Photophysics, electrochemistry and electrochemiluminescence of water-soluble biscyclometalated iridium (III) complexes

Water soluble cyclometalated iridium(III) complexes with disulfonated bathophenanthroline (DSBP2-) ligand, Ir(L)2DSBPNa (L = 2-phenylpyridine (ppy), 2-phenylbenzothiazole (bt), 1-phenylisoquinoline (piq), and 2,4-difluorophenylpyridine (fppy)), were synthesized and compared with each other electrochemically and spectroscopically in the search for better luminophores potentially useful for the electrochemiluminescence (ECL) based analytical applications. ECL measurement of Ir(L)2DSBPNa in tripropylamine (TPA) containing aqueous buffer solutions led to a conclusion that their high photoluminescence quantum yields (ϕPL) do not necessarily mean high ECL intensities, due presumably to the complexity of the ECL process. Under the experimental conditions, the ECL intensities of Ir(L)2DSBPNa were found to be lower than that of ruthenium(II) trisbipyridine reference. A cyclic voltammetric study has revealed that the oxidative states of some iridium(III) complexes are unstable.