Quaternary Ammonium Salt Based NIR‐II Probes for In Vivo Imaging

Traditional luminescent materials including fluorescent probes suffer from notorious aggregation-caused quenching (ACQ) in aqueous solutions. Although several approaches such as the aggregation-induced emission (AIE) effect have been developed, it remains a significant challenge to identify an effective and efficient strategy to resolve this issue. Herein, quaternary ammonium salts Q8PBn and Q8PNap as a novel class of bright near infrared window II (NIR-II, 1,000 - 1,700 nm) probes were designed and synthesized, and the twisted intramolecular charge transfer (TICT) formation at the excited state can be effectively suppressed for the newly designed probes. Furthermore, Q8PNap complexation with fetal bovine serum (Q8PNap/FBS) significantly increased the quantum yield by ~ 32-fold compared with PEGylated tertiary amine Q8P, and Q8PNap/FBS was successfully used to achieve high spatial and temporal resolution imaging of hind limb vasculature, lymphatic system, and small tumor metastasis, as well as precise NIR-II imaging-guided tumor and lymph node surgery in small animal models for the first time.