Covalently Integrated Polymeric Aza-BODIPY J-Aggregates with NIR-II Absorption for Leakage-Free Photothermal Therapy

J-aggregates of small organic fluorophores offer unique excitonic properties but suffer from inherent instability and dye leakage under physiological conditions; these have limited their biomedical applications. Herein, we report a covalently integrated polymeric aza-BODIPY J-aggregate that overcomes these limitations. An amphiphilic block polymer was synthesized by polymerizing an aza-BODIPY monomer via atom transfer radical polymerization (ATRP) using PEG₁₁₃-Br as the initiator. While the unimolecular polymer conjugate exhibits monomeric absorption at 831 nm, self-assembly into ∼60 nm nanoparticles induce a substantial redshift to 1007 nm, confirming J-aggregate formation. This covalent architecture permanently affixes the chromophores to the polymer backbone, fundamentally eliminating dye leakage. After irradiation with a 1064 nm laser, the obtained micelles exhibited a photothermal conversion efficiency of 49%. Benefiting from their outstanding colloidal stability, these micelles were able to completely eradicate tumors in a mouse model. Consequently, this work establishes a solid and promising platform for the development of J-aggregates with significant bathochromic shifts for photothermal applications in deep tissue.