Among the most promising phosphorescent blue emitters are iridium(III) complexes with cyclometallating N-heterocyclic carbene (NHC) ligands. In these complexes the strongly σ-donating and weakly p-accepting NHC contributes to greatly destabilize the LUMO of the Ir(C^C)3 complex and thus increase the energy of the emissive triplet state. Luminescent Ir(C^C)3 complexes were first reported by Thompson and co-workers in 2005; 4, 10 however, in these early examples [fac-Ir(pmi)3 and fac-Ir(pmb)3] the photoluminescence quantum yields, FPL, were very low, and the complexes emitted in the near UV. A step-change in the photophysical properties of Ir(C^C)3 complex occurred in 2016 where Thompson, Forrest and co-workers reported a bright, blue complex, mer-Ir(pmp)3, (λPL = 465 nm, ΦPL = 78% in degassed 2-MeTHF) and the OLEDs showed unprecedentedly high maximum external quantum efficiencies (EQEmax = 14.4%) and blue electroluminescence [CIE = (0.16, 0.15)],