, 1D and 2D NMR spectra and by comparison with related compounds from the literature. Compound 2 showed a strong zoosporicidal activity at a concentration of 5 microg/mL against a phytopathogenic oomycete, Plasmopara viticola, and 1 was active against 相似文献
173.
This article presents a mathematical model describing flow of two fluid phases in a heterogeneous porous medium. The medium
contains disconnected inclusions embedded in the background material. The background material is characterized by higher value
of the non-wetting-phase entry pressure than the inclusions, which causes non-standard behavior of the medium at the macroscopic
scale. During the displacement of the non-wetting fluid by the wetting one, some portions of the non-wetting fluid become
trapped in the inclusions. On the other hand, if the medium is initially saturated with the wetting phase, it starts to drain
only after the capillary pressure exceeds the entry pressure of the background material. These effects cannot be represented
by standard upscaling approaches based on the assumption of local equilibrium of the capillary pressure. We propose a relevant
modification of the upscaled model obtained by asymptotic homogenization. The modification concerns the form of flow equations
and the calculation of the effective hydraulic functions. This approach is illustrated with two numerical examples concerning
oil–water and CO2–brine flow, respectively. 相似文献
174.
We outline the formalism of liquid integral equation theory for anisotropic interactions in two dimensions and subsequently apply this theory to one-component super-paramagnetic particles exposed to a tilted magnetic field. Inhomogeneous local ordering of the particles is observed for different in-plane directions. The anisotropy of the interaction as well as of the liquid structure is increased by increasing the tilt angle. Furthermore, the particles favour an alignment in the direction of the in-plane component of the magnetic field. For increasing tilt angle, the anisotropy of the structural correlations is qualitatively similar to that of the corresponding solid lattice which is stable at lower temperatures. However, the mean-square displacements behave qualitatively different in the solid and fluid phases as a function of the tilt angle. 相似文献
175.
In this work, we readdress the photoelectron spectra of the HM(CO)5, (M=Mn, Re) carbonyl complexes by applying four-component Fock-space coupled cluster (FSCC) methods for their calculation in order to extend earlier studies based on less demanding approaches. The final-state characterisation was based on group theoretical considerations of the contributing orbitals and allowed for an unambiguous assignment. Energy level diagrams show the effect of spin–orbit (SO) coupling starting from scalar relativistic results and for the heavy representative HRe(CO)5 nonadditivity effects of SO and electron correlation can be observed requiring a consistent treatment of both contributions. 相似文献
176.
177.
Hartmut R. Schwetlick 《Journal of Differential Equations》2002,179(1):356-368
We propose a hyperbolic generalisation of the well-known reaction diffusion equation and study the structure of its ω-limit sets. Under a dissipativity condition on the nonlinearity, we show quasi-convergence of the flow, saying that the ω-limit set of any orbit is non-empty, compact, connected, and contained in the set of equilibrium solutions. 相似文献
178.
179.
Rare-earth doped fibers suffer from relatively high attenuation in comparison to conventional communication fibers. In order to improve the properties of such fibers, understanding of the mechanisms involved in scattering effects is of great importance. The effect of Nd-doping, Al-codoping and of the drawing temperature on the scattering effect was investigated for several different optical fibers. To this end a measuring setup was realized which allows absolute measurements of the scattering coefficient at different positions along a fiber. Also separation of total attenuation and scattering effects is possible. The presented results indicate scattering effects as primary source for increased attenuation compared with undoped fibers. 相似文献
180.