Abstract Organic diradicaloids with unique open‐shell structures and properties have been widely used in organic electronics and spintronics. However, their advantageous optical properties have been explored less in the biomedical field. In this work, the photothermal conversion behaviors of a boron‐containing organic diradicaloid (BOD) are reported. BOD can assemble with 1,2‐distearoyl‐sn‐glycero‐3‐phosphoethanolamine‐poly(ethylene glycol) to form rodlike nanoparticles (BOD NPs). These as‐prepared BOD NPs exhibit high photothermal conversion capability and robust photothermal stability. Notably, they possess morphological superiority, which guarantees the effective photothermal therapy of tumors. This work thus demonstrates the promise of organic diradicaloids as efficient photothermal agents for biomedical applications.
