Emission properties of Ir(ppy)3 and Ir(ppy)2(CO)(Cl): compounds with different transition types

Walter Josef Finkenzeller; Philipp Stoessel; Marina Kulikova; Hartmut Yersin

doi:10.1117/12.510689

16 February 2004 Emission properties of Ir(ppy)₃ and Ir(ppy)₂(CO)(Cl): compounds with different transition types

Walter Josef Finkenzeller, Philipp Stoessel, Marina Kulikova, Hartmut Yersin

Proceedings Volume 5214, Organic Light-Emitting Materials and Devices VII; (2004) https://doi.org/10.1117/12.510689
Event: Optical Science and Technology, SPIE's 48th Annual Meeting, 2003, San Diego, California, United States

Abstract

Emission properties of Ir(ppy)₃ and of Ir(ppy)₂(CO)(Cl) (ppy^- = 2-phenylpyridinate) are investigated between 1.2K and 300K. Distinct differences are found for the emission spectra, decay behavior, and relaxation dynamics. For both compounds, the emission spectra are broad or only moderately resolved, nevertheless, from time-resolved investigations individual properties of the triplet substates can be deduced. For Ir(ppy)₃, the emission stems from three well separated triplet substates I, II, and III with ΔE_II,I = 13.5 cm^-1 and ΔE_III,I = 83cm^-1. The decay times are τ_I = 145 μs, τ_II = 11 μs, and τ_III = 750 ns. At ambient temperature, all three substates contribute to the emission process, while at 1.5K, the emission results only from substate I. This is due to fast relaxation processes. For Ir(ppy)₂(CO)(Cl), also three substates are identified, but they are only separated by less than 1 cm^-1. Therefore at T = 1.2K, all three substates emit independently with three decay times (τ_I = 330 μs, τ_II = 100 μs, τ_III = 9 μs) due to long spin-lattice relaxation (SLR) times. With increasing temperature to T ≥ 30K and thus growing SLR rates the emission decay becomes monoexponential. In particular, from the amount of splitting (zero-field splitting, ZFS) of the emissive triplet, it is concluded that the emission of Ir(ppy)₃ stems from ³MLCT substates, which result from metal-to-ligand charge transfer (Ir5dppyπ*) states, while Ir(ppy)₂(CO)(Cl) emits from ligand centered triplet substates (³LC) of ppyππ* character. Cyclovoltammetric data are also given and discussed in relation to the spectroscopic data.

Citation Download Citation

Walter Josef Finkenzeller, Philipp Stoessel, Marina Kulikova, and Hartmut Yersin "Emission properties of Ir(ppy)₃ and Ir(ppy)₂(CO)(Cl): compounds with different transition types", Proc. SPIE 5214, Organic Light-Emitting Materials and Devices VII, (16 February 2004); https://doi.org/10.1117/12.510689

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