Phosphine Oxide-Containing Gold(III) Complexes with Tunable Emission Color and Thermally Enhanced Luminescence Behavior

A series of phosphine oxide-containing gold(III) complexes with tunable emission colors spanning from sky-blue to near-infrared region is reported. This is accomplished by the switching of the excited state characters from intraligand to ligand-to-ligand charge transfer through the replacement of the auxiliary ligand from aryl to nitrogen-based ligands. In addition to high photoluminescence quantum yields in both solution and solid-state thin films, these complexes exhibit large radiative decay rate constants of the order of 10⁶ s⁻¹, much larger than those commonly found for other gold(III) complexes. The origin of such enhanced performance is believed to be arising from the occurrence of both thermally activated delayed fluorescence and thermally stimulated delayed phosphorescence processes within the emitters. This is probed by ns- and fs-transient absorption spectroscopy, time-resolved, and temperature-dependent emission spectroscopy. In particular, the direct observation of the upconversion processes and the determination of the activation barriers are achieved in the variable-temperature fs-transient absorption spectroscopic studies. Solution-processed organic light-emitting devices with satisfactory external quantum efficiencies of up to 15.2% are achieved, which could be ascribed to the presence of thermally activated delayed fluorescence and/or thermally stimulated delayed phosphorescence processes. © 2024 The Author(s). Advanced Optical Materials published by Wiley-VCH GmbH.