Invited paper: Color tuning dopants for electrophosphorescent devices: Toward efficient blue phosphorescence from metal complexes

In this paper, we describe different strategies for achieving efficient blue electro-phosphorescence. The first approach involves the use of ancillary ligand tuning of emission. The emissive unit is an organometallic Ir fragment, whose triplet energy is tuned by the choice of ancillary ligand. This approach is useful for making blue emitters, but luminance efficiency drops when the energy is shifted to saturated blue. The second approach described here is to shift the cyclometallated ligand from phenyl-pyridine to either a phenyl-pyrrazole or phenylimidazole. Both complexes emit strongly in the near UV, however, only the imidazole complex (carbene ligand) emits strongly at room temperature.