Scaffold and Guest Regulation Metal-free Laser-Responsive Energetic Ionic Salts: Functional Construction and Transformation.

Laser initiation offers a safer and more controllable alternative to conventional initiation methods, with laser-responsive materials serving as the fundamental platform for such functional conversion. However, existing laser-responsive energetic compounds often rely on heavy metals and suffer from poor safety profiles, significantly limiting their practical deployment. The development of metal-free laser-responsive materials remains largely unexplored. This study introduces a design strategy that enables the construction and transformation of laser-responsive functions in metal-free energetic ionic salts (EISs) through the synergistic regulation of their oxygen balance via a fused-ring scaffold and guest ions. Following this strategy, a metal-free EIS (ES-1) was synthesized from a [5,1-c][1,2,4]pyrazolotriazine ring and a ClO4- anion. Subsequent transformations yielded ES-2 via guest anion exchange (ClO4- to NO3-) and ES-3 through functionalization. The distinct crystal packing, thermal stability, and energetic properties of ES-1, ES-2, and ES-3, as determined by X-ray diffraction and DSC-TG, validate the viability of this component-level functional tuning approach. Rapid laser-initiation tests and high-speed photography confirmed that ES-1 undergoes a deflagration-to-detonation transition (DDT) under 980 nm near-infrared laser irradiation, with a delay time of 185 ms. In contrast, ES-2 exhibited excellent moisture resistance but negligible laser sensitivity, whereas ES-3 displayed pronounced hygroscopicity due to an excessive proportion of oxygen-related contacts, which effectively masked its intrinsic laser responsiveness. These results uncover structure-property relationships governed by scaffold and guest regulation, and underscore the critical role of oxygen balance in regulating photoresponsive activity, energy output, and environmental stability. This work provides a practical framework for designing next-generation, environmentally friendly, metal-free laser initiators.