Phosphorescent cyclometalated iridium(III) complexes with mono‐, di‐, and tetranuclear as two channel probes to light up the nuclei of living cells

Abstract

By altering the reaction ratio of precursor Ir2(ppy)4Cl2 and bridging ligand of 4,4‐bipyridine (bpy), a series of phosphorescent cyclometalated iridium(III) complexes of mono‐, di‐, and tetranuclear have been successfully obtained and characterized for the first time. The dissociation of bpy ligand can be accelerated by light irradiation or placing these complexes in glutathione (GSH) abundant aqueous solution, bpy releasing rate follows the order Ir1 > Ir2 > Ir3 > Ir4, and with an addition of histidine, a significant blue shift from orange to green phosphorescence was observed. Herein, the cellular dissociation of bpy can be monitored by an orange‐to‐green phosphorescent blue shift, and nuclei of living cells can be lighted up by a set of probes with two phosphorescent channels, and subsequent cellular uptake translocation from cytoplasm to nucleus of Ir complexes could be observed by confocal imaging within 4 h. Besides, the changes of cellular phosphorescence intensity in two fluorescent channels recorded by flow cytometry could reflect different speed of bpy release in human normal and cancer cells. Besides, Ir1–4 exert significant anticancer effect in the dark with low photocytotoxicity, by effectively inducing reactive oxygen species generation, mitochondrial membrane potential depletion, and interacting with biomolecules, and they eventually induce late apoptosis of Hela cell.