Molecular Design and\nSynthetic Approaches for the\nRealization of Multichannel Radiative Decay Pathways in Gold(III)\nComplexes and Their Applications in Organic Light-Emitting Devices

A unique class of tridentate diaryltriazine ligand-containing\ngold(III)\ncomplexes with thermally activated delayed fluorescence (TADF) and/or\nthermally stimulated delayed phosphorescence (TSDP) properties has\nbeen designed and synthesized. With a simple structural modification\non the coordination of carbazole moiety in the monodentate ligand,\na large spectral shift of ∼160 nm (ca. 4900 cm<sup>–1</sup>) spanning from sky blue to red emissions has been demonstrated in\nsolid-state thin films. Three-state or four-state models have been\nemployed in fitting the emission lifetimes of the gold(III) complexes\nat various temperatures. The findings clearly indicate the presence\nof three emitting states, S<sub>1</sub>, T<sub>1</sub>, and T<sub>1</sub>′, suggesting the coexistence of TADF, phosphorescence,\nand TSDP. Notably, a minor structural change in the donor moiety between\nphenylcarbazolyl and diphenylaminoaryl has been demonstrated to turn\non/off the TSDP, resulting in TADF-TSDP-phosphorescence or TADF-phosphorescence\nemitters. The TADF and/or TSDP properties have also been supported\nby temperature-dependent ultrafast transient absorption studies, with\nthe direct observation of reverse intersystem crossing (RISC) and\nreverse internal conversion (RIC) and the determination of the activation\nparameters and excited state dynamics. Solution-processed and vacuum-deposited\norganic light-emitting devices (OLEDs) have been prepared, in which\nsky blue emitting devices based on <b>5</b> exhibit an operational\nlifetime LT<sub>70</sub> ∼ 5 times longer than the previously\nreported sky blue emitting analogue that shows only TSDP property.\nThese results have provided valuable insights into the manipulation\nof the excited states via rational molecular design toward the realization\nof gold(III)-based TSDP and/or TADF materials with multiple radiative\ndecay pathways that show enhanced radiative decay rate constants (<i>k</i><sub>r</sub>) for practical OLED applications.