The Effect of the Ancillary Ligand on Optical and Redox Properties of Cyclometalated Iridium(III) 2,5-Diphenyloxazole Complexes

Abstract—Two series of bis-2,5-diphenyloxazolato cyclometalated iridium(III) complexes with substituted 2,2′-bipyridine or dipyridophenazine as the ancillary ligand have been prepared and characterized by X-ray structural analysis, ¹H NMR, and high resolution mass spectrometry. Bipyridine-based complexes exhibited bright emission in the yellow-orange region in solution, whereas their dipyridophenazine analogues demonstrated low quantum yields in the same spectral area. Varying the substituents in the ancillary ligand (CH₃, H, COOH) caused noticeable shifts of the long-wavelength absorption bands retaining the redox potentials of the complexes practically unchanged. Crystallization of the complexes with iodine species gave interesting salts containing infinite polyiodide chains forming intermolecular contacts with the π-system of the ligands. Complexes bearing “anchoring” COOH-groups were used in sensitization of titania photoanodes followed by their study under the AM 1.5 G condition.