Emission secondaire de petits agregats NipCn par des carbures de nickel

The intensities of emission of Ni_pC_n⁺(p = 1–3) and NiC_n^? secondary ions given by two alloys: Ni₃C and NiC 5% at. C, show off a saw-toothed behaviour according to the parity of the number n of carbon atoms. Maxima occur when n is odd for NiC_n⁺ ions and when n is even in the other cases (p = 2, 3; negative ions). Besides, the influence of the carbon concentration in the alloy can be observed.The alternations of NiC_n⁺ and Ni₂C_n⁺ ions can be interpreted from Pitzer and Clementi model (the clusters are supposed to be linear). Thus it can be found greater stabilities for NiC_2k+1 and Ni₂C_2k chains than for NiC_2k and Ni₂C_2k+1 chains respectively, which very well agrees with the “correspondence rule” between the emissions of different species of ions and their electronic properties.     

Enhanced two-photon absorption with novel octupolar propeller-shaped fluorophores derived from triphenylamine

[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.     

Colour coding the co-conformations of a [2]rotaxane flip-switch

Fine-tuning the charge transfer chromophores in a series of [2]rotaxane flip-switches yields a unique optical signal (purple colour) for one of the interactions allowing for facile determination of the position of the flip-switch equilibrium.     

From Graftable Biphotonic Chromophores to Water‐Soluble Organic Nanodots for Biophotonics: The Importance of Environmental Effects

The photophysical and two‐photon absorption (TPA) properties of biphotonic chromophores with one or two phenol pendant units were studied and compared with that of a model biphotonic quadrupolar chromophore. A water‐soluble dendritic structure was then synthesized by using the pendant moieties as starting points for the construction of dendritic branches. We show that the polarity of the environment significantly modulates both the fluorescence and the TPA responses of the different chromophoric derivatives. This extends to more subtle effects that involve phenol pendant moieties that were found to act as discrete solvating units and to modify both the photophysics and the TPA response of the chromophore. This demonstrates the high sensitivity of the TPA response of quadrupolar derivatives to minute alterations in the environment. Moreover, the dendritic branches were found to behave as a peculiar cybotactic environment that was able to tune the fluorescence and TPA response of the inner chromophore by creating a polar environment. This reveals a new direction for exploiting such effects by playing on the dendritic architecture (e.g., the nature and shape of the building blocks, the geometry and position of the chromophore) to modulate the TPA responses.     

Enzymatic resolution of 3-bromo-cyclohept-2-enol: application to the determination of the absolute configuration of diethyl (3-hydroxy-cyclohept-1-enyl)phosphonate

Enzymatic resolution of racemic 3-bromo-cyclohept-2-enol 2 with lipozyme affords enantiomerically pure (S)-(−)-2 whose absolute configuration was determined by chemical correlation, and further allowed an enantioselective synthesis of (S)-(+)-diethyl (3-hydroxy-cyclohept-1-enyl)phosphonate 1.     

Local Existence of Analytical Solutions to an Incompressible Lagrangian Stochastic Model in a Periodic Domain

We consider an incompressible kinetic Fokker Planck equation in the flat torus, which is a simplified version of the Lagrangian stochastic models for turbulent flows introduced by S.B. Pope in the context of computational fluid dynamics. The main difficulties in its treatment arise from a pressure type force that couples the Fokker Planck equation with a Poisson equation which strongly depends on the second order moments of the fluid velocity. In this paper we prove short time existence of analytic solutions in the one-dimensional case, for which we are able to use techniques and functional norms that have been recently introduced in the study of a related singular model.     

Two‐Photon Polarity Probes Built from Octupolar Fluorophores: Synthesis,Structure–Properties Relationships,and Use in Cellular Imaging

A series of octupolar fluorophores built from a triphenylamine (TPA) core connected to electron‐withdrawing (EW) peripheral groups through conjugated spacers has been synthesized. Their photoluminescence, solvatochromism, and two‐photon absorption (2PA) properties were systematically investigated to derive structure–property relationships. All derivatives exhibit two 2PA bands in the 700–1000 nm region: a first band at low energy correlated with a core‐to‐periphery intramolecular charge transfer that leads to an intense 1PA in the blue‐visible range, and a second more intense band at higher energy due to an efficient coupling of the branches through the TPA core. Increasing the strength of the EW end groups or the length of the conjugated spacers and replacing triple‐bond linkers with double bonds induces both enhancement and broadening of the 2PA responses, thereby leading to cross‐sections up to 2100 GM at peak and higher than 1000 GM over the whole 700–900 nm range. All derivatives exhibit intense photoluminescence (PL) in low‐ to medium‐polarity environments (with quantum yields in the 0.5–0.9 range) and display a strong positive solvatochromic behavior (with Lippert–Mataga specific shifts ranging from 15 000 to 27 500 cm^?1), triple bonds, and phenyl moieties in the conjugated spacers, thereby leading to larger sensitivities than those of double bonds and thienyl moieties. More hydrophilic derivatives were also shown to be biocompatible, to retain their 2PA and PL properties in biological conditions, and finally to be suitable as polarity sensors for multiphoton cell imaging.     

Local electrochemical impedance spectroscopy: A window into heterogeneous interfaces

The ability to probe surface reactivity on a local scale has led to a new insight into the comprehension of the electrochemical reactivity in relation with the microstructure of the surface. Among the different techniques developed in recent years, local electrochemical impedance spectroscopy has the advantage of using a transient approach to locally characterize a stationary electrochemical system without the need to add any redox mediator in solution, which is a great advantage for the study of different systems.In this review, particular attention is paid to the different ways of measuring the local impedance, and the technique implementing a local current measurement in solution is deeply discussed. This local electrochemical impedance spectroscopy journey also encompasses a discussion about technical and experimental limitations.