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 less than or equal to T less than or equal to 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 (LC)-L-3(ligand centered, ppypipi*) state. At T = 1.2 K, the substates emit independently with three individual decay times (tau(I) = 300 mus, tau(II) = 85 mus, tau(III) = 9 mus) 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 (MLCT)-M-3 emitter. (C) 2004 Elsevier B.V. All rights reserved.