TADF-Type Organic Afterglow Nanoparticles with Temperature and Oxygen Dual-Responsive Property for Bimodal Sensing

Stimuli-responsive organic afterglow materials, which feature long-lived excited states compared to their fluorescence counterparts, have been shown to exhibit distinct advantages to work normally even in the presence of a strong fluorescence background. However, most stimuli-responsive afterglow materials only function in the solid state, with those in the aqueous environment being rarely explored. Besides, most responsive afterglow systems can only respond to single stimulus. Here, we report the fabrication of thermally activated delayed fluorescence (TADF)-type organic afterglow nanoparticles with temperature and oxygen dual-responsive property in an aqueous environment. Experimental and computational studies reveal that the key to realize the dual responsiveness is the TADF mechanism. The k (RISC)/k (P) ratio determines the TADF/phosphorescence intensity ratio and consequently afterglow color, where k (RISC) and k (P) represent the reverse intersystem crossing rate and phosphorescence rate, respectively. The dark triplets of TADF-type afterglow nanoparticles are sensitive to oxygen, whose intensity and lifetime would increase in the hypoxia condition. Since the afterglow color and TADF intensity (or lifetime) can be monitored at different channels for potential multiplexed sensing, the temperature and oxygen dual-responsive afterglow nanoparticles would display promising application in the biomedical area.