Recent Progress in Polycyclic Aromatic Hydrocarbon‐Based Organic Co‐Crystals

Recently, the development of polycyclic aromatic hydrocarbon ( PAH )‐based organic co‐crystals has attracted increasing interest due to their unique packing modes, optic‐electronic properties and various potential applications in electronic, optic‐electronic and magnetic devices. In this account, we mainly discuss the definition, classification, packing patterns, preparation methods, and applications of PAH‐based co‐crystals. Specifically, the main categories of PAH‐based organic co‐crystals, the frequent methods to prepare them, three main packing patterns, their optical and electrical properties, and their potential applications will be presented. Finally, an outlook of this field is provided.     

Strength of the [Z–I···Hal]− and [Z–Hal···I]− Halogen Bonds: Electron Density Properties and Halogen Bond Length as Estimators of Interaction Energy

Bond energy is the main characteristic of chemical bonds in general and of non-covalent interactions in particular. Simple methods of express estimates of the interaction energy, E_int, using relationships between E_int and a property which is easily accessible from experiment is of great importance for the characterization of non-covalent interactions. In this work, practically important relationships between E_int and electron density, its Laplacian, curvature, potential, kinetic, and total energy densities at the bond critical point as well as bond length were derived for the structures of the [Z–I···Hal]⁻ and [Z–Hal···I]⁻ types bearing halogen bonds and involving iodine as interacting atom(s) (totally 412 structures). The mean absolute deviations for the correlations found were 2.06–4.76 kcal/mol.     

The competition of Y⋯o and X⋯n halogen bonds to enhance the group V σ‐hole interaction in the NCY⋯oPH3⋯NCX and OPH3⋯NCX⋯NCY (X,YF,Cl, and Br) complexes

The positive electrostatic potentials (ESP) outside the σ‐hole along the extension of O? P bond in O?PH₃ and the negative ESP outside the nitrogen atom along the extension of the C? N bond in NCX could form the Group V σ‐hole interaction O?PH₃?NCX. In this work, the complexes NCY?O?PH₃?NCX and O?PH₃?NCX?NCY (X, Y?F, Cl, Br) were designed to investigate the enhancing effects of Y?O and X?N halogen bonds on the P?N Group V σ‐hole interaction. With the addition of Y?O halogen bond, the V _{S, max} values outside the σ‐hole region of O?PH₃ becomes increasingly positive resulting in a stronger and more polarizable P?N interaction. With the addition of X?N halogen bond, the V _{S, min} values outside the nitrogen atom of NCX becomes increasingly negative, also resulting in a stronger and more polarizable P?N interaction. The Y?O halogen bonds affect the σ‐hole region (decreased density region) outside the phosphorus atom more than the P?N internuclear region (increased density region outside the nitrogen atom), while it is contrary for the X?N halogen bonds. © 2015 Wiley Periodicals, Inc.     

Multiple Multidentate Halogen Bonding in Solution,in the Solid State,and in the (Calculated) Gas Phase

The binding properties of neutral halogen‐bond donors (XB donors) bearing two multidentate Lewis acidic motifs toward halides were investigated. Employing polyfluorinated and polyiodinated terphenyl and quaterphenyl derivatives as anion receptors, we obtained X‐ray crystallographic data of the adducts of three structurally related XB donors with tetraalkylammonium chloride, bromide, and iodide. The stability of these XB complexes in solution was determined by isothermal titration calorimetry (ITC), and the results were compared to X‐ray analyses as well as to calculated binding patterns in the gas phase. Density functional theory (DFT) calculations on the gas‐phase complexes indicated that the experimentally observed distortion of the XB donors during multiple multidentate binding can be reproduced in 1:1 complexes with halides, whereas adducts with two halides show a symmetric binding pattern in the gas phase that is markedly different from the solid state structures. Overall, this study demonstrates the limitations in the transferability of binding data between solid state, solution, and gas phase in the study of complex multidentate XB donors.     

Brønsted Acid‐Catalyzed Cascade Reactions Involving 1,2‐Indole Migration

A cascade reaction of indoles with propargylic diols involving an unprecedented metal‐free 1,2‐indole migration onto an alkyne was carried out. DFT calculations support a mechanism consisting of a concerted nucleophilic attack of the indole nucleus with loss of water, followed by the 1,2‐migration and subsequent Nazarov cyclization. This Brønsted acid‐catalyzed protocol affords indole‐functionalized benzofulvene derivatives in high yields.     

Active‐Metal Template Synthesis of a Halogen‐Bonding Rotaxane for Anion Recognition

The synthesis of an all‐halogen‐bonding rotaxane for anion recognition is achieved by using active‐metal templation. A flexible bis‐iodotriazole‐containing macrocycle is exploited for the metal‐directed rotaxane synthesis. Endotopic binding of a Cu^I template facilitates an active‐metal CuAAC iodotriazole axle formation reaction that captures the interlocked rotaxane product. Following copper‐template removal, exotopic coordination of a more sterically demanding rhenium(I) complex induces an inversion in the conformation of the macrocycle component, directing the iodotriazole halogen‐bond donors into the rotaxane’s interlocked binding cavity to facilitate anion recognition.     

The dual role of halogen,chalcogen, and pnictogen atoms as Lewis acid and base: Triangular XBr:SHX:PH2X complexes (X = F,Cl, Br,CN, NC,OH, NH2, and OCH3)

Using ab initio calculations, we have investigated the possibility of formation of triangular XBr:SHX:PH₂X complexes, where X = F, Cl, Br, CN, NC, OH, NH₂, and OCH₃. These complexes are formed through the interaction of a positive electrostatic potential region (σ‐hole) on a molecule with the negative region in another one. The results show that the combined halogen, chalcogen, and pnictogen interactions can give rise to stable cyclic structures. The interaction energies of these complexes span over a wide range, from ?3.55 to ?24.93 kcal/mol. Nice quadratic correlations are found between the interaction energies and binding distances in the trimers. To understand the nature of the interactions in these complexes, molecular electrostatic potential and quantum theory of atoms in molecule analyses are performed. © 2015 Wiley Periodicals, Inc.     

Factors Affecting Grafting Density in Surface‐Initiated ATRP: A Simulation Study

In surface‐initiated atom transfer radical polymerization, knowledge of grafting density is of significant interest because it is one of the determining properties of grafted polymer. It is well known that not all of the immobilized initiators can grow into polymer chains. However, little is known about why this happens and what affects the grafting efficiency. The lack of information is partly due to the difficulty in experimental determination of grafting density on flat substrates. To circumvent the problem, Monte Carlo simulation with bond fluctuation model is used in this study to investigate the effects of various reaction conditions on the grafting density. The simulation results show lower grafting density when less deactivator is present. In systems with lower deactivator concentration, the number of monomer added per activation cycle is higher. Coupling this with close proximity of immobilized initiators results in chains initiated at earlier time to shield their neighboring initiator moieties from adding mono­mers, thus lowering the grafting density in such a system. These simulation results also provide an explanation to the seemingly conflicting trend reported in the literatures.

     

农村人口城市化中的时间配置决策研究

在Becker时间配置模型基础上,构建农村居民在城镇化进程中的行为决策模型,农村入口时间资源分配在农村活动、城市活动、教育活动和闲暇上,根据福利水平最大化的基本原则,分析农村人口城市化决策中影响因素.解释了农村人口城镇化和逆城镇化现象,发现城乡差异、教育影响、时间间接成本等因素是影响人们时间效率的主要因素,为提高全民福利水平,政府的农村政策应以增加农民收入为主,城市政策集中于城市基础设施和公共服务布局合理性方面.