Stable π‐Radical Materials as Emerging and Excellent Phototheranostic Agents

Comprehensive Summary Stable organic π‐radicals, featuring open‐shell electronic configurations with unpaired electrons delocalized over extended conjugated frameworks, exhibit intriguing optoelectronic and magnetic properties, including spin‐dependent electronic structures, narrow band gaps, and multiple redox states. While these attributes have spurred their use in photoelectronic and spintronic devices, their potential in biomedical theranostics remains largely untapped. Phototheranostics, which exploits light‐triggered excited‐state energy conversion for simultaneous diagnosis and therapy, offers high spatiotemporal precision and minimal side effects. The unique excited‐state dynamics of π‐radicals, such as doublet emission, enhanced photothermal conversion and redox‐active behavior that facilitates Type‐I photosensitization, position them as promising next‐generation phototheranostic agents. This review systematically summarizes recent progress on π‐radical‐based platforms for fluorescence imaging, photoacoustic imaging, photothermal therapy, photodynamic therapy and photo‐immunotherapy. Moreover, the remaining challenges and emerging prospects in the phototheranostic application of these materials are critically examined, shedding light on their potential to facilitate future technological advances.