Power of sulfur – Chemistry, properties, laser ignition and theoretical studies of energetic perchlorate-free 1,3,4-thiadiazole nitramines

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The chemistry of lead-, azide- and perchlorate-free photosensitive energetic materials suitable for laser-ignition systems is an emerging field of research with a broad range of applications. To develop less toxic materials that would be sufficiently thermostable, safe, and sensitive enough to be ignited by low-power laser, is a formidable challenge. In this work, we designed, prepared, and studied properties of new sulfur-containing energetic molecules (SEMols), based on novel N-(1,3,4-thiadiazol-2-yl)nitramide explosophore. Newly synthesized energetic compounds N-(5-nitro-1,3,4-thiadiazol-2(3H)-ylidene)-nitramide (L1) and N5,N5′-dinitro-[2,2′-bi(1,3,4-thiadiazole)]-5,5′(4H,4′H)-diimine (L4) were found to be more thermostable than their sulfur-free 1,3,4-oxadiazole analogues. In small-scale detonation experiments, L1, L4, and C7 showed better brisance than TNT. Perchlorate-free complex C7 was found to have low-power laser igniting properties, showing an ignition delay time of 11 ms and threshold ignition energy of 12.0 mJ (at 915 nm irradiation). Extensive crystal-level (328-atom super-cell) ab-initio molecular dynamics and TD-DFT calculations were performed to study the laser ignition mechanism of C7. Based on our hypothesis, this photo-thermal ignition is taking place via sequential multi-photon absorption, with energy transfer to vibrational motions in this molecule. We suggest that SEMols, such as C7, can open a new platform for the development of novel energetic materials that have a potential for integration into laser-based safe energetic components in civil, aerospace, and defense applications.