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 on silver(I)-CMA complexes, particularly electroluminescent ones. Herein, we report a series of Ag(I)-CMA complexes 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 film and 11 ns (with a radiative rate constant of ~10⁷ s⁻¹) in solution are realized, among the shortest lifetimes for TADF emitters. The 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 transient absorption spectroscopic study. The respective solution-processed OLEDs based on the optimal complex afford record external quantum efficiencies of 16.2% at a 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.