Fe3+ Oxidation Strategy Enhances the Nonradiative Transition Ability of a Near‐Infrared BODIPY Photosensitizer for Photothermal Therapy

Abstract Near‐infrared (NIR) BODIPY‐based photosensitizer NIR‐2BDP is constructed through an Fe 3+ oxidation strategy. Theoretical calculations and experimental results show that intramolecular charge separation effectively reduces the HOMO‐LUMO energy gap, broadens the light absorption range, and suppresses radiative transition (RT) processes. The decrease in the singlet‐triplet energy gap enhances the intersystem crossing (ISC) ability of NIR‐2BDP (the spin‐orbit coupling constant (S 1 →T 1 ) is 2.5 times that of NIR‐BDP , and the singlet oxygen ( 1 O 2 ) quantum yield is 2.1 times that of NIR‐BDP ). The low RT (only 2.2% fluorescence quantum yield) and relatively low triplet generation (11.7% 1 O 2 quantum yield) suggest that NIR‐2BDP should have a stronger contribution of nonradiative transition (NRT) processes (and hence a higher photothermal conversion capability). Nanoparticles constructed from NIR‐2BDP and DSPE‐mPEG 2000 exhibit good photothermal conversion efficiency (41.4%) and killing efficiency to tumor cells in the NIR‐II window (1000‐1700 nm). Therefore, this study extends the sensitization window and improves the NRT ability, paving the way for the construction of multi‐functional NIR BODIPY‐like photosensitizers.