Latest ArticlesA rhodium-catalyzed directing group promoted selective C–H olefination reaction of indolizines at the 8-position is reported. Di-olefination at 2,8-positions also achieved with silver hexafluoroantimonate as an additive under similar reaction conditions. Weakly coordinating groups, such as ketone, aldehyde, amide and ester, were used as directing groups. The ester group can be removed under acid conditions and therefore is used as a traceless directing group.
An eco-friendly, sustainable and practical method for the efficient preparation of 5-organylselanyl uracils through the electrochemical selenylation of uracils and diorganyl diselenides at room temperature under oxidant- and external electrolyte-free conditions was developed.
The effects of concentration and an oriented external electric field on the transformations of hydrogenbonded structures of trimesic acid (TMA) and terephthalic acid (TPA) have been investigated at a liquid–solid interface by scanning tunneling microscopy (STM). The triangular periodic TMA framework can be transformed into a flower-like structure by changing the STM sample bias sign in situ. Networks of TMA and TPA are porous at a negative substrate bias, but typically change to relatively compact forms when the polarity of the applied bias is reversed. This change is reversible if the applied bias is reversed. The effects have potentials to locally control the capture and release of analytes in host-guest systems and the 2D morphology in multicomponent layers.
Two types of palladium(Ⅱ)-based metallacalixarenes [ML]2+ and [ML2]2+ have been synthesized through coordination-driven self-assembly from a series of flexible pyridine-bridged diimidazole ligands [2,6-bis ((1H-imidazol-1-yl)methyl) pyridine (L1), 2,6-bis((1H-benzo[d]imidazol-1-yl)methyl)pyridine (L2), 2,6-bis((1H-naphtho[2,3-d]imidazol-1-yl)methyl)pyridine (L3)], with palladium(Ⅱ)-based building blocks [Pd(BF4)2(M1-BF4) and (tmeda)Pd(NO3)2 (M2-NO3) (tmeda = N, N, N', N'-tetramethyl-ethylenediamine)]. All complexes were characterized by NMR spectroscopy (1H NMR and 13C NMR), mass spectrometry (CSI-MS, ESI-HRMS) and elemental analysis. The single crystal X-ray diffraction analysis of [M1L22](NO3)2, [M1L23](NO3)2, [M1L23](PF6)2 and [M2L3](NO3)2 further confirmed the uniquely single bowl-shape and double bowl-shape structures. The anion binding properties within the metallacalixarenes as receptors were also investigated by NMR titration experiments in DMSO.
Inorganic lead halide perovskites are attractive optoelectronic materials owing to their relative stability compared to organic cation alternatives. The chemical vapor deposition (CVD) method offers potential for high quality perovskite film growth. The deposition temperature is a critical parameter determining the film quality owing to the melting difference between the precursors. Here, perovskite films were deposited by the CVD method at various temperatures between 500-800 ℃. The perovskite phase converts from CsPb2Br5 to CsPbBr3 gradually as the deposition temperature is increased. The grain size of the perovskite films also increases with temperature. The phase transition mechanism was clarified. The photoexcited state dynamics were investigated by spatially and temporally resolved fluorescence measurements. The perovskite film deposited under 750 ℃ condition is of the CsPbBr3 phase, showing low trap-state density and large crystalline grain size. A photodetector based on perovskite films shows high photocurrent and an on/off ratio of ~2.5×104.
Smart materials, such as stimuli-responsive luminescence, have attracted much attentions due to their potential application in semiconductorfiled. In this context, platinumcomplexes of (dfppy-DC)Pt(acac) and (dfppy-O-DC)Pt(acac) were prepared and characterized, in which (2-(4', 6'-difluorophenyl)pyridinato-N, C2')(2,4-pentanedionato-O, O)Pt(Ⅱ) was used as the planar emission core and 9-(4-(phenylsulfonyl) phenyl)-9H-carbazole (DC) was regard as the bent pendent. Both platinum complexes showed bright emission in solution and solid state, concomitant with charming external-stimuli-responsive emission under mechanical grinding, organic solvent vapors and pressure. The change emission color spanned from yellow to near-infrared region. Using the platinum complexes as the dopant, solution processable organic light-emitting diodes (OLEDs) were fabricated and a maximum external quantum efficiency of ~18% was achieved, which is the highest value among the reported solution-processable OLEDs based on external-stimuli-responsive luminescence.This research demonstrated that platinum complex can show promising stimuli responsive emission via ingenious molecular design, indicating a novel way for developing the smart materials in semiconductor filed.
Metal organic frameworks (MOFs) are a kind of promising materials in many applications, while the fast and controllable synthesis of MOFs is still challenging. Here, taking HKUST-1 as illustration, a micro-plasma electrochemistry (MIPEC) strategy was developed to accelerate the synthesis process of MOFs with micro-plasma acting as cathode. Treating the HKUST-1 precursor solution with micro-plasma cathode could not only transfer the electrons into the solution leading to the deprotonation effect, but also generate radical species to trigger and accelerate the nucleation and growth of MOFs at the plasma-liquid interface. Thus, uniform and nanosize MOFs could be prepared within minutes. The obtained MOFs show similar excellent uranium adsorption properties compared with those obtained by other method, with a highly adsorption capability of uranium with 550 mg/g in minutes. The novel MIPEC strategy developed in this work provides an alternative for controllable synthesis of MOFs, and especially has potential application in accelerating traditional organic synthesis.
Graphene nanosheets are widely used in anti-corrosion polymeric coating as filler, owing to the excellent electrochemical inertness and barrier property. However, as the arrangement of graphene nanosheets is difficult to form a perfect layered structure, polymeric coating with graphene nanosheets usually needs micron-scale thickness to ensure the enhancement of corrosion protection. In this work, layer-by-layer stacked graphene nanocoatings were fabricated on stainless steel by self-assembly based on Marangoni effect. The anti-corrosion property of graphene coatings were studied through Tafel polarization curves, electrochemical impedance spectroscopy and accelerated corrosion test with extra applied voltage. The self corrosion current density of optimized three-layered graphene coated sample was one quarter of that of bare stainless steel. And the self corrosion potential of optimized sample is increased to -0.045 V. According to the results, graphene nanocoatings composed of layered nanosheets exhibits good anti-corrosion property. Besides, the self-assembly method provide a promising approach to make layered-structure coating for other researches about 2D material nanosheets.
Metal-nitrogen-carbon materials (M-N-C) are non-noble-metal-based alternatives to platinum-based catalysts and have attracted tremendous attention due to their low-cost, high abundance, and efficient catalytic performance towards the oxygen reduction reaction (ORR). Among them, Fe-based materials show remarkable ORR activity, but they are limited by low selectivity and low stability. To address these issues, herein, we have synthesized FeCu-based M-N-C catalysts, inspired by the bimetal center of cytochrome c oxidase (CcO). In acidic media, the selectivity was notably improved compared with Fe-based materials, with peroxide yields less than 1.2% (< 1/3 of the hydrogen peroxide yields of Fe-N-C catalysts). In addition to Cu-N-C catalysts which can catalytically reduce hydrogen peroxide, the reduction current of hydrogen peroxide using FeCu-N-C-20 exceeded that of Fe-N-C by about 6% when the potential was greater than 0.4 V. Furthermore, FeCu-based M-N-C catalysts suffered from only a 15 mV attenuation in their half-wave potentials after 10, 000 cycles of accelerated degradation tests (ADT), while there was a 30 mV negative shift for Fe-N-C. Therefore, we propose that the H2O2 released from Fe-Nx sites or N-doped carbon sites would be reduced by adjacent Cu-Nx sites, resulting in low H2O2 yields and high stability.
Transition metal phosphide (TMP) based electrocatalysts possessing special crystal and electronic structures attract broad attention in the field of electrocatalysis. Immense effort is made to optimize TMP catalysts aiming to satisfy the electrochemical catalysis performance. In this work, an environmentally friendly in situ green phosphating strategy and spatial limiting effect of the RuCo precursor is employed to fabricate the ruthenium nanoclusters anchored on cobalt phosphide hollow microspheres (Ru NCs/Co2P HMs). The obtained Ru NCs/Co2P HMs electrocatalysts exhibit high hydrogen evolution reaction (HER) activity at wide pH ranges, which require an overpotential of 77 mV to achieve the current density of 10 mA/cm2 in 0.5 mol/L H2SO4 and 118 mV in 1.0 mol/L KOH. Besides, the multifunctional Ru NCs/Co2P HMs exhibit good oxygen evolution reaction (OER) activity with an overpotential of 197 mV to reach the current density of 10 mA/cm2 in 0.5 mol/L H2SO4, which is below that of the commercial RuO2 electrocatalyst (248 mV). A two-electrode electrolyzer is assembled as well, in acid electrolyte, it achieves a current density of 10 mA/cm2 at a voltage of 1.53 V, which is superior to that of the benchmark of precious metal-based electrolyzer (1.58 V).
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