Search results for "Clusters"
showing 10 items of 1274 documents
Reactions with a Metalloid Tin Cluster {Sn10[Si(SiMe3)3]4}(2-): Ligand Elimination versus Coordination Chemistry.
2015
Chemistry that uses metalloid tin clusters as a start- ing material is of fundamental interest towards understand- ing the reactivity of such compounds. Since we identified {Sn10(Si(SiMe3)3)4} 2� 7 as an ideal candidate for such reactions, we present a further step in the understanding of metalloid tin cluster chemistry. In contrast to germanium chemistry, ligand elimination seems to be a major reaction channel, which leads to the more open metalloid cluster {Sn10(Si(SiMe3)3)3} � 9, in which the Sn core is only shielded by three Si(SiMe3)3 ligands. Compound 9 is obtained through different routes and is crystallised together with two differ- ent countercations. Besides the structural charact…
Coherent Electronic Coupling versus Localization in Individual Molecular Dimers
2004
International audience; The electronic excitation transfer and coherent electronic coupling strength were investigated in molecular dimers by spectrally resolved confocal fluorescence spectroscopy. The direct probe of electronic coupling strength distribution was possible due to static disorder in polymer host by single molecule measurements. The dimers with delocalized excitation were also found in comparison to emission originated from localized states. The delocalized and localized state transitions were observed for dimers which were attributed to structural fluctuations of guest-host system.
Dynamics of weak interactions in the ligand layer of meta-mercaptobenzoic acid protected gold nanoclusters Au68(m-MBA)32 and Au144(m-MBA)40
2020
Atomically precise metal nanoclusters, stabilized and functionalized by organic ligands, are emerging nanomaterials with potential applications in plasmonics, nano-electronics, bio-imaging, nanocatalysis, and as therapeutic agents or drug carriers in nanomedicine. The ligand layer has an important role in modifying the physico-chemical properties of the clusters and in defining the interactions between the clusters and the environment. While this role is well recognized from a great deal of experimental studies, there is very little theoretical information on dynamical processes within the layer itself. Here, we have performed extensive molecular dynamics simulations, with forces calculated…
Positron Annihilation in Alkali Halides at Low Temperatures
1986
We report on low-temperature positron studies for pure, single crystals of the alkali halides KCl, NaCl and NaF. Strong temperature dependences are observed in the lifetime and angular correlation measurements in the temperature range 10–300 K. Delocalized para-positronium is observed at low temperatures in the three crystals. The broadening, with rising temperature, of the narrow peak in the angular correlation curve can be accounted for by the self-trapping model of positronium. The results are discussed in the light of this model, in terms of positronium localization at imperfections and in terms of positron interactions with imperfections created in the spur of the positron. The increas…
Ionic iridium complex and conjugated polymer used to solution-process a bilayer white light-emitting diode.
2013
Bilayer white light-emitting devices are prepared from solution, using an ionic orange phosphorescent organometallic complex and a neutral fluorescent conjugated polymer. Because of the very different polarity of the two components, they dissolve in orthogonal solvents, allowing for the direct deposition of the blue emitter on top of the orange emitter without the need of cross-linking or special coating methodology. Fine tuning of the layer thickness of both light-emitting layers allows for the color tuning of different types of white light.
Facile laser-assisted synthesis of inorganic nanoparticles covered by a carbon shell with tunable luminescence
2015
We report a one-step strategy at ambient conditions for the production of hybrid inorganic core–carbon shell nanoparticles by means of pulsed laser ablation of inorganic targets (LiNbO3, Au, and Si) in hydrocarbon liquids such as toluene and chloroform. The core of these spherical nanoparticles consists of the target material, whereas the shells are carbon structures (multilayer graphite-type carbon and amorphous carbon), which are formed due to the thermal decomposition of the organic liquid in contact with hot inorganic nanoparticles ejected from the bulk target. These carbon shells emit photoluminescence in the blue-green spectral region and the obtained luminescence, in which the lumine…
Vibrational relaxation of matrix-isolated carboxylic acid dimers and monomers.
2009
Femtosecond mid-IR transient absorption spectroscopy was used to probe the vibrational dynamics of formic acid and acetic acid isolated in solid argon following excitation of the fundamental transition of the carbonyl stretching mode. Carboxylic acids form extremely stable H-bonded dimers, hindering the study of the monomeric species at equilibrium conditions. The low-temperature rare-gas matrix isolation technique allows for a unique control over aggregation enabling the study of the monomer vibrational dynamics, as well as the dynamics of two distinct dimer structures (cyclic and open chain). This study provides insight into the role of the methyl rotor and hydrogen bonding in the vibrati…
Molecular modeling studies of interactions between sodium polyacrylate polymer and calcite surface
2013
Abstract The interactions between calcite pigment and sodium polyacrylate dispersing agent, widely used in papermaking as paper coating components, were investigated using classical force field and quantum chemical approaches. The objective was to understand interactions between the calcite surface and sodium polyacrylate polymer at 300 K using molecular dynamics simulations. A quantum mechanical ab initio Hartree–Fock method was also used to obtain detailed information about the sodium polyacrylate polymer structure. The effect of water molecules (moisture) on the interactions was also examined. Calculations showed that molecular weight, branching and the orientation of sodium polyacrylate…
Investigating self-assembly and metal nanoclusters in aqueous di-block copolymers solutions
2002
Self-assembling properties of di-block copolymers/ surfactant hybrids in aqueous solution can be exploited to obtain metal nanoparticles stable dispersion. Results will be presented here for polystyrene-block-poly(ethylene oxide) solutions. A SANS structural investigation has been performed over different molecular weights of both hydrophilic and hydrophobic block, by varying temperature and concentration of the copolymer. A SAXS characterization of micellar systems containing Pt nanoparticles is reported.
ChemInform Abstract: Imidazolium and Pyridinium Salts - Solvents Influencing the Rate and Direction of the Fries, Beckmann, and Claisen Rearrangement…
2010
The effects of the structural elements of the ionic liquid media on the direction of these rearrangements and the product yields are studied.