A detracting feature of many phosphorescent iridium complexes is the presence of thermally accessible 3 MC excited states. Their population leads to increased non-radiative decay and degradation of the complex induced by the lengthening of the Ir-ligand bonds resulting in deligation. The strongly coordinating and s-donating NHC ligands in Ir(C^C)3 complexes possess a much larger octahedral splitting gap, destabilizing the 3 MC state and increasing energy required to access this state. Secondly, while the 3 MC excited state nonetheless remains thermally accessible, the lengthening of the Ir-C bond that results from the population of this state is reversible and does not lead to cleavage of the Ir-C bond, as seen for Ir-N bonds such as those in functionalized 2-phenylpyridine type ligands; indeed, the stability of Ir(C^C)3 complexes has been demonstrated, with the homoleptic carbene complex fac-Ir(tpz)3 stable under irradiation in thin films doped with both fac-Ir(tpz)3 and a strongly chelating diimine ligand, this is in contrast to films containing fac-Ir(ppy)3 (ppy = 2phenylpyridinato), which showed ligand dissociation under the same conditions. Tuning the emission colour of iridium complexes containing ppy-type ligands through judicious substitution of electron-donating and withdrawing groups is a well-documented strategy, with emission colour readily tuned from sky-blue to red. The use of strongly σdonating NHC ligands results in a destabilised LUMO (relative to ppy-type ligands) and blueshifted emission. The tuning of the emission colour of Ir(C^C)3 complexes is now well understood, where modification of the NHC imidazole with annelated electron-deficient heterocycles can result in a red-shifted emission, as exemplified in fac-Ir(tpz)3 (λPL = 480 nm in 2-MeTHF). Decoration of the phenyl ring with electron-withdrawing or donating groups results in a blue or red shift, respectively, illustrated by the comparison of mer-Ir(CF3pbp) 3 and the related mer-Ir(tbpbp)3, an analogous complex that has a t Bu group replacing the electron withdrawing CF3 group, with λPL = 420 nm and 480 nm in DCM, respectively. Ir(C^C)3 complexes can exhibit very high ΦPL, with many complexes having ΦPL > 70%. The emission lifetime of most Ir(C^C)3 complexes are fairly short, with τPL < 1.5 μs. Complexes with a T1 of strongly LC character, such as mer-Ir(tfp_tz)3, have a longer emission lifetime, in this case τPL = 4.75 μs.