Mechanochromism of Ag(I) complexes with iPrNHC(S)NHP(S)(OiPr)2

Reaction of the potassium salt of iPrNHC(S)NHP(S)(OiPr)(2) (HL) with AgPF(6) leads to the hexanuclear [{Ag(3)(iPrNHC(S)NP(S)(OiPr)(2)-S,S')(3)}(2)] ([(Ag(3)L(3))(2)]) complex. The reversible conversion between yellow-emitting ([(Ag(3)L(3))(2)]) and blue-emitting ([Ag(3)L(3)]) materials on grinding and recrystallization was established. [Ag(3)L(3)] was also prepared by a mechanically induced solid-state reaction.     

Highly efficient [Ni{iPrHNC(S)NP(S)(OiPr)2-1,3-N,S'}2]/PR3 (R3 = Me3, Me2Ph) complexes for the generation of Ni(0) for catalysis

We have developed new complexes of the type [Ni{iPrHNC(S)NP(S)(OiPr)(2)-1,3-N,S'}(2)]/PR(3) (R(3) = Me(3), Me(2)Ph) for the generation of Ni(0) catalysts which can be used for the catalytic addition of Ph(2)S(2) to 1-, 2- and 3-hexynes. A detailed study of the catalytic reaction mechanism suggests two possible pathways for the in situ formation of Ni(0) species, depending on the presence or absence of water.     

Conjugated circuits currents in hexabenzocoronene and its derivatives formed by joining proximal carbons

We report on calculated CC bond currents for a dozen derivatives of hexabenzocoroenene in which one or more proximal carbon atoms at the molecular periphery have been bridged. The approach that we use is graph‐theoretical in nature, following our outline of this method in 2003, which is based on finding all conjugated circuits in all Kekulé valence structures of these molecules. To the π‐electrons having 4n + 2 π‐electrons are assigned anticlockwise π‐electron currents and to conjugated circuits having 4n π‐electrons are assigned π‐electron currents. One may summarize the results reported in this work by stating that CC bond currents in the compounds considered decrease on going from peripheral rings to the central ring of the molecule, and also that CC bond currents decrease by insertion of bridges to proximal peripheral benzenoid rings. © 2012 Wiley Periodicals, Inc.     

Localized emitting state and energy transfer properties of quadrupolar chromophores and (multi)branched derivatives

In order to better understand the nature of intramolecular charge and energy transfer in multibranched molecules, we have synthesized and studied the photophysical properties of a monomer quadrupolar chromophore with donor-acceptor-donor (D-A-D) electronic push-pull structure, together with its V-shaped dimer and star-shaped trimers. The comparison of steady-state absorption spectra and fluorescence excitation anisotropy spectra of these chromophores show evidence of weak interaction (such as charge and energy transfer) among the branches. Moreover, similar fluorescence and solvation behavior of monomer and branched chromophores (dimer and trimer) implies that the interaction among the branches is not strong enough to make a significant distinction between these molecules, due to the weak interaction and intrinsic structural disorder in branched molecules. Furthermore, the interaction between the branches can be enhanced by inserting π bridge spacers (-C═C- or -C≡C-) between the core donor and the acceptor. This improvement leads to a remarkable enhancement of two-photon cross-sections, indicating that the interbranch interaction results in the amplification of transition dipole moments between ground states and excited states. The interpretations of the observed photophysical properties are further supported by theoretical investigation, which reveal that the changes of the transition dipole moments of the branched quadrupolar chromophores play a critical role in observed the two-photon absorption (2PA) cross-section for an intramolecular charge transfer (ICT) state interaction in the multibranched quadrupolar chromophores.     

Influence of the coordination mode in [Ni{RC(S)NP(S)(OiPr)2}2] for the formation of nickel-containing nanoparticles

The complex [Ni{2-PyNHC(S)NP(S)(OiPr)(2)-1,5,7-N,N',S}(2)] ([NiL(I)(2)]) dissolved in tri-n-octylphosphine (TOP) is decomposed in hot hexadecylamine (HDA) to give TOP-capped Ni nanoparticles. The same procedure using [Ni{2-MeC(6)H(4)NHC(S)NP(S)(OiPr)(2)}(2)-1,3-N,S] ([NiL(II)(2)]) and [Ni{PhC(S)NP(S)(OiPr)(2)-1,5-S,S'}(2)] ([NiL(III)(2)]) leads to the formation of NiS nanoparticles with the rhombohedral and hexagonal structures, respectively. NiH(x) nanoparticles were also produced from a mixture of [NiL(I)(2)] and N(2)H(4). The obtained Ni nanoparticles can be used for the catalytic addition of Ph(2)S(2) to 1-, 2- and 3-hexynes.     

Precipitation and characterization of hollow calcite nanoparticles

A method for preparation of significant amount of hollow rhombohedral calcite nanoparticles, based on carbonation of calcium hydroxide suspension, is described. The mineralogical and morphological analyses of the precipitate confirmed the existence of exclusively stable polymorphic modification, calcite, with the mean particle size of about 100 nm and the diameter of the holes observed at the surfaces that are about 50 nm. The analysis of carbonation kinetics pointed out to a complex mechanism of hollow particles formation at high initial supersaturation, that assumed nucleation of amorphous precursor calcium carbonate phase and its solution mediated transformation into nanosized crystalline calcite. The holes obtained at the calcite surfaces are most probably the imprints remained after the dissolution of amorphous calcium carbonate particles.     

Numerical investigation of plate edge and slot size effects in low yield stress measurements with a slotted plate device

There is a need for accurate yield stress measurements, especially in the case of low yield stress complex materials such as biological samples. This task cannot be accomplished with conventional rotational rheometers due to significant wall slip effects and the necessity to operate the device at very low shear rates, often beyond the limit that such rheometers can achieve. In this paper, we focused on the slotted plate method proposed recently for low yield stress measurements. Using computational fluid dynamics, we studied the effects of plate geometry on the measurement accuracy of the slotted plate method. Results of this study indicate that both wall slip effects and pressure drag force can be substantially reduced by adopting a thin plate with sharp front and rear edges, high slot area ratio, and large number of slots. If the plate has 30° triangular edges, a slot area ratio of 80%, and 12 slots, the slotted plate method overpredicts the yield stress of a 0.09 wt.% Carbopol dispersion (yield stress of 9.17 Pa) by only 8.4% under no-slip conditions and underpredicts the yield stress by 12.3% under free-slip conditions. Similar results were obtained for human saliva characterized by a very low yield stress (0.073 Pa).     

Soft photon problem in leptonic B-decays

We point out at the peculiarity of B→μν_μ decay, namely the enhancement of the soft photon events which originate from the structure dependent part of the B→μν_μγ amplitude. This may be a dominant source of systematic uncertainty and compromise the projected experimental uncertainty on Γ(B→μν_μ). We show that the effect of these soft photons can be controlled if the experimental cut on identification of soft photons is lowered and especially if the better resolution in identifying the momentum of muon emerging from B→μν_μ is made. A lattice QCD computation of the relevant form factors would be highly helpful for a better numerical control over the structure dependent soft photon emission.     

On functionalized fullerenes C 60 X n

Optimal configurations of functionalized fullerenes C ₆₀ X _n for n = 2, 4, 6, 8 have been determined by application of three topological stability measures. It has been found that the optimal configurations with higher n contain optimal configurations with lower values of n. Two stability measures prefer configurations in which functional groups Xs are crowded while the third one points to configurations with isolated pairs of Xs.