A novel molecular descriptor for highly efficient (ϕTADF > 90%) transition metal TADF Au(iii) complexes†
It is generally perceived that a fast reverse intersystem crossing rate of T1 → S1 (krisc) is crucial for efficient organic thermally activated delayed fluorescence (TADF) emitters. Herein, we demonstrate the non-radiative decay rate of T1 → S0 (kTnr) for transition metal complexes that is even more important. We calculated the interconversion rates among S0, S1 and T1 states for two Au(III)–TADF complexes with triphenylamine (TPA) as a donor moiety but with quite different quantum efficiencies: one with a moderate efficiency of 79% and the other with a high efficiency of 94%, and we found that the former has a much larger krisc (∼1010 s−1) than the latter (∼107 s−1). Such contradictions with the conventional picture are attributed to the relatively large kTnr (∼106 s−1) for the former, leading to an overall lower quantum efficiency. Thus, we propose a novel molecular design descriptor (the triplet non-radiative decay rate kTnr) for highly efficient transition metal TADF emitters. Further, we find that tetradentate ligand scaffolds with 5-5-6 membered chelate rings could reduce kTnr to <105 s−1 for Au(III)–TADF complexes, thereby achieving quantum efficiencies above 90%. Based on this theoretical guideline, we have proposed nine newly designed Au(III) complexes and predicted their high TADF efficiency.
- This article is part of the themed collection: Journal of Materials Chemistry A HOT Papers