Engineering BN‐Doped Open‐Shell Polycyclic Hydrocarbons for Enhanced Photothermal Conversion and Therapy

Traditional inorganic photothermal agents (PTAs) suffer from poor biodegradability, while undoped carbon‐based materials exhibit low photothermal conversion efficiency (PCE). In contrast to the established organic PTAs with donor–acceptor architectures, herein, we developed a new class of atomically precise BN‐doped polycyclic hydrocarbons (PHs) featuring stable diradicaloid ( BN‐Dira : y 0 = 0.74) and tetraradicaloid ( BN‐Tetra : y 0 = 0.43, y 1 = 0.30) character for high‐efficiency photothermal therapy (PTT). Our design is based on the synergistic integration of 1,2‐BN units and radical engineering within an expanded π‐conjugated skeleton. The complementary electron‐donating (N) and electron‐accepting (B) sites effectively modulate the intramolecular charge distribution, which promotes effective electron delocalization. The resulting compounds exhibit exceptional ambient stability, with the tetraradicaloid species demonstrating half‐lives of over 1 year. In addition, the engineered compound BN‐Dira exhibit high NIR absorption and PCE of 83.6%. In vitro, they induce rapid cancer cell apoptosis under NIR irradiation (808 nm). In vivo murine models confirm efficient tumor eradication with minimal side effects. This work establishes a new protocol for stable, radical‐based PH PTAs, providing a solution for high‐performance cancer therapies that can be translated into clinical applications.