Synthesis, characterisation and functionalisation of luminescent silica nanoparticles

The synthesis of highly monodispersed, homogeneous and stable luminescent silica nanoparticles, synthesized using a process based on the Stöber method is reported here. These particles have been functionalised with the ruthenium and europium complexes: bis (2,2??-bipyridine)-(5-aminophenanthroline) Ru bis (hexafluorophosphate), abbreviated to (Ru(bpy)₂(phen-5-NH₂)(PF₆)), and tris (dibenzoylmethane)-mono (5-aminophenanthroline) europium(III), abbreviated to (Eu:TDMAP). Both dyes have a free amino group available, facilitating the covalent conjugation of the dyes inside the silica matrix. Due to the covalent bond between the dyes and the silica, no dye leaching or nanoparticle diameter modification was observed. The generic and versatile nature of the synthesis process was demonstrated via the synthesis of both europium and ruthenium-functionalised nanoparticles. Following this, the main emphasis of the study was the characterisation of the luminescence of the ruthenium-functionalised silica nanoparticles, in particular, as a function of surface carboxyl or amino group functionalisation. It was demonstrated that the luminescence of the ruthenium dye is highly affected by the ionic environment at the surface of the nanoparticle, and that these effects can be counteracted by encapsulating the ruthenium-functionalised nanoparticles in a plain 15 nm silica layer. Moreover, the ruthenium-functionalised silica nanoparticles showed high relative brightness compared to the free dye in solution and efficient functionalisation with amino or carboxyl groups. Due to their ease of fabrication and attractive characteristics, the ruthenium-functionalised silica nanoparticles described here have the potential to be highly desirable fluorescent labels, particularly, for biological applications.     

Extending Excited-state Lifetimes by Interchromophoric Triplet-state Equilibration in a Pyrene-Ru(II)diimine Dyad System

The synthesis and the spectroscopic properties of a bichromophoric ruthenium trisbipyridyl-1,4-diethynylenebenzene-pyrene system (Ru-b-Py) and the corresponding pyrene ligand (b-Py) are reported. The ruthenium model systems Ru-b-OH, Ru-b-Ph are also presented. UV–Vis absorption and emission at room and low temperature and time-resolved spectroscopy are discussed. For the Ru-b-Py dyad, a mixing of the ³MLCT state of the ruthenium-based component and the triplet state of pyrene, ³Py, is observed. Time-resolved transient absorption studies performed on the Ru-b-Py and on the b-Py ligand show that the lowest energy absorption is due to the population of the triplet state localized on the pyrene-component. Time-resolved studies also evidenced a relatively slow forward triplet equilibration rate, in the order of 2×10⁵?s^-1 (5?μs), and an even slower back energy transfer rate, 3.3×10⁴?s^-1, still faster than the intrinsic decay time of the pyrene (200?μs).     

Cyclopropanotetrahydropyridines

In recent syntheses of eburnamonine,¹ aspidospermidine² and quebrachamine² the copper-catalyzed, diazoacetic ester-induced conversion of tetrahydropyridine 1 into the cyclopropanopiperidine 2 was a crucial, early reaction step. It became of interest to apply this reaction to dihydropyridine equivalents of 1, i.e. 3 and 4, in connection with the development of routes of synthesis directed towards alkaloids of the pandoline or velbenamine types. This Communication illustrates the preparation and cyclopropanation of dihydropyridines 3 and 4.     

Fonctions Properes Sur Des Variétés Avec Des Anses Fines,Applcation À La Multiplicité

We present here some results on the behaviour of the eigenfunctions of the Laplace operator under a singular perturbation obtained by adding a thin handle to a compact manidold X¹ it follows the work [A] where the convergence of the spectrum was probed. We restrict ourselves to the dimension 2, and the can show a result concerning inverasing multiplcity (theorem 2) : if is a eingenvalue of X¹, with multiplicity m, which is assumed to be stable (the SAH notion introduced by Colin de Verdiè in [CdV]), and if we denot by E⁰ the Corresponding eigenspace then for any pari (p, q) of points on X¹ for which one of these two linear forms vanishes identically on E⁰ we can attach a thin handle to X¹ on connecting p and q so that the resulting manifold has as an eigenvalue with multiplicity (m + 1), for a family of metrics to the original one X¹     

Integration of Technology in the Design of Geometry Tasks with Cabri-Geometry

Beginning with the gap in France between the institutional support for the use of technology in mathematics teaching and its weak integration into teacher practice, this paper claims that integrating technology into teaching is a long process. The aim of the paper is to identify and analyse the steps in this integration using as an example the evolution over time (3 years) in the design of teaching scenarios based on Cabri-géomètre for high school students. The analysis indicates that the role played by the technology moved from being a visual amplifier or provider of data towards being an essential constituent of the meaning of tasks and as a consequence affected the conceptions of the mathematical objects that the students might construct.This revised version was published online in September 2005 with corrections to the Cover Date.