Long-Range Transport in an Assembly of ZnO Quantum Dots: The Effects of Quantum Confinement,Coulomb Repulsion and Structural Disorder

We have studied the storage and long-range transport of electrons in a porous assembly of weakly coupled ZnO quantum dots permeated with an aqueous and a propylene carbonate electrolyte solution. The number of electrons per ZnO quantum dot is controlled by the electrochemical potential of the assembly; the charge of the electrons is compensated by ions present in the pores. We show with optical and electrical measurements that the injected electrons occupy the S, P, and D type conduction electron levels of the quantum dots; electron storage in surface states is not important. With this method of three-dimensional charge compensation, up to ten electrons per quantum-dot can be stored if the assembly is permeated with an aqueous electrolyte. The screening of the electron charge is less effective in the case of an assembly permeated with a propylene carbonate electrolyte solution. Long-range electron transport is studied with a transistor set-up. In the case of ZnO assemblies permeated with an aqueous electrolyte, two quantum regimes are observed corresponding to multiple tunnelling between the S orbitals (at a low occupation) and P orbitals (at a higher occupation). In a ZnO quantum-dot assembly permeated with a propylene carbonate electrolyte solution, there is a strong overlap between these two regimes.     

Reactivity of vinylamine radical cation with neutral dienes

The gas-phase ion—molecule reactions between ionized vinylamine ([CH₂ ? CHNH₂]^+.) as a set of conjugated and unconjugated dienes were studied by Fourier transform is observed. Conjugated dienes lead to the elimination of NH₃ or of an hydrocarbon radical from the adduct [M + CH₂ ? CHNH₂]^+.. In the case of unconjugated dienes a regiospecific cyclobutanation-cycloreversion process is observed. Reaction mechanisms are proposed to explain these experimental findings.     

121Sb Mössbauer spectral and related studies on Sb(III) complexes

The bonding and structural features of antimony(III) complexes of the type, (PrⁱO)SbL and Sb₂L₃ are described (where L is the dianion of semicarbazone or thiosemicarbazone). The Mössbauer spectra are typical of Sb(III) complexes in which the non-bonding pair of electrons is stereochemically active. The thiosemicarbazone complexes show more negative isomer shifts compared to the semicarbazone complexes.     

Stochastic Dynamics of Discrete Curves and Multi-Type Exclusion Processes

This study deals with continuous limits of interacting one-dimensional diffusive systems, arising from stochastic distortions of discrete curves with various kinds of coding representations. These systems are essentially of a reaction-diffusion nature. In the non-reversible case, the invariant measure has in general a non Gibbs form. The corresponding steady-state regime is analyzed in detail, by using a tagged particle together with a state-graph cycle expansion of the probability currents. As a consequence, the constants appearing in Lotka–Volterra equations—which describe the fluid limits of stationary states—can be traced back directly at the discrete level to tagged particle cycles coefficients. Current fluctuations are also studied and the Lagrangian is obtained via an iterative scheme. The related Hamilton–Jacobi equation, which leads to the large deviation functional, is investigated and solved in the reversible case, just for the sake of checking.     

Synthesis and Properties of First and Second Generation Chiral Dendrimers with Triply Branched Units: A Spectacular Case of Diastereoselectivity

Chiral triols (which may be considered as derivatives of tris(hydroxymethyl)methane), without ( 3-5 ) and with aliphatic ( 6 ) or aromatic ( 7 ) elongating units, and the 1st- and 2nd-generation benzylic branched bromides, 17, 18, 23, 24, 29 , and 30 are subjected to Williamson etherification conditions (NaH in THF). This gave the first ‘fully chiral’ dendrimers, with triple branching and with a stereogenic center at each and every branching point (including the central building block: see 33-42 , 44 , and 46-49 ). Higher than 2nd-generation dendrimers of this type could not be prepared. Certain combinations of diastereoisomeric 2nd-generation branched bromides, 23, 24, 29 , and 30 , and enantiomeric center-piece triols, 3 and 4 , would smoothly react to give the desired dendrimers (e.g., 44 , and 46-49 ) and others would not, with the reactions stopping at the dendritic alcohols containing only two branches (e.g., 45 , and 50-53 ; see Schemes 4 and 5). Considering the distance at which the intermediate diastereoisomeric ‘doubly coupled’ dendritic alcohols differ in their configuration, this diastereodifferentiation or molecular recognition phenomenon (discovered by trying to prepare only 8 out of 2³⁹ possible diastereoisomers!) is a most surprising result. All compounds were fully characterized, and the 2nd-generation dendrimers, e.g., 38 , 40 , and 47 with and without elongation were shown to be monodisperse and without defects, by MALDI-TOF mass spectroscopy (cf. Fig. 4). A simple, unambiguous nomenclature for identification of the novel dendritic compounds is proposed and applied in the Exper. Part.