Quantitative Evaluation of Mechanochromic Luminescent Materials under Controlled Grinding Stimuli

Mechanochromic luminescent (MCL) materials have attracted growing attention owing to their potential applications in sensing, display, and security technologies. Although crystalline MCL materials have been the most intensively investigated, quantitative evaluation of their mechanical-stimuli-responsiveness remains challenging, particularly in powdered form. Herein, a custom-built apparatus is developed to monitor real-time emission color changes in crystalline powders of MCL materials under quantitatively controlled grinding stimuli. Time-dependent emission spectra obtained using this apparatus are analyzed using two newly defined parameters kprog and kconv. These parameters allow for quantitative comparison of the mechanical-stimuli-responsiveness of a series of organic and organometallic MCL materials with diverse structures and provide insights into their underlying mechanisms. Load-dependent measurements further suggest that mechanical force lowers the activation barrier for the collapse of the crystal structure. This methodology offers a general strategy for evaluating powdered MCL materials and contributes to the rational design and development of advanced MCL systems.