Guo-Sheng(石国升) a) , Wang Zhi-Gang(王志刚) a) † , Zhao Ji-Jun(赵纪军) b) , Hu Jun(胡 钧) a) , and Fang Hai-Ping(方海平) a) ‡
The unreacted equation of state (EOS) of energetic materials is an important thermodynamic relationship to characterize their high pressure behaviors and has practical importance. The previous experimental and theoretical works on the equation of state of several energetic materials including nitromethane, 1,3,5-trinitrohexahydro-1,3,5-triazine (RDX), 1,3,5,7-tetranitro-1,3,5,7-tetrazacyclooctane (HMX), hexanitrostilbene (HNS), hexanitrohexaazaisowurtzitane (HNIW or CL-20), pentaerythritol tetranitrate (PETN), 2,6-diamino-3,5-dinitropyrazine-1-oxide (LLM-105), triamino-trinitrobenzene (TATB), 1,1-diamino-2,2-dinitroethene (DADNE or FOX-7), and trinitrotoluene (TNT) are reviewed in this paper. The EOS determined from hydrostatic and non-hydrostatic compressions are discussed and compared. The theoretical results based on ab initio calculations are summarized and compared with the experimental data.
The lowest-energy structures of Li-n-1, Lin and Li+n+1 clusters (n=20, 40) were determined from first-principles simulated annealing followed by geometry optimization within the density functional theory. The growth mechanism of Lin clusters is based on nested multiple polyhedron. Other atoms form pentagonal pyramid centered on the core polyhedron. From our first-principles calculations, the molecular orbital levels can be divided into several groups, which are in good agreement with the electron shells described by structureless jellium model. With the same amount of valence electrons, the number of ions and charge states in the Li clusters have only little effect on the electronic structures. Li-19, Li20, Li+21 and Li-39, Li40, Li+41 exhibit similar energy level distributions, respectively, indicating that the momentum order is the dominating factor for these clusters. The optical absorption spectra of Li-n-1, Lin and Li+n+1 (n=20, 40) clusters from time-dependent density functional theory calculations show giant resonance phenomenon and the simulated resonance peaks agree with experimental values. With same amount of valence electrons, the polarizability decreases with the number of ions and the optical resonance peaks blueshift as the ionic number increases.
Thermally activated delayed fluorescence (TADF), a unique molecular fluorescence mechanism, plays a key role in designing emitters of high efficiency. Carbon fullerenes such as C60 and C70 exhibit strong TADF with intensity even higher than that of the fluorescence, owing to their long lifetimes of triplet state and modest singlet-triplet energy gaps. It raises an intriguing question if other fullerene-like clusters have fluorescence and can host the TADF effect. Herein, by time-dependent density functional theory (TD-DFT) calculations, we explore the excited-states of the experimentally reported boron nitride cage clusters B12N12, B24N24 and B36N36, as well as compound clusters B12P12, Al12N12 and Ga12N12 with the same geometry as B12N12. Using the HSE06 hybrid functional, the predicted energy gaps of these fullerene-like clusters range from 2.83 eV to 6.54 eV. They mainly absorb ultraviolet light, and their fluorescence spectra are all in the visible regime, from 405.36 nm to 706.93 nm, including red, orange, blue, and violet emission colors. For the boron nitride cages, the energy gap of excited states increases with the cluster size, accompanied by a blue shift of emission wavelength. For the clusters with B12N12 geometry and different elemental compositions, the excited energy gap decreases as the atomic radius increases, leading to a red shift of emission wavelength. In addition, the HOMO and LUMO orbitals of these compound cage clusters distribute separately on different elements, resulting in small overlap of HOMO and LUMO wavefunctions. Consequently, these fullerene-like clusters exhibit small singlet-triplet energy differences below 0.29 eV, which is beneficial for the intersystem crossing between the excited singlet and triplet states and hence promote the TADF process. Our theoretical results unveil the fluorescence characteristics of cage clusters other than carbon fullerenes, and provide important guidance for precisely modulating their emission colors by controlling the cluster sizes and elemental compositions. These experimentally feasible fullerene-like compound clusters possess many merits as fluorophors such as outstanding stabilities, non toxicity, large energy gap, visible-light fluorescence, and small singlet-triplet energy gap. Therefore, they are promising luminescent materials for applications in display, sensors, biological detection and labelling, therapy, and medicine.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.