Mitochondria-specific imaging and tracking in living cells with two-photon phosphorescent iridium(III) complexes

Two-photon phosphorescent probes have emerged as promising molecular tools for imaging subcellular organelles. Here, the facile synthesis of four new iridium(III)-based mitochondrial probes with two-photon phosphorescence, Ir1-Ir4, is presented. Ir1-Ir4 possess high specificity for mitochondrial localization, which is advantageous in comparison with commercially available mitochondrial trackers of changes in the mitochondrial membrane potential in live cells. In addition to low cytotoxicity and high resistance to photobleaching, Ir1-Ir4 are applicable for imaging and tracking of mitochondrial morphological changes during the early stages of apoptosis. While naturally possessing intensive two-photon properties, Ir1-Ir4 were further developed for imaging of the mitochondria in 3D multicellular spheroids.