Stable π‐Stacked Perylenediimide Radical Dimers for Efficient Photothermal Therapy

Comprehensive Summary Perylenediimide (PDI) radical anions have been extensively investigated and applied in photothermal therapy. However, the current PDI radical anions show poor photothermal conversion efficiency owing to the intrinsic ambient instability and unfavorable aggregation of PDI units, restricting their subsequent practical application. Herein, an N ‐heterocyclic carbene (NHC) metallacycle was employed to fabricate a discrete π‐stacked PDI dimer ( PDI 2 ), which was subsequently reduced to the PDI radical dimer ( PDI 2 ‐RD ) by glutathione (GSH). The well‐defined dimer packing endows PDI 2 ‐RD with robust ambient stability over 30 days, suppresses the quenching of PDI radical anions, and facilitates intramolecular electron transfer. As a result, the PDI 2 ‐RD achieves a photothermal conversion efficiency of 84.9%, which is 13.1 times higher than that of the monomeric PDI radical anion under 808 nm laser irradiation. For in vitro and in vivo experiments, the GSH‐induced PDI 2 ‐RD within tumor cells showed excellent photothermal therapeutic efficacy as well as good biocompatibility. This study presents an alternative strategy to develop stable and discrete radical dimers for efficient photothermal therapy.