Substituent engineering of pyrazolo-tetrazine N-oxide (PTZO) derivatives toward high-energy low-sensitivity energetic materials: A DFT study.

CONTEXT: Achieving energetic materials with both outstanding detonation performance and low-mechanical sensitivity remains a long-standing objective in the field of energetic materials. In this study, a library of 77 pyrazolo-tetrazine oxide (PTZO)-based derivatives was designed and systematically evaluated. Density functional theory (DFT), together with crystal-density prediction and detonation-property calculations, was employed to investigate their electronic characteristics, thermodynamic behavior, energetic performance, and sensitivity. The results indicate that the nature of the substituents has a pronounced influence on the overall properties of the PTZO derivatives. The incorporation of highly energetic groups, especially -C(NO₂)₃, markedly enhances the heats of formation, crystal densities, detonation velocities, and detonation pressures. In contrast, the introduction of the -NHNH₂ group effectively lowers impact sensitivity without sacrificing energetic performance. Furthermore, electrostatic potential (ESP) and interaction region indicator (IRI) analyses demonstrate that both the surface electrostatic distribution and intramolecular weak interactions play important roles in determining the stability and sensitivity of the designed compounds. Comprehensive evaluation identifies K1, K5, L1, L3, and L4 as the most promising candidates because of their excellent balance between energetic performance and safety. More importantly, this work establishes the structure-property relationship between substituent electronic effects, molecular electronic structure, thermodynamic properties, detonation performance, and sensitivity, providing an effective strategy for the rational design of high-energy, low-sensitivity energetic materials. METHODS: Density functional theory (DFT) calculations, combined with thermodynamic, detonation-performance, and wavefunction analyses, were carried out to systematically investigate the electronic structures, energetic properties, and sensitivity of the designed PTZO derivatives.