Pressure-induced discoloration and electronic structural evolution of CL-20/DNB cocrystals

The structural evolution and optical properties of CL-20/DNB cocrystals under high pressure are systematically studied via Raman, florescence, and absorption spectroscopy and Gaussian calculations. Interestingly, the pressure induced a significant change in color from colorless to yellow to red in the CL-20/DNB cocrystal sample. This phenomenon is accompanied by a redshift in the absorption edge, resulting from the enhanced hydrogen bonding interaction and the π‒π stacking effect. Additionally, the photoluminescence (PL) emission clearly increases between 1 atm and 19.5 GPa and quenches later above 20 GPa, which is also caused by the change in the lattice stacking of the cocrystal explosive under high pressure. Moreover, no structural phase transition occurs in the CL-20/DNB cocrystal at pressures ranging from 1 atm to 20 GPa according to the high-pressure Raman spectra, indicating that the cocrystal demonstrates markedly superior structural stability compared with either CL-20 or DNB when considered individual components under high pressure.