To compare the rate constants of our new complexes with the published examples, we prepared complex 3 that has the same auxiliary ligand, cyclometallated 2-(2,4-difluorophenyl)-pyridine (Figure ). In addition to complex 3, we also prepared complex 4 employing cyclometallating 2phenylquinoline to achieve more red-shifted absorption and emission spectra that are desirable in luminescent bioimaging due to the improve penetrability of longer wavelength light. The ligand 7 was synthesised in one step by the condensation of 1,10-phenanthroline-5,6-dione with in-situ generated formamidrazone. The complexes 3 and 4 are then derived by the reaction with the corresponding dichloro-bridged intermediates based on well-known chemistries. The complexes were isolated as chloride salts rather than more traditional, but less water-soluble, hexafluorophosphate analogues. The details of the synthesis and all analytical data can be found in supplementary information.