Blue and Near-UV Phosphorescence from Iridium Complexes with Cyclometalated Pyrazolyl or N-Heterocyclic Carbene Ligands

Luminescent Ir(III) complexes have exhibited enormous potential in a range of photonic applications. For example, these Ir complexes can be used as emissive dopants in organic light emitting devices, sensitizers for outer-sphere electron-transfer reactions, photocatalysts for CO2 reduction, photoreductants and singlet oxygen sensitizers, as well as biological labeling reagents. In particular, cyclometalated iridium complexes with emission colors that vary from blue to red have received a great deal of attention recently for their application to light emitting diodes. Since the optical properties and related uses of the cyclometalated Ir complexes are strongly dependent on the characteristics of their ground and lowest excited states, it has become desirable to better understand the interactions between these states and thus determine how to systematically alter the photophysical properties by appropriate ligand or complex design.