In vivo imaging tool: High-brightness NIR-II “J-aggregates” based on TICT suppression strategy

The development of high fluorescence quantum yield molecular fluorophores for second-order near-infrared (NIR-II) imaging is highly desirable but remains challenging due to the lack of reliable design guidelines. We report a method to construct “J-aggregates” by combining the inhibition of twisted intramolecular charge transfer (TICT) and electron-withdrawing strategies. Introducing electron-withdrawing substituents at the middle position of the classic boron dipyrromethene (BODIPY) backbone promotes J-type slip stacking, enhancing NIR-II fluorescence through increased electrostatic repulsion and intermolecular hydrogen bonding. The 3,5-aryl position is modified with sulfone and quaternary piperazine groups. The negative inductive effect (–I effect) from strong electron-withdrawing action increases the ionization potential (IP) of the amino group, inhibiting the TICT process and improving the quantum yield to 9.03 % and 16.9 %, respectively. Notably, the fluorescence quantum yield of NBDP-SO 2 increased to 18.2 % after self-assembly with F127, successfully applied in bioimaging. This study provides a new method for constructing high fluorescence quantum yield NIR-II emission by manipulating molecular stacking and establishing the relationship between molecular structure, intermolecular interactions, and fluorescence properties.