Organic Activatable Afterglow Imaging Probes: From Molecular Design to Biomedical Translation

Organic activatable afterglow probes have developed into a distinct class of optical imaging tools. They allow for a temporal separation between signal emission and external irradiation, thereby enabling high-contrast imaging. We have summarized the latest advances in the design of organic activated afterglow probes, with a particular focus on their excitation mechanisms, performance modulation, and activation strategies, including energy transfer, intramolecular regulation, and singlet oxygen(¹O₂)-mediated processes. The roles of various external energy sources, including light, ultrasound, and X-rays, in inducing afterglow emission are also discussed. We further highlight representative probe designs for detecting bioactive small molecules, enzymes, and microenvironment signals, and explore how these systems translate molecular activation events into afterglow signals. This review emphasizes biomedical applications, particularly tumor-related imaging, visualization of immune cell dynamics, and disease-related imaging of the liver and cardiovascular system. The role of these activated afterglow probes in surgical navigation and treatment monitoring is elucidated. The discussion also addresses remaining challenges in this field, including how to modulate probe performance, improve selectivity in complex biological environments, and enhance deep tissue imaging capabilities while ensuring translational safety.