BF2‐Bridged Azafulvene Dimer‐Based 1064 nm Laser‐Driven Superior Photothermal Agent for Deep‐Seated Tumor Therapy

Abstract Small organic photothermal agents (PTAs) with absorption bands located in the second near‐infrared (NIR‐II, 1000–1700 nm) window are highly desirable for effectively combating deep‐seated tumors. However, the rarely reported NIR‐II absorbing PTAs still suffer from a low molar extinction coefficient (MEC, ϵ ), inadequate chemostability and photostability, as well as the high light power density required during the therapeutic process. Herein, we developed a series of boron difluoride bridged azafulvene dimer acceptor‐integrated small organic PTAs. The B‐N coordination bonds in the π‐conjugated azafulvene dimer backbone endow it the strong electron‐withdrawing ability, facilitating the vigorous donor‐acceptor‐donor (D‐A‐D) structure PTAs with NIR‐II absorption. Notably, the PTA namely OTTBF shows high MEC (7.21×10 4 M −1 cm −1 ), ultrahigh chemo‐ and photo‐stability. After encapsulated into water‐dispersible nanoparticles, OTTBF NPs can achieve remarkable photothermal conversion effect under 1064 nm irradiation with a light density as low as 0.7 W cm −2 , which is the lowest reported NIR‐II light power used in PTT process as we know. Furthermore, OTTBF NPs have been successfully applied for in vitro and in vivo deep‐seated cancer treatments under 1064 nm laser. This study provides an insight into the future exploration of versatile D‐A‐D structured NIR‐II absorption organic PTAs for biomedical applications.