Ag(i) emitters with ultrafast spin-flip dynamics for high-efficiency electroluminescence

Abstract

Carbene-metal-amide (CMA) complexes are appealing emitters for organic light-emitting diodes (OLEDs). However, little is known about silver(I)-CMA complexes, particularly electroluminescent ones. Here we report a series of Ag(I)-CMA complexes prepared using benzothiophene-fused carbazole derivatives as amide ligands. These complexes emit via thermally activated delayed fluorescence (TADF), together with high photoluminescence quantum yields of up to 72% in thin films. By strengthening the π-donating ability of the amide ligands, ultrashort emission lifetimes of down to 144 ns in thin films and 11 ns in solution (with a radiative rate constant of ∼10⁷ s⁻¹) are realized, among the shortest lifetimes for TADF emitters. Key to this unique feature is the ultrafast spin-flip dynamics consisting of forward and reverse intersystem crossing rates of up to ∼10⁹ s⁻¹ and ∼10⁸ s⁻¹, respectively, verified by the transient absorption spectroscopic study. The resulting solution-processed OLEDs based on the optimal complex afford record external quantum efficiencies of 16.2% at maximum and 13.4% at 1000 nits, representing the state-of-the-art performance for Ag(I) emitters. This work presents an effective approach for the development of short-lived TADF materials for high-efficiency OLEDs.