Heteronuclear phosphorescent iridium(III) complexes with tunable photophysical and excited-state properties by chelating BF₂ moiety for application in bioimaging

In the present study, we explored a novel design strategy of heteronuclear phosphorescent iridium(iii) complexes chelated by BF₂ moiety with 3-hydroxypicolinic acid as the chelate ligand and synthesized a new series of iridium(iii) complexes [Ir(dfppy)₂(hpa)BF₂] (1b), [Ir(ppy)₂(hpa)BF₂] (2b) and [Ir(tpq)₂(hpa) BF₂] (3b) (hpa = 3-hydroxypicolinic acid, dfppy = 2-(2,4-difluorophenyl)pyridine, ppy = 2-phenylpyridine, tpq = 2-(thiophen-2-yl)quinoline) under mild conditions. The emission colors and wavelengths of iridium(iii) complexes can be affected evidently by chelating BF₂ moiety into iridium(iii) complexes, and this effect will be changed with the difference of cyclometalating C∧N ligands. A combination of UV-vis absorption, photoluminescence, excited-state lifetime measurements and theoretical calculations has provided the significant insight into the nature of the excited state and photophysical properties of these interesting iridium(iii) complexes. Moreover, the exclusive staining of cytoplasm and low cytotoxicity were demonstrated for these new iridium(iii) complexes, which made them promising candidates as multi-color phosphorescent dyes for living cell imaging.