Polynitro [1,2,4] triazolo [4,3-b] pyridazine: a building block for superior-performance energetic materials

The design and synthesis of a high-energy-density material (HEDM) that simultaneously possesses high energy and low sensitivity is a challenging task. This study reports an effective strategy for constructing polynitro-substituted bicyclic fused ring frameworks. A series of polynitro [1,2,4] triazolo [4,3-b] pyridazine fused rings with nitrogen-rich NH₂/NHNH₂/NHOH groups were first synthesized by straightforward routes, and were characterized by chemical (NMR, MS, IR spectroscopy, and single-crystal X-ray diffraction) as well as experimental analysis (sensitivity towards friction, impact, and DSC-TGA test). Their detonation properties (detonation velocity, detonation pressure, etc.) were predicted by the EXPLO5 program. These new polynitro fused ring compounds were found to exhibit high density, high decomposition temperature, and acceptable impact and sensitivity, making them promising high-energy-density materials (HEDM). It is worth noting that the excellent energetic properties (density: 1.932 g cm⁻³, V_det: 9585 m s⁻¹; P_CJ: 41.8 GPa), superior to those of HMX (1,3,5,7-tetranitrotetraazacyclooctane), highlight compound 5 as the highest-performing bicyclic fused ring energetic compound reported to date. Computational considerations of 5 and 2,4,6-triamino-1,3,5-trinitrobenzene (TATB) suggest that its structural character provides a good balance between energy and safety (sensitivity: 36 J, 324 N). This work demonstrates the effectiveness of introducing polynitro groups into the multi-ring planar skeleton and provides a generalizable design synthesis strategy for developing new HEDMs.