Three-photon absorption iridium() photosensitizers featuring aggregation induced emission

In this study, three-photon absorbing cyclometalated iridium( iii ) complexes ( Ir-H , Ir-8C , and Ir-O ) were rationally designed and synthesized through fine-tuning of an auxiliary ligand. The long alkoxy chains in Ir-8C and Ir-O allow maintaining the intramolecular mobility upon aggregation, resulting in the absence of emission in aggregated states. In comparison with Ir-8C and Ir-O , Ir-H exhibited excellent aggregation-induced emission properties in dimethyl sulfoxide/water (DMSO/H 2 O) solution. The three-photon absorption cross section reached 300 × 10 −92 cm 6 s 2 photon −2 in the aggregated state. Furthermore, the singlet oxygen ( 1 O 2 ) quantum yield of Ir-H could be increased to 0.87 through the synergistic effect of the strong spin-orbit coupling effect of the iridium center and the aggregation-induced intersystem crossing. Ir-H effectively induced cancer cell death both ex vivo and in vivo , with potential application in multiphoton imaging-guided photodynamic therapy. Ir-H exhibits better three-photon absorption aggregation induced emission property, and thus can enhance the photodynamic therapy efficiency.