Naphthalimide Nanoprobe with Enhanced Electron-Withdrawing Ability and Large Stokes Shift for NIR-II Fluorescence Imaging-Guided Phototheranostics

Nanoprobes with NIR-II fluorescence and a large Stokes shift are highly desirable for high-quality bioimaging applications. However, designing NIR-II fluorescent nanoprobes with the desired photophysical properties based on small organic molecules remains a significant challenge. Herein, we report a naphthalimide (NMI)-based NIR-II fluorescent molecule, NMI-BF₂, by further enhancing the electron affinity of NMI through the incorporation of boron difluoride formazanate. NMI-BF₂ exhibits a sufficient NIR-II quantum yield (QY) of 0.53%, a large Stokes shift of 263 nm, and excellent photostability. For biological applications, NMI-BF₂ is coassembled with fetal bovine serum (FBS) to prepare a biocompatible nanoprobe, NMI-BF₂/FBS, which maintains a good NIR-II QY of 0.21% and a photothermal conversion efficiency of 32.5%. In vitro and in vivo studies verified that the NMI-BF₂/FBS nanoprobe shows an excellent photothermal antitumor therapeutic effect, guided by NIR-II fluorescence and photoacoustic imaging.