Phosphorescent iridium(III) complexes as multicolor probes for specific mitochondrial imaging and tracking

In the present study, four phosphorescent iridium(III) complexes [Ir(C–N)2(PhenSe)]+ (Ir1–Ir4, in which C–N = 2-(2,4-difluorophenyl)pyridine (dfppy), dibenzo[f,h]quinoxaline (dbq), 2-phenylquinoline (2-pq) and 2-phenylpyridine (ppy), PhenSe = 1,10-phenanthrolineselenazole) with tunable emission colors were developed to image mitochondria and track the dynamics of the mitochondrial morphology. In comparison with commercially available mitochondrial trackers, Ir1–Ir4 possess high specificity to mitochondria in live and fixed cells without requiring prior membrane permeabilization or the replacement of the culture medium. Due to the high resistance of Ir1–Ir4 to the loss of mitochondrial membrane potential as well as the appreciable tolerance to environmental changes, these complexes are applicable for the imaging and tracking of the mitochondrial morphological changes over long periods of time. In addition, Ir2–Ir4 exhibited superior photostability compared to the commercially available mitochondrial trackers. These colorful iridium(III) complexes may contribute to the future development of staining agents for organelle-selective imaging in living cells.