Boosting O2•− Photogeneration via Promoting Intersystem‐Crossing and Electron‐Donating Efficiency of Aza‐BODIPY‐Based Nanoplatforms for Hypoxic‐Tumor Photodynamic Therapy

Abstract Tumor hypoxia severely impedes the therapeutic efficacy of type II photodynamic therapy (PDT) depending on singlet oxygen ( 1 O 2 ) generation. To combat hypoxic tumors, herein, a new approach is devised to boost superoxide radical (O 2 •− ) photogeneration for type I PDT. Heavy atoms are introduced onto aza‐BODIPY molecules (iodine substituted butoxy‐aza‐BODIPY, IBAB) to promote their intersystem‐crossing (ISC) ability. Meanwhile, methoxy‐poly(ethylene glycol)‐ b ‐poly(2‐(diisopropylamino) ethyl methacrylate) (mPEG‐PPDA) with enhanced electron‐donating efficiency is employed as a coating matrix to encapsulate IBAB, thereby obtaining amphiphilic aza‐BODIPY nanoplatforms (PPIAB NPs). Under irradiation, triplet‐state IBAB in PPIAB NPs is efficiently generated from singlet state favored by the elevated ISC ability. The electron‐rich environment provided by mPEG‐PPDA can donate triplet‐state IBAB with one electron to form charge‐separated‐state IBAB, which in turn transfers electron to O 2 for O 2 •− production. Significantly, owing to recyclable O 2 generated by disproportionation or Harber–Weiss/Fenton reaction, prominent O 2 •− is generated by PPIAB NPs even in a severe hypoxic environment (2% O 2 ), enabling superior therapeutic efficacy (96.2% tumor‐inhibition rate) over NPs not following this strategy. Thus, the proof‐of‐concept design of ISC‐enhanced and electron‐rich polymer encapsulating PPIAB NPs illuminates the path to preparing O 2 •− photogenerator for hypoxic cancer treatment.