Ir(III) complexes with great reactive oxygen species (ROS) generation efficiency have attracted attention as a photosensitizer for photodynamic therapy (PDT) because ROS such as singlet oxygen and superoxide radical induce protein inactivation and trigger cancer cell death.¹ However, the Ir(III) complexes produce not enough amount of ROS to kill cancer cells due to low absorption coefficient despite their great ROS generation efficiency. Therefore, high-energy irradiation (>35 J/cm²) is necessary for PDT, which causes normal tissue damage in clinical application.² Herein, we report novel Ir(III) complex, Ir-bxACD, incorporating acedan dye which has strong absorption coefficient, high quantum yield, and great two-photon activation property. As the Ir-bxACD is irradiated, the highly efficient intra-molecular energy transfer (≥98%) occur because the emission energy of acedan dye is well-matched to absorption region of Ir(III) complex. Thereby, the enhanced amount of exciton of Ir-bxACD by energy transfer improves absolute amount of singlet oxygen. As a result, the Ir-bxACD with low-energy irradiation (≤0.3 J/cm²) triggers effective apoptosis on mitochondria of living cancer cells, even with two-photon activation. Consequently, we present rationally designed Ir(III) photosensitizer for PDT incorporating acedan dye, and propose the possibility of PDT using non-invasive irradiation.

1. Nam, J. S.; Kang, M.-G.; Kang, J.; Park, S.-Y.; Kim, H.-T.; Lee, S. J. C.; Seo, J. K.; Kwon, O.-H.; Lim, M. H.; Rhee, H.-W.; Kwon, T.-H. J. Am. Chem. Soc. 2016, 138, 10968.

2. Wu, N.; Cao, J.-J.; Wu, X.-W.; Tan, C.-P.; Ji, L.-N.; Mao, Z.-W. Dalton Trans., 2017, 46, 13482.