A Spiro‐Based NIR‐II Photosensitizer with Efficient ROS Generation and Thermal Conversion Performances for Imaging‐Guided Tumor Theranostics

Abstract Organic photosensitizers (PSs) possessing NIR‐II emission and photodynamic/photothermal effect have received a great sense of attention for their cutting‐edge applications in imaging‐guided multimodal phototherapy. However, it is highly challenging to design efficient PSs with high luminescence and phototherapy performance simultaneously. In this study, a spiro‐functionalization strategy is proposed to alleviate aggregate‐caused quenching of PSs and promote photodynamic therapy, and the strategy is verified via a spiro[fluorine‐9,9ʹ‐xanthene]‐modified NIR‐II PS (named SFX‐IC) with an acceptor–donor–acceptor configuration. SFX‐IC‐based nanoparticles (NPs) display a high molar extinction coefficient of 7.05 × 10 4 m ‒1 cm −1 at 645 nm due to strong intramolecular charge‐transfer characteristics. As expected, the as‐prepared NPs show strong NIR‐II emission with a fluorescence quantum yield of 1.1%, thanks to the spiro‐configuration that suppressing excessively intermolecular π–π stacking. Furthermore, SFX‐IC NPs not only efficiently generate 1 O 2 and O ∙− 2 under 660 nm laser irradiation, but also possess good photothermal effect with photothermal conversion efficiency of 47.14%. Consequently, SFX‐IC NPs can be served as versatile phototheranostic agents for NIR‐II fluorescence/photoacoustic imaging‐guided phototherapy, manifesting that the spiro‐functionalized strategy is a powerful tool to construct efficient NIR‐II emitting PSs.