Theoretical Study On Detonation Performance And Elimination Reaction Mechanism Of Several B,N-containing Compounds

B,N-containing compounds are widely applied as energetic materials and optoelectronic materials.In this thesis,the density functional theory(DFT)and the complete active space self-consistent field and its second-order perturbation(CASPT2/CASSCF)methods were employed to systematically study the detonation performance and the stability of several B,N-containing energetic compounds,as well as the elimination mechanism of one B,N-heterocycle molecule.The main results are summarized as follows:(1)The relationship of the structure and stability,as well as the relationship of the structure and the exothermic performance of B,N-containing chain compounds.The calculated results demonstrate that the energies of the chain B₂N₄,B₂N₆,and B₂N₈ isomers increase as the number of consecutive nitrogen atoms increases.The structures of low-energy isomers are characterized by B-N alternation pattern or the maximum three consecutive N atoms at the end of the chain.The values of bond dissociation energy(BDE)indicate that B atoms can stabilize N-rich molecules more effectively than C atoms.Besides,the combustion of B,N-containing compound releases more heat than that of C,N-containing compound under well-oxygenated condition.(2)Designing a novel B,N-containing compound(E)-1,2-diamino-1,2-dinitrodiboron(DANB)as energetic material with good stability.The obtained results show that DANB has large heat of formation(HOF)(2013.5 k J/mol),specific enthalpy of combustion(-26.4 k J/g),heat of detonation(5476.0 cal/g)and crystal density(1.85 g/cm³),which lead to the surprising detonation performance(detonation velocity=10.72 km/s,detonation pressure=51.9 GPa)greater than those of the most common explosives such as FOX-7,CL-20,HMX,and PETN.More importantly,the BDE of DANB(357.8 k J/mol)is higher than those of FOX-7,CL-20,HMX,and RDX,implying the excellent thermodynamic stability of DANB.(3)The influence of replacing C?C with B?N on the stability and detonation performance of energetic compounds.The results indicate that substituting one,two,and three C?C with B?N in 2,4,6-trinitrotoluene(TNT)can reduce the HOMO-LUMO energy gap,increase the crystal density,and enhance the detonation performance.Among these three types of energetic compounds,the energetic compounds containing only one B?N exhibit the best detonation performance.Since the BDEs follow the order of BDE(B?N)>BDE(C?N)>BDE(N?N),the energetic compound with the nitro group connecting the B atom or C atom holds the best thermodynamic stability.In terms of the stability,the detonation performance,and the sensitivity,the energetic compound containing only one B?N and the nitro group attached to the B atom or C atom is the most promising candidate.(4)Mechanism of the thermal/photo eliminations of a B,N-heterocycle compound6,7-dihydro-5⁴-benzo[d]pyrido[2,1-f][1,2]azaborininr(B4).By studying the elimination pathways of B4 on the ground state(S₀)and the first excited state(S₁),we found that the BH₃ elimination and H₂ elimination are two competing reactions with good selectivity:the BH₃ elimination reaction(with a barrier of 2.42 e V on the ground state)prefers to proceed with larger probability than the H₂ elimination upon heating,while the photoelimination of H₂ may take place facile due to the almost barrierless pathway on S₁ state.In addition,we have located an energetically available conical intersection(S₁/S₀)_X-1,which allows for ultrafast S₁?S₀ decay and subsequently generating of ground-state product C4.The results of this thesis provide a theoretical basis for the design and synthesis of B,N-containing compounds,and are helpful to understand the complex photochemical processes of B,N-heterocycle compounds.