The time-resolved PL decays of all seven complexes were studied by using their corresponding 10 wt%-doped films in PMMA under vacuum. No conclusive PL decay of Cu Mes MIC Naph NPh2, Cu Mes MIC 3,5-CF3Ph NPh2, and Cu Mes MIC 3,5-CF3Ph Cz OMe could be collected due to the poor signal-to-noise ratio, which is consistent with their low PL. On the other hand, the PL decays of Cu Mes MIC Naph Cz, Cu 3,5- MePh MIC Naph Cz, Cu Mes MIC p-An Cz, and Cu Mes MIC Cz showed multiexponential kinetics, with prompt fluorescence lifetimes, p, of 6.1, 5.0, 5.5, and 5.5 ns (Figure -f), respectively, and average delayed emission lifetimes, d, of 12 ms, 4.8 ms, 2.9 ms, and 3.1 s, respectively. The long lifetimes of Cu Mes MIC Naph Cz, Cu 3,5-MePh MIC Naph Cz, and Cu Mes MIC p-An Cz indicate that the emission band at 530 nm is essentially from a triplet excited state. Furthermore, the increasing intensity of the PL emission together with the elongating PL lifetimes with decreasing temperatures for Cu Mes MIC Naph Cz confirms that it emits via phosphorescence (Figure ). In contrast, the much shorter lifetime for Cu Mes MIC Cz indicates that there is a different emission mechanism, which is likely to be TADF.