Organoplatinum(II) J‐Aggregates with Prolonged Triplet Lifetimes for Enhanced Photodynamic and Photocatalytic Therapy

J-aggregates have demonstrated superior phototherapeutic performance compared to their monomeric counterparts. However, the underlying mechanisms for this enhancement are not fully understood. In this work, we report two near-infrared (NIR)-emissive organoplatinum(II) complexes, Pt-2TPE and Pt-2TPA, which self-assemble into J-aggregates via Pt-Pt and π-π stacking interactions. Theoretical calculations reveal that J-aggregates possess lower LUMO energy levels and reduced singlet-triplet energy gaps compared to their monomers, indicating enhanced electron-accepting ability and more efficient intersystem crossing (ISC). Transient absorption spectroscopy confirmed a dramatically prolonged triplet excited-state lifetime in Pt-2TPA J-aggregates (5.8 µs) versus the monomer (123 ns). The efficient oxygen quenching of this long-lived triplet excited-state verified enhanced triplet-state population and sensitization in the J-aggregates. Consequently, the J-aggregates efficiently generate Type I/II reactive oxygen species (ROS) and catalyze NADH oxidation under red light, leading to effective eradication of B16-F10 cells under both normoxic and hypoxic conditions. Furthermore, a biotin-modified nanoformulation (Biotin@Pt-2TPA) exhibits excellent tumor accumulation and tumor growth suppression in vivo. This work provides a strategy to enhance the efficacy of photodynamic and photocatalytic therapy of platinum(II) complexes.