Reactivity,Regioselectivity,and Synthetic Application of 2-Pyrenyl Units in Scholl Reactions

We herein report the reactivity and regioselectivity of 2-pyrenyl as a coupling unit in Scholl reactions.On the basis of the Scholl reactions of hexaarylbenzene substrates,we have found that pyrenyl units are preferably oxidized over naphthyl and phenyl units under appropriate Scholl reaction conditions,allowing divergent synthesis through a highly controllable intramolecular coupling sequence.We find that the C1 and C3 positions of the 2-pyrenyl unit are the favorable sites for intramolecular coupling while C4 is not reactive to allow further coupling.The reactivity and regioselectivity pattern can be explained by the spin density distribution,which shows that carbon-carbon bonds preferably form at sites with higher positive spin density.Guided by these findings,we successfully synthesized a double helicene and a sextuple helicene through the controlled Scholl reactions of 2-pyrenyl units.

Structural, optical, and electrical properties of phase- controlled cesium lead iodide nanowires

Cesium lead iodide （CsPbIa）, in its black perovskite phase, has a suitable bandgap and high quantum efficiency for photovoltaic applications. However, CsPbI3 tends to crystalize into a yellow non-perovskite phase, which has poor optoelectronic properties, at room temperature. Therefore, controlling the phase transition in CsPbI3 is critical for practical application of this material. Here we report a systematic study of the phase transition of one-dimensional CsPbI3 nanowires and their corresponding structural, optical, and electrical properties. We show the formation of perovskite black phase CsPbIa nanowires from the non-perovskite yellow phase through rapid thermal quenching. Post-transformed black phase CsPbI3 nanowires exhibit increased photoluminescence emission intensity with a shrinking of the bandgap from 2.78 to 1.76 eV. The perovskite nanowires were photoconductive and showed a fast photoresponse and excellent stability at room temperature. These promising optical and electrical properties make the perovskite CsPbI3 nanowires attractive for a variety of nanoscale optoelectronic devices.

Morphology-controlled transformation of Cu@Au core-shell nanowires into thermally stable Cu3Au intermetallic nanowires

Multimetallic nanowires with long-range atomic ordering hold the promise of unique physicochemical properties in many applications.Here we demonstrate the synthesis and study the stability of CU3AU intermetallic nanowires.The synthesis is achieved by using Cu@Au core-shell nanowires as precursors.With appropriate Cu/Au stoichiometry,the Cu@Au core-shell nanowires are transformed into fully ordered Cu3Au nanowires under thermal annealing.Thermally-driven atom diffusion accounts for this transformation as revealed by X-ray diffraction and electron microscopy studies.The twin boundaries abundant in the Cu@Au core-shell nanowires facilitate the ordering process.The resulting CU3AU intermetallic nanowires have uniform and accurate atomic positioning in the crystal lattice,which enhances the nobility of Cu.No obvious copper oxides are observed in fully ordered Cu3Au nanowires after annealing in air at 200℃,a temperature that is much higher than those observed in Cu@Au core-shell and pure Cu nanowires.This work opens up an opportunity for further research into the development and applications of intermetallic nanowires.

Lead halide perovskite nanowires stabilized by block copolymers for Langmuir-Blodgett assembly

The rapid development of solar cells based on lead halide perovskites(LHPs)has prompted very active research activities in other closely-related fields.Colloidal nanostructures of such materials display superior optoelectronic properties.Especially,onedimensional(1D)LHPs nanowires show anisotropic optical properties when they are highly oriented.However,the ionic nature makes them very sensitive to external environment,limiting their large scale practical applications.Here,we introduce an amphiphilic block copolymer,polystyrene-block-poly(4-vinylpyridine)(PS-P4VP),to chemically modify the surface of colloidal CsPbBr3 nanowires.The resulting core-shell nanowires show enhanced photoluminescent emission and good colloidal stability against water.Taking advantage of the stability enhancement,we further applied a modified Langmuir-Blodgett technique to assemble monolayers of highly aligned nanowires,and studied their anisotropic optical properties.

Spontaneous twisting of a collapsed carbon nanotube

我们学习崩溃并且碳 nanotube 的随后的自发的扭动由在 situ 传播电子显微镜学(TEM ) 。习俗大小的 nanotube 被有选择地从一个父母提取壳首先在显微镜创造多围的试管。围很少的、大直径的女儿 nanotube 被驱使经由机械刺激，如带的折叠试管自发地沿着它的长轴在以后扭动崩溃。在 situ 衍射，实验充分描绘 uncollapsed 和折叠试管。试验性的观察和联系理论分析显示扭动的起源是压缩紧张。

Sulfur-doped graphene anchoring of ultrafine Au25 nanoclusters for electrocatalysis

The biggest challenge of exploring the catalytic properties of under-coordinated nanoclusters is the issue of stability.We demonstrate herein that chemical dopants on sulfur-doped graphene(S-G)can be utilized to stabilize ultrafine(sub-2 nm)Au_(25)(PET)18 clusters to enable stable nitrogen reduction reaction(NRR)without significant structural degradation.The Au_(25)@S-G exhibits an ammonia yield rate of 27.5μgNH_(3)·mgAu^(-1)·h^(-1)at-0.5 V with faradic efficiency of 2.3%.More importantly,the anchored clusters preserve~80%NRR activity after four days of continuous operation,a significant improvement over the 15%remaining ammonia production rate for clusters loaded on undoped graphene tested under the same conditions.Isotope labeling experiments confirmed the ammonia was a direct reaction product of N2 feeding gas instead of other chemical contaminations.Ex-situ X-ray photoelectron spectroscopy and X-ray absorption near-edge spectroscopy of post-reaction catalysts reveal that the sulfur dopant plays a critical role in stabilizing the chemical state and coordination environment of Au atoms in clusters.Further ReaxFF molecular dynamics(RMD)simulation confirmed the strong interaction between Au nanoclusters(NCs)and S-G.This substrate-anchoring process could serve as an effective strategy to study ultrafine nanoclusters’electrocatalytic behavior while minimizing the destruction of the under-coordinated surface motif under harsh electrochemical reaction conditions.

Real time imaging of two-dimensional iron oxide spherulite nanostructure formation

The formation of complex hierarchical nanostructures has attracted a lot of attention from both the fundamental science and potential applications point of view.Spherulite structures with radial fibrillar branches have been found in various solids;however,their growth mechanisms remain poorly understood.Here,we report real time imaging of the formation of two-dimensional(2D)iron oxide spherulite nanostructures in a liquid cell using transmission electron microscopy(TEM).By tracking the growth trajectories,we show the characteristics of the reaction front and growth kinetics.Our observations reveal that the tip of a growing branch splits as the width exceeds certain sizes(5.5–8.5 nm).The radius of a spherulite nanostructure increases linearly with time at the early stage,transitioning to nonlinear growth at the later stage.Furthermore,a thin layer of solid is accumulated at the tip and nanoparticles from secondary nucleation also appear at the growing front which later develop into fibrillar branches.The spherulite nanostructure is polycrystalline with the co-existence of ferrihydrite and Fe3O4 through-out the growth.A growth model is further established,which provides rational explanations on the linear growth at the early stage and the nonlinearity at the later stage of growth.

Cooperative effects at the interface of nanocrystalline metal-organic frameworks

Controlling the chemistry at the interface of nanocrystalline solids has been a challenge and an important goal to realize desired properties. Integrating two different types of materials has the potential to yield new functions resulting from cooperative effects between the two constituents. Metal-organic frameworks （MOFs） are unique in that they are constructed by linking inorganic units with organic linkers where the building units can be varied nearly at will. This flexibility has made MOFs ideal materials for the design of functional entities at interfaces and hence allowing control of properties. This review highlights the strategies employed to access synergistic functionality at the interface of nanocrystalline MOFs （nMOFs） and inorganic nanocrystals （NCs）.