Formation of a Pillar[5]arene‐Based Two‐Dimensional Poly‐Pseudo‐Rotaxane: Threading and Crosslinking by the Same Guest Molecules

A one‐pot reaction of the A1/A2‐thiopyridyl pillar[5]arene L with silver(I) trifluoroacetate in the presence of the linear dinitrile guest C8 , [CN(CH₂)_nCN, n=8], afforded the first example of a two‐dimensional (2D) poly‐pseudo‐rotaxane {[(μ₄‐Ag)₂( C8 @ L )₂(μ ‐C8 )](CF₃CO₂)₂}_n. Surprisingly, in this structure the C8 guest not only threads into the pillar[5]arene unit but also crosslinks the 1D coordinative polymeric arrays. The formation of the 2D poly‐pseudo‐rotaxane is driven by an adaptive rearrangement of the components that minimizes the steric clashes not only between the threaded guests but also between the threaded and crosslinked guests where crosslinking occurs. A pathway for the formation of the 2D poly‐pseudo‐rotaxane is proposed.     

Photoelectrochemical CO2 Reduction with a Rhenium Organometallic Redox Mediator at Semiconductor/Aqueous Liquid Junction Interfaces

Electrochemical and photoelectrochemical CO₂ reductions were carried out with Re(bh‐bipy)(CO)₃(OH₂) cocatalysts in aqueous electrolytes. Competition between hydrogen evolution and CO₂ reduction was observed under (photo)electrochemical conditions for both glassy carbon and CuInS₂ electrodes. The partial current density for CO generation is limited even though the additional potential is applied. However, electrochemical hydrogen evolution was suppressed under photoelectrochemical conditions, and the selectivity and partial current density for CO were considerably increased when compared to the electrochemical reduction in an identical electrode/electrolyte system. This finding may provide insights into using semiconductor/liquid junctions for solar fuel devices to overcome the limitations of electrolysis systems with an external bias.     

Effect of ethanolamine passivation of ZnO nanoparticles in quantum dot light emitting diode structure

The aging of ZnO nanoparticles in quantum dot light-emitting diode (QD-LED) structures was studied. Coarsening of as-synthesized ZnO nanoparticles is observed in both solution and thin film structures, which potentially deteriorates the performance of QD-LED devices over time. First, the temperature effect on ZnO coarsening was investigated, and it was revealed that aging of ZnO nanoparticles is faster at higher temperature due to a diffusion-controlled mechanism of nanoparticle coarsening. To observe aggregation of ZnO in the film state, the electron transporting part (ZnO/Al) of the QD-LED structure was prepared. The current density of a ZnO film and an electron-only device (QD/ZnO between two electrodes) was also measured. Resistance of the film increased as a function of aging time, which corresponded with observations of the ZnO film by optical microscopy. Aggregation of ZnO nanoparticles was directly measured by the root-mean-square value using atomic force microscopy. Ethanolamine (EA) stabilizer was added to the ZnO solution to disperse the ZnO nanoparticles without aggregation. The effect of EA on the surface passivation of the ZnO found to suppress pinhole formation, as revealed by scanning electron microscopy observations. Finally, the device lifetime was measured for QD-LEDs with EA-stabilized ZnO to understand the effect of ZnO aging on long-term QD-LED device operation.     

Atomic and Magnetic Long-Range Orderings in BaLaMRuO6 (M=Mg and Zn)

The crystal structures of double perovskite BaLaMRuO₆ (M=Mg, Zn) obtained from the refinements on both X-ray and neutron diffraction data, different from those reported previously that used either X-ray or neutron diffraction data alone, are reported. The room temperature X-ray and neutron data were refined with a model in the tetragonal space group I4/m (a=5.6230(4), c=7.964(1) Å, V=251.81(4) ų for M=Mg; a=5.6521(3), c=7.9987(9) Å, V=255.53(3) ų for M=Zn). The low-temperature neutron diffraction data of the two compounds are also refined in the same space group (a=5.6156(4), c=7.953(1) Å, V=250.80(4) ų for M=Mg at 13 K; a=5.6418(4), c=7.981(1) Å, V=254.03(4) ų for M=Zn at 10 K). Both compounds show almost complete ordering of B-site atoms (M/Ru). For both compounds, the low-temperature neutron diffraction data below about 20 K showed magnetic diffraction peaks that could be accounted for with a Type I antiferromagnetic ordering of Ru spins in an atomically ordered double perovskite structure. These compounds showed discrepancies between field cooled and zero field cooled magnetization data below the antiferromagnetic ordering temperatures.     

The effect of nonlinearity on unstable zones of Mathieu equation

Mathieu equation is a well-known ordinary differential equation in which the excitation term appears as the non-constant coefficient. The mathematical modelling of many dynamic systems leads to Mathieu equation. The determination of the locus of unstable zone is important for the control of dynamic systems. In this paper, the stable and unstable regions of Mathieu equation are determined for three cases of linear and nonlinear equations using the homotopy perturbation method. The effect of nonlinearity is examined in the unstable zone. The results show that the transition curves of linear Mathieu equation depend on the frequency of the excitation term. However, for nonlinear equations, the curves depend also on initial conditions. In addition, increasing the amplitude of response leads to an increase in the unstable zone.     

Ab initio investigations of the C2F4S isomers and of their interconversions

The transition states and the activation energies for the unobserved isomerization reactions between the three possible C₂F₄S isomers with divalent sulfur, trifluorothioacetyl fluoride 1, tetrafluorothiirane 2, and trifluoroethenesulfenyl fluoride 3, have been determined by ab initio Hartree-Fock (HF), Møller-Plesset second-order perturbation (MP2) calculations and by Gaussian-3 theory. The results show that the unobserved isomerization reactions are feasible. Furthermore, all three isomers should exist as stable species, but the unknown isomer, 3, is considerably less stable than the known isomers, 1 and 2.