Fluorescent Properties of a Hybrid Cadmium Sulfide-Dendrimer Nanocomposite and its Quenching with Nitromethane

A fluorescent hybrid cadmium sulphide quantum dots (QDs) dendrimer nanocomposite (DAB-CdS) synthesised in water and stable in aqueous solution is described. The dendrimer, DAB-G5 dendrimer (polypropylenimine tetrahexacontaamine) generation 5, a diaminobutene core with 64 amine terminal primary groups. The maximum of the excitation and emission spectra, Stokes’ shift and the emission full width of half maximum of this nanocomposite are, respectively: 351, 535, 204 and 212 nm. The fluorescence time decay was complex and a four component decay time model originated a good fit (χ = 1.20) with the following lifetimes: τ ₁ = 657 ps; τ ₂ = 10.0 ns; τ ₃ = 59.42 ns; and τ ₄ = 265 ns. The fluorescence intensity of the nanocomposite is markedly quenched by the presence of nitromethane with a dynamic Stern-Volmer constant of 25 M⁻¹. The quenching profiles show that about 81% of the CdS QDs are located in the external layer of the dendrimer accessible to the quencher. PARAFAC analysis of the excitation emission matrices (EEM) acquired as function of the nitromethane concentration showed a trilinear data structure with only one linearly independent component describing the quenching which allows robust estimation of the excitation and emission spectra and of the quenching profiles. This water soluble and fluorescent nanocomposite shows a set of favourable properties to its use in sensor applications.     

The Four Isomeric 1,3,5-Undecatrienes. Synthesis and configurational assignment

The four geometrical isomers of 1,3,5-undecatriene, 1a–d have been prepared (stereospecifically and non-stereospecifically), using either (1) the Wittig reaction, (2) thermal sigmatropic hydrogen shifts, (3) partial reduction of triple bonds by zinc, or (4) organocopper reagents. The thermal behaviour of the four 1,3,5-undecatrienes has been investigated and the products formed have been characterized. The spectra of 1a–d, and of related compounds, have been discussed in order to corroborate their configurational assignment.     

Synthesis and reactions of 2-aryl-3-(dimethylamino)acroleins

The preparation of a number of novel 2-aryl-3-(dimethylamino)acroleins and their hydrolyses to 2-arylmalondialdehydes is described. Reactions of the acroleins with amines are discussed as well as the conversion of the 2-arylmalondialdehydes into 3-chloro and 3-alkoxyacroleins.     

The convergence of the Rayleigh-Ritz Method in quantum chemistry

Two sufficient criteria for the convergence of the Rayleigh-Ritz Method (RRM) with respect to the eigenvalues (E-convergence) of non-relativistic electronic Hamiltonians of molecules are discussed and compared. Moreover, a necessary and sufficient criterion is given. By example (Sect. 9) it is shown that the L ²-completeness of the basis is not sufficient to guarantee E-convergence. The convergence of the wave functions in different norms (-convergence) is also investigated. In particular, sufficient conditions for the one-particle basis functions (orbitals) are given, such that a CI calculation in this basis is both E- and -convergent.     

Enaminosucres et sucres halogénoacétyléniques. Communication préliminaire

Enamino- and Halogenoacetylenic sugars Traitment of an aldehydosugar ( 1 ) with secondary amines gave in an essentially quantitative yield the expected enamines ( 4–6 ). Chloro- and bromo-acetylenic sugars ( 11–14 ) were obtained in good yields by reacting with lithium methylphenylamide the corresponding gem-dihalo-olefinic sugars ( 7–10 ), whereas a Z-gem-fluoro-enamine ( 17 ) was formed when the difluoro-olefinic sugar 15 was submitted to the same reaction. The fluoro-enamine 17 is a useful synthetic intermediate allowing the preparation of several kinds of C-glycosylic compounds bearing heterocycles like isoxazole, chromone or coumarin.