Single Crystals Popping Under UV Light: A Photosalient Effect Triggered by a [2+2] Cycloaddition Reaction

The extremely rare examples of dynamic single crystals where excitation by light or heat induces macroscopic motility present not only a visually appealing demonstration of the utility of molecular materials for conversion of energy to work, but they also provide a unique opportunity to explore the mechanistic link between collective molecular processes and their consequences at a macroscopic level. Here, we report the first example of a photosalient effect (photoinduced leaping) observed with crystals of three coordination complexes which is induced by a [2+2] photocycloaddition reaction. Unlike a plethora of other dimerization reactions, when exposed to even weak UV light, single crystals of these materials burst violently, whereby they are propelled to travel several millimeters. The results point to a multistep mechanism where the strain energy that has been accumulated during the dimerization triggers a rapid structure transformation which ultimately results in crystal disintegration.     

Crystal Adaptronics: Mechanically Reconfigurable Elastic and Superelastic Molecular Crystals

Mechanically reconfigurable molecular crystals—ordered materials that can adapt to variable operating and environmental conditions by deformation, whereby they attain motility or perform work—are quickly shaping a new research direction in materials science, crystal adaptronics. Properties such as elasticity, superelasticity, and ferroelasticity, which are normally related to inorganic materials, and phenomena such as shape‐memory and self‐healing effects, which are well‐established for soft materials, are increasingly being reported for molecular crystals, yet their mechanism, quantification, and relation to the crystal structure of organic crystals are not immediately apparent. This Minireview provides a condensed topical overview of elastic, superelastic, and ferroelastic molecular crystals, new classes of materials that bridge the gap between soft matter and inorganic materials. The occurrence and detection of these unconventional properties, and the underlying structural features of the related molecular materials are discussed and highlighted with selected prominent recent examples.     

The Effect of Substrate on the Annealing of Poly(butylene succinate) Single Crystals

The morphological evolution of poly(butylene succinate) (PBS) solution‐grown single crystals during annealing was studied using hot‐stage atomic force microscopy. Their morphology changed with increasing temperature and annealing time. The annealing behavior and melting temperature were found to be affected by the substrate. Morphological changes occurred at a much lower temperature on an amorphous carbon film than that on a mica surface. Moreover, the pattern of morphological evolution of the single crystals on a carbon film was different from that on a mica surface. Since the PBS melt had a larger contact angle on the mica surface, these differences in the melting behavior were ascribed to the different interfacial interactions between the chain‐folded surface of the single crystal and the substrate.

     

TiO2单晶的表面光电压谱研究

TiO2由于其优异的光电性质及高的化学稳定性而受到广泛关注,并且被应用于有机污染物光降解[1]、太阳能光电转换[2]等诸多领域.由于制备方法不同,TiO2往往会呈现出不同的光电性质,尽管其晶型与粒度可能相差甚微[3].近年来研究表明,除晶型、粒度等因素外,表面原子排布在决定材料光电性质方面同样有重要贡献[4,5].本文采用表面光电压谱(SPS)及场诱导表面光电压谱(EFSPS)研究了TiO2单晶(001)面的光伏响应.     

去B链N端二肽(B_(1—2))猪胰岛素晶体结构的研究——单晶培养及X射线晶体学的分析

利用微量过饱和静置法,在柠檬酸缓冲液中培养出可供X射线结构分析用的去B链N端二肽(B_(1-2))猪胰岛素单晶。晶体衍射分辨率达到4.0A以上。晶体属于立方晶系,a=97.43A,空间群为P4_132(或P4_332),每个结晶学不对称单位含两个或三个去B链N端二肽(B_(1-2))猪胰岛素分子。本文对单位晶胞内六聚体之间和二聚体之间可能的堆积方式进行了讨论。     

Crystal Engineering of Energetic Materials: Co‐crystals of Ethylenedinitramine (EDNA) with Modified Performance and Improved Chemical Stability

In the area of energetic materials, co‐crystallization is emerging as a new technology for modifying or enhancing the properties of existing energetic substances. Ethylenedinitramine (EDNA) is a known energetic material which requires attention partly due to its chemical instability originating with its two highly acidic protons. In order to stabilize EDNA, a co‐crystallization approach targeting the acidic protons using a series of co‐crystallizing agents with suitable hydrogen‐bond acceptors was employed. Fifteen attempted co‐crystallizations resulted in eight successful outcomes and six of these were crystallographically characterized and all showed evidence of hydrogen bonds to the intended protons. Calculated detonation properties and experimental thermal and impact data for the co‐crystals were obtained and compared with those of pure EDNA. The co‐crystal of EDNA and 1,2‐bis(4‐pyridyl)ethylene was recognized as a more thermally stable alternative to EDNA while the co‐crystal of EDNA and pyrazine N,N′‐dioxide showed comparable detonation strengths (and much improved chemical stability) compared with that of EDNA. The co‐crystals EDNA:4,4′‐bipyridine and EDNA:pyrazine N,N′‐dioxide were found to be about 50 % less impact sensitive than EDNA, all of which illustrate how co‐crystallizations can be utilized for successfully modifying specific aspects of energetic materials.