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The balance between pertinence and universality of high value-added energetic materials has gained importance in recent years. Inspired by the efficient working mechanism of stem cells, an innovative energetic material concept, multifunctional modular energetic materials (MMEMs), with the ability of quantity production and multifunctional uses was first proposed. A machine learning-assisted high-throughput screening system was developed and applied to guide the discovery of MMEMs, and promising energetic compounds were rapidly targeted and synthesized. These compounds exhibited a satisfactory density, thermal properties, detonation performance and sensitivity. Furthermore, they can be easily synthesized to maintain the "energetic stem cell pool" and can undergo "differentiation" for functioning as various compounds such as crystal explosives, cast explosive carriers, energetic binders, and plasticizers through different processing forms/different formulae as needed. It is anticipated that the findings of this study will open up a new research direction of application-oriented energetic materials. [ABSTRACT FROM AUTHOR]

The prediction of crystal structures is of great significance in the community of energetic materials since the crystal packing pattern is closely linked to the energetic and safety features. Here, we developed a tailor-made polarizable force field (TMPFF) calibrated by the benchmarks obtained from ab initio methods and applied it with the USPEX evolutionary algorithm to predict crystal structures from energetic molecular structures. The results showed that the prediction results of three polymorphs of hexaazaisowurtzitane (CL-20) all agree well with experimental measurements, for both lattice parameters and packing patterns. This work provides a new solution to predict polymorphs of CHON-based energetic molecules with high accuracy and good efficiency and shall accelerate the cognition process of new energetic crystals by theoretical approaches prior to experimental synthesis. [ABSTRACT FROM AUTHOR]

In recent years, organic radicals have gained considerable attention because they open opportunities for new-generation electronics which may integrate spin, magnetic and quantum mechanical effects. However, air stable organic radicals in the solid state, which can be practically applied, remain a great challenge in chemistry. Herein, we choose N-heptanamido triarylamine as a fragment which can produce radicals upon light irradiation, phenothiazine as a donor (D) unit, and 3-ethylrhodanine or 1,3-indanedione as an acceptor (A) unit, and then connect them in a conjugated manner. The results of 1H-NMR spectroscopy, DFT calculations, EPR measurements, AFM and photophysical characterization revealed that the introduction of the D unit could significantly increase spin delocalization and then the stability of the light-triggered TPA radicals in chloroform solution. These radicals can be maintained in the solid state. More importantly, these become stable radicals with a half-life of approximately one month under ambient conditions due to the stronger intermolecular aggregation resulting from the introduction of the A unit. This work provides a new approach for obtaining air-stable radicals in the solid-state from organic radicals in solution. [ABSTRACT FROM AUTHOR]

First principles investigation and Hirshfeld surface analysis of 1,3,5-triamino-2,4,6-trinitrobenzene (TATB) crystals have been carried out. The geometrical and electronic structures of TATB molecules in the crystal and gas phases were compared. The Hirshfeld surface analysis of the TATB crystal structure shows that the intermolecular H⋯O interactions make important contributions in stabilizing the TATB crystal, while other intermolecular H⋯N and H⋯C interactions, O⋯O, N⋯O, C⋯O, and C⋯N close contacts also make contributions. QTAIM analyses of the intermolecular interactions in the molecular pairs confirm the presence of these intermolecular interactions based on Hirshfeld surface analyses, indicating that these intermolecular interactions play important roles in the crystal. The reason why the TATB crystal adopts a high energy conformer in which the NO2 and NH2 groups are coplanar with the benzene ring is elaborated. The cooperativity between hydrogen bonding and π⋯π interactions in the TATB crystal is verified and illustrated. [ABSTRACT FROM AUTHOR]

Crystal structure predictions are significant and meaningful for the design of high energy materials since different packing modes can greatly influence their properties, such as energy and safety. In view of the difficulty of organic crystal structure predictions, an alternative strategy was proposed in this work based on the packing similarity of "homologous crystals". As a case study, the crystal structures of two energetic N-oxides were accurately and rapidly predicted by this strategy, that is, using their O-free analogues with known structures to generate initial crystals. Two rules, molecular similarity and electrostatic matching, were put forward to ensure the packing similarity in the practical applications of crystal structure predictions. Despite the limited number of "homologous crystals" of energetic N-oxides, this study is envisioned to provide a new approach to predict crystal structures of other high energy materials. [ABSTRACT FROM AUTHOR]

Currently, crystal engineering has attracted much attention as a promising strategy to balance the energy and sensitivity of explosives, such as energetic–energetic co-crystals. A deep understanding of the intermolecular interactions in explosive crystals from a microscopic point of view is meaningful for the development of low-sensitivity and high-energy (LSHE) explosives. Herein, the cooperativity of hydrogen bonds (HBs) in the nitramide (NA) crystal was quantitatively investigated with the aid of computational methods as a prototypical study of LSHE crystals. Two types of HB interactions were identified via both geometry and electron density analysis, and the electrostatic interactions dominantly contribute to the HB formation. The cooperativities of the single HB type and induced by other intermolecular interactions were quantified in various structural models, including linear clusters and layer fragments. The deconstruction of the NA crystal shows that the interaction energy for crystal stabilization was reduced by about 21% in comparison with that of the dimer as a result of an overall anti-cooperativity of the HB interactions, which is energetically unfavored for the formation of explosive crystals due to the weakening of the intermolecular interactions. This prototypical study is aimed to establish a theoretical strategy for further exploration of intermolecular interaction cooperativities in practical LSHE explosives, and is envisioned to open a new perspective to improve the knowledge of the crystal structure-sensitivity relationship. [ABSTRACT FROM AUTHOR]

As a crucial factor, crystal morphology significantly influences the energy and safety properties of energetic materials (EMs). Theoretical prediction of crystal morphology is helpful for scientifically engineering the shape of EM crystals. Currently, the attachment energy (AE) model has been the most widely used method of crystal morphology prediction in the field of EMs. However, the calculation details of modified AE in solution and the physical meaning of some corrected parameters are still unclear, sometimes leading to discrepant predicted results even for the same EM. Here, HMX (1,3,5,7-tetranitro-1,3,5,7-tetrazocane) was taken as a case study and the details of AE calculation were systematically explored. The formula of AE in solution was corrected and a new functional form was proposed. The growth morphology of a HMX crystal in acetone solution was predicted, which is similar to those of the occupancy model, the spiral growth model, and the interfacial structure analysis model. The results reported in this contribution are aiming at the development of a more reasonable and accurate method for predicting the crystal shape of EMs. [ABSTRACT FROM AUTHOR]

Understanding the switching mechanism of helical molecular cages is critical in regulating their functions of asymmetric catalysis and enantioseparation. The helical inversion of a three-tiered stacked architecture was investigated by employing molecular dynamics simulations combined with free-energy calculations. A two-dimensional free-energy landscape characterizing the spinning processes of the top and bottom tiers around the z axis was determined using the extended adaptive biasing force method. The free-energy barrier in the least free-energy pathway was estimated to be 17.6 kcal mol−1, in excellent agreement with experimental measurements. Further analysis revealed that the barrier was caused by geometric deformation, weakening of π–π stacking between aromatic rings, and the re-orientation of polarized amine moieties. The present contribution takes a step toward understanding the dynamic helicity-based functions related to asymmetric reactions and optical resolution. [ABSTRACT FROM AUTHOR]

The structure and dynamics of the nitromethane–water (NM–WT) binary mixture surrounding single walled carbon nanotubes (SWNTs) have been investigated by molecular dynamics simulations. The simulation trajectories show that the NM molecules can be selectively adsorbed both outside the surface and inside the cavity of SWNTs mainly dominated by van der Waals attractions because SWNTs have a higher binding affinity for NM than WT. The binding energies of SWNTs with NM and WT obtained from electronic structure calculations at the M06-2X/6-31+G* level are 15.31 and 5.51 kcal mol−1, respectively. Compared with the SWNT exterior, the selective adsorption of NM is preferentially occurred in the SWNT interior due to the hydrophobic interactions and the dipole–dipole interactions, which induces the decrease of the hydrogen-bond number of NM with WT and ordered structures of NM with preferred intermolecular orientation in the SWNT cavity. Furthermore, the selective adsorption dynamics of NM from the aqueous solution is regardless of the chirality and radius of SWNTs. The SWNT radius plays a negligible role in the mass density distributions of NM outside the SWNTs, while the mass density of NM in the SWNT interior decreases gradually as the SWNT radius increases. The structural arrangements and intermolecular orientations of NM in the SWNT cavity are greatly dependent on the SWNT radius due to the size effect. [ABSTRACT FROM AUTHOR]