Realizing Aggregation-Induced Emission Improvement and Multistimulus-Responsive Reversible Fluorescence Switching through Multicomponent Crystals

Abstract

Modulating the luminescent characteristics of solid materials via the multicomponent crystallization process to form cocrystals and hydrates poses a formidable and significant challenge. In this study, we demonstrated the aggregation-induced emission characteristics of piroxicam and synthesized four distinct cocrystals using salicylic acid, m-chlorobenzoic acid, saccharin, and 1-hydroxy-2-naphthalenecarboxylic acid as coformers. We comprehensively characterized the crystal structures and luminescent properties of these cocrystals using powder X-ray diffractometer, fluorescence microscopy, and fluorescence spectrophotometry. Moreover, the relationship between the crystal structure and fluorescence properties was established through theoretical analyses, including the calculation of intermolecular interactions, the distribution of frontier orbitals obtained based on density functional theory, and the electron density distribution derived from molecular electrostatic potential calculations. Additionally, we synthesized a novel piroxicam hydrate that exhibits a reversible fluorescence switching effect in response to acidic, basic, and thermal stimuli upon absorbing, eliminating, or replacing water molecules within the lattice, which renders it suitable for application in thermal and pH sensors, as well as information encryption. Overall, this approach offers a promising framework for precisely tuning the fluorescent properties of AIE molecules through the hydration and dehydration processes of organic crystals.