Electrical switching effect in a photochromic molecule between two graphene electrodes

We propose a single-molecule electrical switches consisting of a photochromic dimethyldihydropyrene/cyclophanediene molecule sandwiched between two graphene electrodes and investigate the electronic transport by using density-functional theory and nonequilibrium Green's function methods. The “open” and “closed” isomers of the photochromic molecule are shown to have electrical switching behavior and negative differential resistance effect. Moreover, it is also found that the switching ratio between two different conductive states depends on the ambient temperature, and the device behaves as a stable electrical switch around room temperature, which is in agreement with a recent experimental study of another photochromic molecule diarylethene reported by Jia et al. (2016) [17].     

M2B7-(M=Mg,Zn)团簇的双重芳香性促进Mg-Mg和Zn-Zn单键的形成

本文使用密度泛函理论设计了两个无需配体的具有Mg-Mg和Zn-Zn单键的团簇Mg₂B₇^-和Zn₂B₇^-. 这两种团簇的全局能量最低构型均以M₂²⁺(B₇^3-)的形式存在，其中M-M单键处于准平面六边形形状的B₇部分的上方. 化学键分析证实了这些团簇中Mg-Mg和Zn-Zn单键的存在，这些单键是在异常稳定的B₇^3-的驱动下生成的. 该B₇^3-部分同时具有σ和π双重芳香性. 计算得到Mg₂B₇^-和Zn₂B₇^-的垂直跃迁能分别为2.79 eV和2.94 eV.     

Reply to the Comment on “Realization of Lewis Basic Sodium Anion in the NaBH3− Cluster”

We reply to the comment by S. Pan and G. Frenking who challenged our interpretation of the Na^?:→BH₃ dative bond in the recently synthesized NaBH₃^? cluster. Our conclusion remains the same as that in our original paper ( https://doi.org/10.1002/anie.201907089 and https://doi.org/10.1002/ange.201907089 ). This conclusion is additionally supported by the energetic pathways and NBO charges calculated at UCCSD and CASMP2(4,4) levels of theory. We also discussed the suitability of the Laplacian of electron density (QTAIM) and Adaptive Natural Density Partitioning (AdNDP) method for bond type assignment. It seems that AdNDP yields more sensible results. This discussion reveals that the complex realm of bonding is full of semantic inconsistencies, and we invite experimentalists and theoreticians to elaborate this topic and find solutions incorporating different views on the dative bond.     

Effects of hydroxyl groups and hydrogen passivation on the structure,electrical and optical properties of silicon carbide nanowires

The effects of hydrogen and hydroxyl passivation on the structure, electrical and optical properties of SiCNWs were investigated. The passivation performance of different atoms (groups) were discussed by analyzing the distribution of electronic states and the polarity of chemical bonds. The results show that passivation can improve the stability of SiCNWs structure, and the effect of hydroxyl is better than hydrogen passivation. And hydrogen and hydroxyl passivation both increase the band gap of SiCNWs, and the changing trend of band gap is relevant to the polarity of the covalent bond formed by the passivation of surface atoms. Moreover, passivation enhances the stability of the optical properties of SiCNWs, resulting in narrowing of light absorption, photoconductivity and other spectra, and the response peak shifts to the deep ultraviolet region, which means that hydrogen or hydroxyl passivation of SiCNWs is likely to be a candidate material for deep ultraviolet micro-nano optoelectronic devices.     

纤维复合材料界面横向拉伸分析

以单纤维十字型横向拉伸试验为研究对象,对纤维/基体界面采用弹性-软化双线性内聚力模型,建立了纤维复合材料在横向拉伸作用下界面法向失效过程的解析模型。得到了沿纤维/基体圆周界面的法向应力分布,纤维/基体界面的状态与界面承载力和单纤维复合材料承载力的关系,以及内聚力参数和试件几何尺寸对它们的影响。结果表明:纤维/基体圆周界面在脱粘前经历全部弹性及弹性+软化两种状态;当界面为弹性状态时,界面法向应力随界面强度线性增加;当界面为弹性+软化状态时,界面软化范围随界面裂纹萌生位移的增加而增大;界面初始脱粘位置与拉伸荷载方向重合;界面初始脱粘时的界面承载力随界面强度及界面裂纹萌生位移的增加而增加,随界面裂纹生成位移的增加而降低;单纤维复合材料的脱粘荷载受基体截面尺寸的影响,当纤维体积含量相同时,沿荷载方向截面尺寸的增大对提高脱粘荷载更显著。     

Direct Transformation of Arenols Based on C—O Activation

In the view of substrate availability, atomic efficiency and cost, directly using arenols as coupling partners in cross‐coupling, would be one of the most attractive goals. Up to date, many efforts have been made to activate the C—O bond of phenols with different strategies, for example, through in‐situ formed intermediates, through a catalytic reductive dearomatization‐condensation‐rearomatization sequence or catalytic deoxygenation. In this review, we summarized recent advances in cross‐couplings of arenols as the electrophiles via C—O activation.     

Halogen bond between hypervalent halogens YF3/YF5 (Y=Cl,Br, I) and H2X (X= O,S, Se)

ABSTRACT

The complexes of H₂X (X?=?O, S, Se) with hypervalent halogens YF₃ and YF₅ (Y?=?Cl, Br, I) have been studied. The σ-hole on the Y atom participates in a halogen bond with the lone pair on the chalcogen atom. In addition, some secondary interactions coexist with the halogen bond in most complexes. The interaction energy correlates with the nature of both X and Y atoms. In most cases, the complex is more stable for the heavier Y atom and the lighter X atom. Of course, there are some exceptions in H₂X···YF₃. YF₃ forms a more stable complex with H₂X than does YF₅. These complexes are dominated by electrostatic interaction and the halogen bond involving H₂S and H₂Se exhibits some covalent character.

Halogen bond plays an important role in chemical reactions and multivalent halogens can regulate chemical reactions by participating in a halogen bond. Thus we compare the effect of the chalcogen electron donor on the strength and nature of halogen bonding involving multivalent halogens.     

Crystalline Divinyldiarsenes and Cleavage of the As=As Bond

The first divinyldiarsenes [{(NHC)C(Ph)}As]₂ (NHC=IPr 3 a , SIPr 3 b ; IPr=C{(NAr)CH}₂; SIPr=C{(NAr)CH₂}₂; Ar=2,6-iPr₂C₆H₃) are reported. Compounds 3 a and 3 b were prepared by the reduction of corresponding chlorides {(NHC)C(Ph)}AsCl₂ (NHC=IPr 2 a , SIPr 2 b ) with Mg. Calculations revealed a small HOMO–LUMO energy gap of 3.86 ( 3 a ) and 4.24 eV ( 3 b ). Treatment of 3 a with (Me₂S)AuCl led to the cleavage of the As=As bond to restore 2 a , which is expected to proceed via the diarsane [{(IPr)C(Ph)}AsCl]₂ ( 4 ). Remarkably, 4 as well as 2 a can be selectively accessed on treatment of 3 a with an appropriate amount of C₂Cl₆. Moreover, 3 a readily reacts with PhEEPh (E=Se or Te) at room temperature to give {(IPr)C(Ph)}As(EPh)₂ (E=Se 5 a ; Te 5 b ), revealing the cleavage of As=As and E−E bonds and the formation of As−E bonds. Such highly selective stepwise oxidation ( 3 a → 4 → 2 a ) and bond metathesis ( 3 a → 5 a , b ) reactions are unprecedented in main-group chemistry.     

含酰胺结构超低膨胀聚酰亚胺薄膜的热膨胀行为

采用联苯二酐与3种含酰胺结构二胺制备了具有不同取代基团的聚酰胺-酰亚胺薄膜, 考察了酰胺结构对薄膜力学、 耐热及尺寸稳定性的影响, 研究了聚集态结构与薄膜热膨胀行为的关系和规律. 该系列薄膜具有超高强度和优异的耐热性能, 拉伸强度高达280.5 MPa, 玻璃化转变温度在389~409 ℃, 并在30~300 ℃温度范围内表现出超低负膨胀, 热膨胀系数(CTE, ppm/℃, 即10 ⁶ cm·cm ^-1·℃ ^-1)在-3.05~-1.74 ppm/℃之间. 聚集态分析结果表明, 酰胺结构使分子链间形成了强氢键相互作用, 分子链在薄膜面内方向高度有序取向, 并在膜厚方向堆积更为紧密, 使薄膜表现出热收缩现象. 通过不同体积大小的取代基团进一步调控分子链间相互作用及排列堆积, 可实现薄膜在高温下近乎零尺寸形变, 为设计制备超低膨胀聚合物基板材料提供了新思路.     

A new database and benchmark of the bond energies of noble-gas-containing molecules

We have developed a new database of structures and bond energies of 59 noble-gas-containing molecules. The structures were calculated by CCSD(T)/aug-cc-pVTZ methods and the bond energies were obtained using the CCSD(T)/complete basis set method. Many wavefunction-based and density functional theory methods have been benchmarked against the 59 accurate bond energies. Our results show that the MPW1B95, B2GP-PLYP, and DSD-BLYP functionals with the aug-cc-pVTZ basis set excel in predicting the bond energies of noble-gas molecules with mean unsigned errors (MUEs) of 2.0 to 2.1 kcal/mol. When combinations of Dunning's basis sets are used, the MPW1B95, B2GP-PLYP, DSD-BLYP, and BMK functionals give significantly lower MUEs of 1.6 to 1.9 kcal/mol. Doubly hybrid methods using B2GP-PLYP and DSD-BLYP functionals and MP2 calculation also provide satisfactory accuracy with MUEs of 1.4 to 1.5 kcal/mol. If the Ng bond energies and the total atomization energies of a group of 109 main-group molecules are considered at the same time, the MPW1B95/aug-cc-pVTZ single-level method (MUE = 2.7 kcal/mol) and the B2GP-PLYP and DSD-PLYP functionals with combinations of basis sets or using the doubly hybrid method (MUEs = 1.9-2.2 kcal/mol) give the overall best result.