Regioisomeric N-C functionalization of an asymmetric N-rich framework: a promising pathway to heat-resistant energetic materials

Energetic materials with high decomposition temperatures have wide applications in extreme environments such as spacecraft separation systems and drilling engineering. In this study, regioisomeric N-functionalization of an asymmetric pyrazole-triazole backbone yielded a highly thermostable energetic compound, 1-methyl-3-(1-methyl-3,4-dinitro-1H-pyrazol-5-yl)-5-nitro-1H-1,2,4-triazole (4), alongside a trace amount of its regioisomer, 1-methyl-5-(1-methyl-4,5-dinitro-1H-pyrazol-3-yl)-3-nitro-1H-1,2,4-triazole (5). The structures were confirmed by single-crystal X-ray analysis. At a decomposition temperature of 337 °C, compound 4 competes effectively with its isomer 5 (T_d, 189 °C) and with other reported N-methyl functionalized nitrogen-rich azoles. Additionally, its low sensitivity to impact and friction adds value as a heat-resistant energetic compound. Compared to analogous N-C functionalized bisazoles I (T_d = 275 °C) and Me₂TNBI (T_d = 258 °C), the thermal behaviors of 4 and 5 highlight the synergistic effect of the asymmetric backbone and regioisomeric N-C functionalization on designing heat-resistant energetic materials.