Real-time tracking mitochondrial dynamic remodeling with two-photon phosphorescent iridium (III) complexes

Mitochondrial fission and fusion control the shape, size, number, and function of mitochondria in the cells of organisms from yeast to mammals. The disruption of mitochondrial fission and fusion is involved in severe human diseases such as Parkinson's disease, Alzheimer's disease, metabolic diseases, and cancers. Agents that can real-time track the mitochondrial dynamics are of great importance. However, the short excitation wavelengths and rapidly photo-bleaching properties of commercial mitochondrial dyes render them unsuitable for tracking mitochondrial dynamics. Thus, mitochondrial targeting agents that exhibit superior photo-stability under continual light irradiation, deep tissue penetration and at intrinsically high three-dimensional resolutions are urgently needed. Two-photon-excited compounds employ low-energy near-infrared light and have emerged as a non-invasive tool for real-time cell imaging. Here, cyclometalated Ir(III) complexes (Ir1-Ir5) are demonstrated as one- and two-photon phosphorescent probes for the real-time imaging and tracking of mitochondrial fission and fusion. The results indicate that Ir2 is well suited for two-photon phosphorescent tracking of mitochondrial fission and fusion in living cells and in Caenorhabditis elegans (C. elegans). This study provides a practical use for mitochondrial targeting two-photon phosphorescent Ir(III) complexes.