分子晶体中的几种分子间相互作用

描述了ＨＥＫ－ＤＤＱ，［Ｃｏ（Ｃ_５Ｈ_５）_２］［Ｎｉ（ｄｍｉｔ）_２］，ＢＢＢＴ－ＤＴＴ三个晶体结构中的π…π；Ｓ…Ｓ；Ｂｒ…Ｂｒ分子间相互作用，讨论了分子晶体中的分子间相互作用的材料化学意义。     

吗啉离子液晶的合成和介晶行为

一系列吗啉离子液晶被合成,包括N-烷基-N-甲基吗啉类盐(Mor1, nX, n = 10, 12, 14, 16, X = BF4-) 和酸性N-十六烷基吗啉类盐(Mor16X, X = BF4-, CH3SO3- and p-CH3C6H4SO3-) 。它们的介晶性质通过差示扫描量热仪,偏光显微镜表征。N-十六烷基-N-甲基吗啉氟硼酸离子液晶的分子结构通过单晶衍射和变温小角X射线衍射进行研究。结果表明,氟硼酸阴离子利于介晶化合物的形成和稳定,且它与吗啉阳离子形成的氢键导致了介晶相变过程中的构造变化。     

Enabling Control over Mechanical Conformity and Luminescence in Molecular Crystals: Interaction Engineering in Action

Molecular crystals of π-conjugated molecules are of great interest as the highly ordered dense packing offers superior charge and exciton transport compared with its amorphous counterparts. However, integration into optoelectronic devices remains a major challenge owing to its inherently brittle nature. Herein, control over the mechanical conformity in single crystals of pyridine-appended thiazolothiazole derivatives is reported by modulating the molecular packing through interaction engineering. Two polymorphs were prepared by achieving control over the thermodynamic/kinetic factors of crystallization; one of the polymorphs exhibits elastic bending whereas the other is brittle. The control over the bending ability was achieved by forming co-crystals with hydrogen/halogen bond donors. A seamless extended crisscross pattern with respect to the bend plane through a ditopic hydrogen-bonding motif showed the highest compliance towards mechanical bending, whereas the co-crystals with a layered crisscross arrangement with segregated layers of co-formers exhibit slightly lower bending conformity. These results update the rationale behind the plastic/elastic bending in molecular crystals. The co-crystals of ditopic halogen bond co-assemblies are particularly appealing for waveguiding applications as the co-crystals blend high mechanical flexibility and luminescence properties. The hydrogen bonded co-crystals are non-emissive in nature owing to excited state proton transfer dynamics. The rationale behind the fluorescence properties of these materials was also established from DFT calculations in a quantum mechanics/molecular mechanics (QM/MM) framework.     

Manipulating the Ultralong Organic Phosphorescence of Small Molecular Crystals

Ultralong organic phosphorescence (UOP) of metal-free organic materials has received considerable attention recently owing to their long-lived emission lifetimes, and the fact that they present an attractive alternative to persistent luminescence in inorganic phosphors. Enormous research effort has been devoted on improving UOP performance in metal-free organic phosphors by promoting the intersystem crossing (ISC) process and suppressing the non-radiative decay of triplet state excitons. This minireview summarizes the recent advances in the rational approaches for manipulating the UOP properties of small molecular crystals, such as phosphorescence lifetime, efficiency, and emission colors. Finally, the present challenges and future development of this field are proposed. This review will provide a guideline to rationally design more advanced metal-free organic phosphorescence materials for potential applications.     

Studying Microstructure in Molecular Crystals With Nanoindentation: Intergrowth Polymorphism in Felodipine

Intergrowth polymorphism refers to the existence of distinct structural domains within a single crystal of a compound. The phenomenon is exhibited by form II of the active pharmaceutical ingredient felodipine, and the associated microstructure is a significant feature of the compound’s structural identity. Employing the technique of nanoindentation on form II reveals a bimodal mechanical response on specific single‐crystal faces, demonstrating distinct properties for two polymorphic forms within the same crystal.     

Crack Formation and Propagation in Molecular Dynamics Simulations of Polymer Liquid Crystals

In recent papers we have used statistical mechanics to predict multiple phase formation in polymer liquid crystals (PLCs).^[1, 2] Now we have performed molecular dynamics simulations of PLC copolymers as materials consisting of LC islands in flexible matrices. A method for creating such materials on a computer is described. The overall concentration of the LC units, island size, and spatial distribution of the islands (random, in rows, and evenly distributed throughout the material) were varied. Crack formation and propagation as a function of these parameters were investigated. The local concentration of LC units in each chain has been defined. We found that the probability of a crack initiation site goes symbiotically with the local LC concentration. The first small crack is sometimes a part of the path through which the material breaks, however, although several small cracks may evolve at first, some of these never evolve into larger cracks since crack arrest occurs. The results can be used for creation of real materials with improved mechanical properties.     

Molecular Forcefield Methods for Describing Energetic Molecular Crystals: A Review

Energetic molecular crystals are widely applied for military and civilian purposes, and molecular forcefields (FF) are indispensable for treating the microscopic issues therein. This article reviews the three types of molecular FFs that are applied widely for describing energetic crystals—classic FFs, consistent FFs, and reactive FFs (ReaxFF). The basic principle of each type of FF is briefed and compared, with the application introduced, predicting polymorph, morphology, thermodynamics, vibration spectra, thermal property, mechanics, and reactivity. Finally, the advantages and disadvantages of these FFs are summarized, and some directions of future development are suggested.     

Nanoindentation in Crystal Engineering: Quantifying Mechanical Properties of Molecular Crystals

Nanoindentation is a technique for measuring the elastic modulus and hardness of small amounts of materials. This method, which has been used extensively for characterizing metallic and inorganic solids, is now being applied to organic and metal–organic crystals, and has also become relevant to the subject of crystal engineering, which is concerned with the design of molecular solids with desired properties and functions. Through nanoindentation it is possible to correlate molecular‐level properties such as crystal packing, interaction characteristics, and the inherent anisotropy with micro/macroscopic events such as desolvation, domain coexistence, layer migration, polymorphism, and solid‐state reactivity. Recent developments and exciting opportunities in this area are highlighted in this Minireview.     

阴离子对构筑锌的肼配位卤族化合物的影响

采用含桥联双齿配体的过渡金属配合物来构筑多维无穷结构的研究是近年来晶体工程领域的一个热点。已经发现的结构有无穷链式、金刚石型、立方、梯式、蜂窝式、螺旋梯状与砖墙式等多种几何构型。其中一维无穷链式结构是最简单的一种构型，它不仅是理论模拟多维结构的最简模型，而且是构筑其他多维结构如分子梯式与二维层状结构的基元。     

硝酸酯增塑剂力学性能和界面相互作用的分子动力学模拟

运用分子动力学(MD)方法, 模拟研究了硝化甘油(NG)及其与硝化三乙二醇(TEGDN)组成的硝酸酯增塑剂的低温力学性能. 结果表明, NG/TEGDN混合体系较NG单组分体系的刚性减弱, 延展性和各向同性增强. 结合能计算和径向分布函数分析揭示了混合型硝酸酯增塑剂组分之间的相互作用及其本质.     

Effect of Alkyl Groups in Pyrene Chromophore on the Mechanical Response of Pyrene‐Octafluoronaphthalene Co‐Crystals

Changes in the photophysical properties of pyrene ( Py )‐octafluoronaphthalene ( OFN ) co‐crystals ( Py ? OFN ) upon mechanical stimuli are described herein. The Py ? OFN co‐crystal showed a mechano‐induced bathochromic shift in emission, and a similar tendency was observed for the 1,3,6,8‐tetramethylpyrene‐ OFN co‐crystal. These shifts are due to disruption of the microscopic molecular orientation in the co‐crystal, which allows for excimer formation. In sharp contrast to the parent Py ? OFN and methyl‐substituted Py ‐ OFN co‐crystals, no mechano‐induced bathochromic shift was observed when longer alkyl chains were introduced to the 1‐, 3‐, 6‐, and 8‐positions of the Py chromophore. This photophysical opposability against mechanical stimuli could be explained by the orthogonally oriented alkyl groups on the Py ring, which existed between two Py cores like pillars. This fixed OFN to maintain the face‐to‐face alternatively stacked structure of the co‐crystal and thus prevented the formation of the Py excimer. The pillar effect demonstrated herein provides a rational design for co‐crystalline systems that are photophysically stable against mechanical stresses.     

Nematic Liquid Crystals for Active Matrix Displays: Molecular Design and Synthesis

Substances forming calamitic mesophases have been known for more than 100 years but only the recent, rapid advance in active matrix liquid crystal display (AM‐LCD) technology helped these materials to achieve the crucial position in flat panel display technology they hold today. Due to their high contrast, large viewing angle, and rapid switching times, modern AM‐LCDs offer a superior picture quality even compared to conventional cathode ray tubes. Their flatness, low weight, and low energy consumption render them the technology of choice for all kinds of portable devices. Some of the future promises of AM‐LCD technology are centered around the development of liquid crystalline materials for the different subtypes of active matrix applications. This development is aimed, on the one hand, towards improved electrooptical and viscoelastic properties; on the other hand, the increasing performance of LCDs leads to extremely stringent reliability demands on the liquid crystals. Responding to these high standards of performance and quality, most liquid crystals for contemporary AM‐LCD applications are multiply fluorinated compounds with very high purities, as is typical for materials used in the electronics industry. The synthesis of these superfluorinated materials (SFMs) often requires specialized methods, which, in several cases, had to be introduced for the first time into the canon of industrial production. The immense market pressure, as well as the rapid advance of AM‐LCD technology on the side of the display manufacturers, urges an increasing pace of the materials development. This demand for new materials can no longer be fulfilled by conventional trial‐and‐error approaches. As in the pharmaceutical industry, in the search for new, superior liquid crystals, the purely empirical methods are increasingly supported by a rational design based on computational methods.     

X-ray diffraction investigation of siloxanes. I. Effects of organic substituents at the silicon atoms on the structure of acyclic trisiloxane-1,5-diols and on formation of different hydrogen bond systems

The molecular and crystal structure of four acyclic trisiloxane compounds, which differ in substituents at the silicon atoms (Ph-phenyl, mPh-methoxyphenyl, 2mPh-dimethoxyphenyl), was investigated by X-ray diffraction analysis. Due to intermolecular hydrogen bonding between the oxygen atoms of the diol fragments, the crystal structure of 1,1,5,5-tetramethyl-3,3-diphenyl-1,3,5-trisiloxane-1,5-diol (C₁₆H₂₄O₄Si₃) (I) is a double chain architecture with hydrogen-bonded dimeric motifs of C(8)R ₄ ⁴ (12) type in graph set representation. In 1,1,5,5-tetramethyl-3,3-(2-methoxybenzo)-1,3,5-trisiloxane-1,5-diol (C₁₈H₂₈O₆Si₃) (II) and 1,1,5,5-tetramethyl-3,3-(2,6-dimethoxybenzo)-1,3,5-trisiloxane-1,5-diol (C₂₀H₃₂O₈Si₃) (III), a double chain structure with a graph set R ₃ ³ (8)D ₃ ³ (10) is formed. In contrast to I–III, 1,1,3,3,5,5-hexaphenyl-1,3,5-trisiloxane-1,5-diol (C₃₆H₃₂O₄Si₃) (IV) has an intramolecular hydrogen bond S(8). The independent molecules are joined by O-H...O intermolecular hydrogen bonds into centrosymmetrical dimers; the system of hydrogen bonds in general may be described as S(8)R ₄ ⁴ (8).     

Monolayer Two‐dimensional Molecular Crystals for an Ultrasensitive OFET‐based Chemical Sensor

The sensitivity of conventional thin‐film OFET‐based sensors is limited by the diffusion of analytes through bulk films and remains the central challenge in sensing technology. Now, for the first time, an ultrasensitive (sub‐ppb level) sensor is reported that exploits n‐type monolayer molecular crystals (MMCs) with porous two‐dimensional structures. Thanks to monolayer crystal structure of NDI3HU‐DTYM2 (NDI) and controlled formation of porous structure, a world‐record detection limit of NH₃ (0.1 ppb) was achieved. Moreover, the MMC‐OFETs also enabled direct detection of solid analytes of biological amine derivatives, such as dopamine at an extremely low concentration of 500 ppb. The remarkably improved sensing performances of MMC‐OFETs opens up the possibility of engineering OFETs for ultrasensitive (bio)chemical sensing.     

Photoinduced Ratchet‐Like Rotational Motion of Branched Molecular Crystals

Photomechanical molecular crystals can undergo a variety of light‐induced motions, including expansion, bending, twisting, and jumping. The use of more complex crystal shapes may provide ways to turn these motions into useful work. To generate such shapes, pH‐driven reprecipitation has been used to grow branched microcrystals of the anthracene derivative 4‐fluoroanthracenecarboxylic acid. When these microcrystals are illuminated with light of λ=405 nm, an intermolecular [4+4] photodimerization reaction drives twisting and bending of the individual branches. These deformations drive a rotation of the overall crystal that can be repeated over multiple exposures to light. The magnitude and direction of this rotation vary because of differences in the crystal shape, but a typical branched crystal undergoes a 50° net rotation after 25 consecutive irradiations for 1 s. The ability of these crystals to undergo ratchet‐like rotation is attributed to their chiral shape.     

Inherent Ethyl Acetate Selectivity in a Trianglimine Molecular Solid

Ethyl acetate is an important chemical raw material and solvent. It is also a key volatile organic compound in the brewing industry and a marker for lung cancer. Materials that are highly selective toward ethyl acetate are needed for its separation and detection. Here, we report a trianglimine macrocycle ( TAMC ) that selectively adsorbs ethyl acetate by forming a solvate. Crystal structure prediction showed this to be the lowest energy solvate structure available. This solvate leaves a metastable, “templated” cavity after solvent removal. Adsorption and breakthrough experiments confirmed that TAMC has adequate adsorption kinetics to separate ethyl acetate from azeotropic mixtures with ethanol, which is a challenging and energy-intensive industrial separation.     

Photomechanical Organic Crystals as Smart Materials for Advanced Applications

Photomechanical molecular crystals are receiving much attention due to their efficient conversion of light into mechanical work and advantages including faster response time; higher Young's modulus; and ordered structure, as measured by single-crystal X-ray diffraction. Recently, various photomechanical crystals with different motions (contraction, expansion, bending, fragmentation, hopping, curling, and twisting) are appearing at the forefront of smart materials research. The photomechanical motions of these single crystals during irradiation are triggered by solid-state photochemical reactions and accompanied by phase transformation. This Minireview summarizes recent developments in growing research into photoresponsive molecular crystals. The basic mechanisms of different kinds of photomechanical materials are described in detail; recent advances in photomechanical crystals for promising applications as smart materials are also highlighted.     

500微米沸石分子筛单晶的制备方法

介绍了20世纪如年代以来500μg以上的沸石分子筛单晶的六种制备方法，包括类区域融化法、植入晶种法、有机热合成法、块状原料溶解法、氟离子效应合成法和双硅源法。这些方法通过控制反应体系中晶核的形成数量，然后在这些极少数晶核的基础上培养出沸石分子筛大单晶。     

Metal-like Ductility in Organic Plastic Crystals: Role of Molecular Shape and Dihydrogen Bonding Interactions in Aminoboranes

Ductility is a common phenomenon in many metals but is difficult to achieve in molecular crystals. Organic crystals bend plastically on one or two face-specific directions but fracture when stressed in any other arbitrary directions. An exceptional metal-like ductility and malleability in the isomorphous crystals of two globular molecules, BH₃NMe₃ and BF₃NMe₃, is reported, with characteristic tensile stretching, compression, twisting, and thinning. The mechanically deformed samples, which transition to lower symmetry phases, retain good long-range order amenable to structure determination by single-crystal X-ray diffraction. Molecules in these high-symmetry crystals interact through electrostatic forces (B⁻−N⁺) to form columnar structures with multiple slip planes and weak dispersive forces between columns. On the other hand, the limited number of facile slip planes and strong dihydrogen bonding in BH₃NHMe₂ negates ductility. Our study has implications for the design of soft ferroelectrics, solid electrolytes, barocalorics, and soft robotics.     

Kitaigorodsky Revisited: Polymorphism and Mixed Crystals of Acridine/Phenazine

Non‐stoichiometric molecular mixed crystals have potential as functional materials, the properties of which can be tailored by rationally changing their composition. The guidelines for their preparation were summarized over thirty years ago by Alexander Kitaigorodsky. Here those principles are revised in light of new studies on the acridine/phenazine system, and solvent‐assisted grinding is presented as a convenient synthetic procedure to afford a more homogeneous product than traditional solvent‐evaporation methods. Finally, the proposed prerequisite of crystal isostructurality/isomorphicity for the pure compounds, which seems to be violated in the present case, is discussed.