Thienylquinoline-based ionic Iridium(III) complexes as highly efficient Sonosensitizers for Sonodynamic therapy

Sonodynamic therapy (SDT) is an emerging cancer therapeutic method whose mechanism is very similar to that of photodynamic therapy (PDT), with the primary difference being that its excitation source is ultrasound. Hence, SDT has significantly a greater penetration depth, making it more suitable for treating deep-seated tumors. Sonosensitizers, as a key component of SDT, can be excited by ultrasound and generate reactive oxygen species (ROS). In this work, two novel ionic iridium(III) complexes (Ir1 and Ir2) bearing a 4-methyl-2-(thiophen-2-yl)quinolone cyclometalating ligand are synthesized, and their photophysical properties, sono-chemical properties and in vitro SDT are studied. Ir1 and Ir2 have long excited-state lifetimes and exhibit good stability under ultrasound and at different pH values. These two iridium(III) complexes can generate singlet oxygen under ultrasound both in solution and in cells. They show good biocompatibility in the absence of ultrasound and high toxicity in the presence of ultrasound, indicating their great potential for sonodynamic therapy applications.