Efficient emission from exciplexes utilizing bidentate C^N ligand-containing bis(aryl)gold(iii) complexes as the acceptor components

Abstract

Exciplex emitters are promising candidates for the fabrication of efficient organic light-emitting diodes (OLEDs). Current research on the constituent molecules of exciplexes, particularly the acceptor components, has primarily focused on purely organic molecules, which limits their development. This study presents the design and synthesis of three new bidentate gold(III) complexes featuring two electron-deficient monodentate aryl ligands, which serve as effective acceptors for exciplex formation with the organic donor 4,4′-cyclohexylidenebis[N,N-bis(p-tolyl)aniline] (TAPC). The resulting exciplexes demonstrate high photoluminescence quantum yields (Φ) of up to 68% and short emission decay times ranging from 2.18 to 4.11 μs, indicating efficient light emission. Comprehensive experimental and theoretical analysis elucidates the roles of energy level alignment, spin–orbit coupling (SOC), and reorganization energy in modulating excited-state properties of these optical functional complexes. Temperature-dependent measurements show that the emission dynamics transition from phosphorescence at lower temperatures to TADF at room temperature, highlighting the tunable properties of the mixed films containing the gold(III) acceptors. Despite previous focus on tridentate and tetradentate gold(III) complexes, this work highlights the underexplored potential of bidentate analogs, providing insights into their structure–property relationships and their suitability as exciplex acceptors. A solution processed OLED device utilizing the PPyAuPhCN:TAPC exciplex as the emission layer achieved a maximum external quantum efficiency (EQE) of 8.2%, demonstrating its potential practicality in optoelectronic devices. This work not only advances the understanding of bidentate gold(III) complexes in exciplex systems but also provides a strategic framework for developing efficient luminescent materials using engineered metal complexes.