Frontiers in photodynamic therapy: type I NIR-II photosensitizers with aggregation-induced emission features

Photodynamic therapy (PDT) is a minimally invasive treatment modality characterized by high spatiotemporal precision and controllability, showcasing extensive potential applications in the biomedical field in recent years. However, conventional type II photosensitizers, which rely heavily on oxygen availability, exhibit limited therapeutic efficacy in hypoxic microenvironments such as solid tumors. Type I photosensitizers with their superior hypoxia tolerance offer an effective solution to this challenge. In particular, aggregation-induced emission (AIE)-active type I photosensitizers, especially those operating in the second near-infrared window (NIR-II, 1000-1700 nm), have attracted extensive research interest due to their unique advantages, including enhanced fluorescence emission in the aggregated state, efficient generation of free radical reactive oxygen species (ROS), and excellent tissue penetration capability. This review systematically discusses molecular design strategies for NIR-II AIE photosensitizers, focusing on enhancing intersystem crossing (ISC) and introducing high electron-affinity groups to promote the type I photodynamic process. Furthermore, it comprehensively summarizes the potential applications of these materials in tumor therapy, antibacterial treatment, and antiviral therapy, providing new perspectives for addressing the limitations of conventional PDT and advancing precision treatment strategies.