The Design, Synthesis And Bioimaging Of Phosphorescent Iridium Complexes Based On Tetrapyrido [3, 2-a:2’,3’-c:3’’,2’’-h:2’’’,3’’’-j] Phenazine(tpphz)

Phosphorescent transition metal complexes(PTMCs) have attracted increasing research interest in biosensing and bioimaging in recent years, owing to their excellent properties including high luminescence efficiency, tunable luminescence colors, significant Stokes shift, high photostability, and long emission lifetime.In this work, iridium(III) complexes Ir1 and Ir2, with phenylpyridine(ppy) as the C^N ligand and tetrapyrido [3, 2-a:2’, 3’-c:3’’, 2’’-h:2’’’, 3’’’-j] phenazine(tpphz) as N^N ligand, were synthesized. Ir1 was a multifunctional phosphorescent probe for both specific nucleus staining of living cells and monitoring intranuclear oxygen level. Ir2 mainly distributed in the cytoplasm. Ir1 exhibited the higher photostability compared with the commercial nuclear dye Hoechst 33342. The mechanism of the cellular uptake of Ir1 was also studied. The results showed that Ir1 internalized into cells through an energy dependent non-endocytotic pathway. With the long emission lifetime of Ir1, the influence of autofluorescence could be eliminated by using the photoluminescence lifetime imaging and time-gated luminescence imaging techniques.Another two iridium(III) complexes Ir3 and Ir4, with 2-(2,4-difluorophenyl)pyridine(F2ppy) as the C^N ligand and tetrapyrido [3, 2-a:2’, 3’-c:3’’, 2’’-h:2’’’, 3’’’-j] phenazine(tpphz) as N^N ligand, were also synthesized. They both stained the cytoplasm and realized two-photon imaging. Compared with the commercial cytoplasm dye CMAC, Ir3 exhibited the higher photostability. With long emission lifetime, the time-gated luminescence imaging technique was used to eliminate the influence of autofluorescence and the intense fluorescence of CMAC. The intracellular oxygen level were also investiguated by using photoluminescence lifetime imaging technique. It supplies a new strategy for detection of hypoxia in tumor.