A Bromobenzoyl Pyridine Photosensitizer with Suppressed Phosphorescence for Efficient ROS-Based Photodynamic Therapy.

Organic room-temperature phosphorescent (RTP) and photodynamic therapy (PDT) both rely on triplet excitons generated through intersystem cross-system processes (ISC), but their energy dissipation pathways-the radiative decay of RTP and the reactive oxygen species (ROS) production of photodynamic therapy (PDT) are essentially competitive. Here, we report a photosensitizer based on bromobenzoylpyridine named 2N-Br, which achieves short-lifetime phosphorescence emission (lifetime = 0.018 ms, Φ≈0%), but generates a strong ROS. The molecular structure characterized by carbonyl and bromine atoms can effectively promote the efficient ISC process. Theoretical calculations show that it has a narrow ΔE, while single crystal analysis shows that the dihedral angle (56.03°) and weak intermolecular interaction reduces the restricted molecular movement and enhances the non-radiative transition, which is conducive to the generation of oxygen-dependent ROS. When nanoparticles (2N-Br NPs) were fabricated, this material exhibited a strong PDT effect on 4T1 cells under 405 nm Xe lamp exposure. This work established a molecular strategy that links phosphorescence with the generation of ROS, demonstrating that the generation of strong ROS can coexist with ultra-low phosphorescence efficiency.