Cocrystal engineering: Tuning the charge transfer excitons for highly sensitive luminescent switching materials under multiple stimuli

This paper presents a multi-stimuli responsive cocrystal system with luminescent properties that can be dynamically controlled and demonstrates the responsive mechanism of cocrystals under multiple stimuli (acid/alkali vapor, force, and heat). Detailed spectroscopic, computational, and structural studies exhibit that obvious charge transfer interactions occur in loosely mixed-stacking cocrystals. Such interactions can be weakened by acid vapor fuming due to the strong electron-withdrawing effect of acid cations and strengthened under mechanical grinding. Furthermore, the response time of the cocrystal is in the order of seconds, which is much superior to those of most previously reported stimuli-responsive cocrystals. Accordingly, a high-sensitive fluorescence switching is demonstrated under multiple stimuli, providing an effective strategy to develop smart materials.