The origin of the increased photodegradation of fac-Ir(ppy)3 compared to Ir(pmi)3 may be due to the relatively lower-lying non-emissive metal-centred 3 MC excited states in fac-Ir(ppy)3 that becomes populated upon photoexcitation. Population of these non-emissive 3 MC states leads to structural degradation through thermal decay processes. Between the two isomers, the increased stability of fac-vs.