Rhodium(I)/Zn(OTf)2‐Catalyzed Asymmetric Ring Opening/Cyclopropanation of Oxabenzonorbornadienes with Phosphorus Ylides

The strong binding ability of P‐ylides with transition metals limits the utilization of stabilized P‐ylide as nucleophiles in asymmetric organometallic catalysis. Herein we describe the first rhodium‐catalyzed asymmetric ring‐opening reaction of P‐ylides utilizing oxabicyclic alkenes as the electrophilic partner. Various P‐ylides including ester‐, ketone‐ and amide‐style P‐ylides are all applicable. This asymmetric reaction occurs through the cleavage of two bridgehead C?O bonds and the formation of two C?C bonds, and oxabenzonorbornadienes are used as 1,4‐biselectrophiles, thus providing access to benzonorcaradienes in good yields with high enantioselectivity and perfect diastereoselectivity. The present protocol also constitutes the first highly enantioselective direct catalytic asymmetric cyclopropanation of stabilized P‐ylide nucleophiles.     

Concise Synthesis of Open‐Cage Fullerenes for Oxygen Delivery

Open‐cage fullerenes with a 19‐membered orifice were prepared in three steps from C₆₀. The key step for cage‐opening is aniline mediated ring expansion of a fullerene‐mixed peroxide with a ketolactone moiety on the orifice. Release of ring strain on the spherical fullerene cage served as the main driving force for the efficient cage‐opening sequence. Encapsulation of oxygen could be achieved at room temperature under moderate pressure (50 atm) and the encapsulated oxygen could be released slowly under ambient conditions. The activation energy of the oxygen‐releasing process is 18.8 kcal mol^?1 and the half‐life at 37 °C was 73 min, which makes this open‐cage fullerene derivative a potential oxygen‐delivery material.     

Computational insight into excited states of the ring-opening radicals from the pyrolysis of furan biofuels

The low-lying valence excited states and Rydberg states of the radical species from the ring-opening reactions in pyrolysis of furan biofuels have been determined by extensive density functional theory and sophisticated wave function theory calculations. The radicals 1-C₄H₅O-2, 2-furylCH₂, and 4-C₆H₇O with the delocalized π-type single electron are predicted to be most stable among the reactive species here for furan, 2-methyfuran, and 2,5-dimethylfuran, respectively. Predicted vertical transition energies by TD-CAM-B3LYP show good agreement with those by CASPT2. Some among the electronic excitations to low-lying states can take place in the visible light region, and they may be involved in the combustion process. Further surface hopping dynamics simulations on the excited states of the most stable ring-opening radical 1-C₄H₅O-2 of furan as an example reveal that 89.9% sampling trajectories at the initial excited state of 2²A”(π¹π*²) decay to the 1²A’(n¹π*²) state within an average of 384 fs, and then 81.2% trajectories at the 1²A’ state go to the ground state within an average of 114 fs. At the end of the simulation for 1000 fs, 18.8% trajectories still stay on the excited states of 2²A” and 1²A’, suggesting that the reactive radicals in the ground state are mainly responsible for the combustion chemistry of furan biofuels. © 2018 Wiley Periodicals, Inc.     

Adamantane‐Substituted Acridine Donor for Blue Dual Fluorescence and Efficient Organic Light‐Emitting Diodes

To date, blue dual fluorescence emission (DFE) has not been realized because of the limited choice of chemical moieties and severe geometric deformation of the DFE emitters leading to strong intramolecular charge transfer (ICT) with a large Stokes shift in excited states. Herein, an emitter (1′r,5′R,7′S)‐10‐(4‐(4,6‐diphenyl‐1,3,5‐triazin‐2‐yl)phenyl)‐10H‐spiro [acridine‐9,2′‐adamantane] (a‐DMAc‐TRZ) containing a novel adamantane‐substituted acridine donor is reported, which exhibits unusual blue DFE. The introduction of the rigid and bulky adamantane moiety not only suppressed the geometry relaxation in excited state, but also induced the formation of quasi‐axial conformer (QAC) and quasi‐equatorial conformer (QEC) geometries, leading to deep‐blue conventional fluorescence and sky‐blue thermally activated delayed fluorescence (TADF). The resulting organic light‐emitting diodes (OLEDs) achieved a maximum external quantum efficiency (EQE) of about 29 %, which is the highest reported for OLEDs based on dual‐conformation emitters.     

Fluorometric Recognition of Nucleotides within a Water‐Soluble Tetrahedral Capsule

The design of aqueous probes and binders for complex, biologically relevant anions presents a key challenge in supramolecular chemistry. Herein, a tetrahedral assembly with cationic faces and corners is reported that is capable of discriminating between anionic and neutral guests in water. Electrostatic repulsion between subcomponents can be overcome by the addition of an anionic template, or generating a robust covalent framework by incorporating tris(2‐aminoethyl)amine (TREN). The resultant TREN‐capped, water‐soluble, fluorescent cage binds mono‐ and poly‐phosphoric esters, including nucleotides. Its covalent skeleton renders it stable at micromolar concentrations in water, enabling the fluorometric detection of biologically relevant guests in an aqueous environment. Selective supramolecular encapsulants, such as 1 , could enable new sensing applications, such as recognition of toxins and drugs, under biological conditions.     

Purity of MgH2 Improved by the Process of Pre-milling Assisted Hydriding of Mg Powder under a Hydrogen Pressure of 0.5 MPa

Russian Journal of Physical Chemistry A - Magnesium hydride (MgH2) is a very promising hydrogen storage material due to its high hydrogen storage capacity (7.6 wt %) and low cost. It has been paid...     

Tri‐Spiral Donor for High Efficiency and Versatile Blue Thermally Activated Delayed Fluorescence Materials

Blue thermally activated delayed fluorescence (TADF) emitters that can simultaneously achieve high efficiency in doped and nondoped organic light‐emitting diodes (OLEDs) are rarely reported. Reported here is a strategy using a tri‐spiral donor for such versatile blue TADF emitters. Impressively, by simply extending the nonconjugated fragment and molecular length, aggregation‐caused emission quenching (ACQ) can be greatly alleviated to achieve as high as a 90 % horizontal orientation dipole ratio and external quantum efficiencies (EQEs) of up to 33.3 % in doped and 20.0 % in nondoped sky‐blue TADF‐OLEDs. More fascinatingly, a high‐efficiency purely organic white OLED with an outstanding EQE of up to 22.8 % was also achieved by employing TspiroS‐TRZ as a blue emitter and an assistant host. This compound is the first blue TADF emitter that can simultaneously achieve high electroluminescence (EL) efficiency in doped, nondoped sky‐blue, and white TADF‐OLEDs.     

Signal enhancement of electrochemical DNA biosensors for the detection of trace heavy metals

Heavy-metal pollution has attracted intensive attention from the public because of the severe threats of heavy metals to the ecosystem and human health. Ultralow concentration of heavy metals in aquatic environment leads to the urgent needs of sensitive approaches for heavy-metal detection. Electrochemical DNA biosensors present outstanding superiority in convenience, selectivity, and sensitivity compared with conventional methods. To achieve the ultralow detection limit, efforts have been made to implement signal enhancement strategies to develop electrochemical DNA biosensors with enhanced sensing performance. This review focuses on the recent progress in signal enhancement strategies applied to electrochemical DNA biosensors for heavy-metal-ion detection including nicking enzyme–assisted amplification, the utilization of core–shell nanoparticles, and nanocomposites modification.     

密排纳米团簇薄膜应变传感器的响应特性及其与团簇覆盖率的相关性

本文通过在PET薄膜上的叉指电极间沉积Pd纳米团簇制备了柔性应变传感器件.传感器通过测量纳米团簇薄膜的电导随PET薄膜形变的变化而产生对应变的响应,不仅具有高的仪表因子,而且具有宽的量程.实验发现,由于密排纳米团簇阵列的电子输运具有渗流特征,造成应变传感器的响应特性与纳米团簇的覆盖率紧密相关.通过控制纳米团簇的沉积过程,制备了由覆盖率接近有效渗流阈值的纳米团簇点阵构成的应变传感器.从最低应变探测限到0.3%应变之间,传感器件具有线性响应且仪表因子高达55.在更高的应变时,仪表因子进一步达到200.纳米团簇薄膜甚至还可以对达到8%应变的巨大形变产生响应,对应的应变因子达到惊人的3500.     

Thermodynamic Nonequilibrium Features in Binary Diffusion

Diffusion is a ubiquitous physical phenomenon where thermodynamic nonequilibrium effects(TNEs) are outstanding issues. In this work, we employ the discrete Boltzmann method to investigate the TNEs in the dynamic process of binary diffusion. The main features of the distribution function in velocity space are recovered and discussed.It is found that, with the decreasing gradients of macroscopic quantities(such as density, concentration, velocity, etc.),both the local and global TNEs decrease with the time but increase with the relaxation time in a power law, respectively.