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

Abstract

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 T 1 which is split into three substates by less than 1 cm −1. We classify this state as 3 LC(ligand centered, ppyππ*) state. At T = 1.2 K, the substates emit independently with three individual decay times ( τ I = 300 μs, τ II = 85 μs, τ III = 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 3 MLCT emitter.