A Comprehensive Survey of Cationic Iridium(III) Complexes Bearing Nontraditional Ligand Chelation Motifs

The useful optoelectronic properties of cationic iridium(III) complexes have been exploited in diverse applications, from visual displays to biological probes to analytical sensors. It is thus not surprising to note the increased recent efforts to document, understand, and ultimately control the photophysical and electrochemical properties of the archetypal cationic iridium(III) complex [(ppy)2Ir(bpy)]+, in which ppyH = 2-phenylpyridine and bpy = 2,2′-bipyridine, and decorated versions thereof. Of the ligand architectures explored, the greatest attention has been devoted to ligands that incorporate the common pyridine unit. In this Microreview, we survey the salient emission and electrochemical properties of cationic iridium(III) complexes of the form [(C∧N)2Ir(L∧X)]+, in which C∧N is a cyclometalating ligand and L∧X is a bidentate neutral ancillary ligand, with at least one heterocyclic ligand other than pyridine. We contrast their properties to that of [(ppy)2Ir(bpy)]+ and highlight recent exploits in materials applications.