Cyclometalated Iridium(III) Complexes as High-Sensitivity Two-Photon Excited Mitochondria Dyes and Near-Infrared Photodynamic Therapy Agents.

Photodynamic therapy (PDT) using two-photon near-infrared light excitation is a very effective way to avoid the use of short-wavelength ultraviolet or visible light which cannot efficiently penetrate into the biological tissues and is harmful to the healthy cells. Herein, a series of cyclometalated Ir(III) complexes with a structurally simple diimine ligand were designed and the synthetic route and preparation procedure were optimized, so that the complexes could be obtained in apparently higher yield, productivity, and efficiency in comparison to the traditional methods. Their ground state and excited singlet and triplet state properties were studied by spectroscopy and quantum chemistry theoretical calculations to investigate the effect of substituent groups on the photophysical properties of the complexes. The Ir(III) complexes, especially Ir1 and Ir3, showed very low dark toxicities and high phototoxicities under both one-photon and two-photon excitation, indicating their great potential as PDT agents. They were also found to be highly sensitive two-photon mitochondria dyes.