Au(I)‐TADF Emitters for High Efficiency Full‐Color Vacuum‐Deposited OLEDs and TADF‐Sensitized Fluorescent OLEDs with Ultrahigh Brightness and Prolonged Operational Lifetime

Abstract

<p>Herein a class of structurally simple and operationally stable Au(I)-TADF (TADF = thermally activated delayed fluorescence) materials, based on a carbene–metal–amide (CMA) molecular scaffold comprised of sterically bulky <em>N</em>-heterocyclic carbene ligands with <em>N</em>-heterocyclic <em>π</em>-annulation, are reported. These CMA(Au) emitters are thermally stable, adopt coplanar or orthogonal geometry between the carbene and amide ligands, and show strong blue to deep red TADF emissions (466–666 nm) from thermally equilibrated singlet ligand-to-ligand-charge-transfer excited states with emission quantum yields of 0.63–0.99 and radiative decay rate constants of 0.68–3.2 × 10⁶ s⁻¹ in thin film samples at room temperature. The effects of increasing <em>π</em>-extension and orthogonal molecular geometry are similarly manifested in the reduction of both singlet–triplet energy gap and S₁ transition dipole moment. The vacuum-deposited Au(I) organic light-emitting diodes (OLEDs) display superior electroluminescence characterized by ultrahigh brightness up to 300 000 cd m⁻² and external quantum efficiencies (EQEs) up to 26.2% with roll-offs down to 2.6% at 1000 cd m⁻² alongside record-setting device lifetimes (LT₉₅) up to 2082 h. Ultrapure-green TADF-sensitized fluorescent OLEDs employing the CMA(Au) emitter as sensitizer and a multiresonance terminal emitter achieve EQEs of up to 25.3%.<br></p>