Tuning the Cellular Uptake Properties of Luminescent Heterobimetallic Iridium(III)-Ruthenium(II) DNA Imaging Probes

The synthesis of two new luminescent dinuclear IrIII-Ru-II complexes containing tetrapyrido[3,2-a: 2',3'-c:3''',2 '''-h: 2 '''',3 ''''-j] phenazine (tpphz) as the bridging ligand is reported. Unlike many other complexes incorporating cyclometalated Ir-III moieties, these complexes display good water solubility, allowing the first cell-based study on Ir-III-Ru-II bioprobes to be carried out. Photophysical studies indicate that emission from each complex is from a Ru-II excited state and both complexes display significant in vitro DNA-binding affinities. Cellular studies show that each complex is rapidly internalised by HeLa cells, in which they function as luminescent nuclear DNA-imaging agents for confocal microscopy. Furthermore, the uptake and nuclear targeting properties of the complex incorporating cyclometalating 2-(4-fluorophenyl)-pyridine ligands around its Ir-III centre is enhanced in comparison to the non-fluorinated analogue, indicating that fluorination may provide a route to promote cell uptake of transition-metal bioprobes.