Emission and absorption of Ir(ppy)2(CO)(Cl) – temperature dependence, phosphorescence decay dynamics, and assignment of excited states

Emission spectra and decay times of Ir(ppy)2(CO)(Cl) dissolved in THF were recorded for 1.2 K ⩽ T ⩽ 300 K. The emission stems from a triplet state T1 which is split into three substates by less than 1 cm−1. We classify this state as 3LC(ligand centered, ppyππ*) state. At T = 1.2 K, the substates emit independently with three individual decay times (τI = 300 μs, τII = 85 μs, τIII = 9 μs) due to slow equilibration processes, i.e. slow spin-lattice-relaxation, between the substates. With increasing temperature, the emission decay becomes monoexponential as a result of fast equilibration. The results are compared to the spectroscopic behavior of Ir(ppy)3 which represents a metal-to-ligand charge transfer 3MLCT emitter.