Motivation on Intramolecular Through-Space Charge Transfer for the Realization of Thermally Activated Delayed Fluorescence (TADF)–Thermally Stimulated Delayed Phosphorescence (TSDP) in C^C^N Gold(III) Complexes and Their Applications in Organic Light-Emitting Devices

Abstract

Thermally activated delayed fluorescence (TADF) and the very recently established thermally stimulated delayed phosphorescence (TSDP) are two promising approaches for enhancing the performance of organic light-emitting devices (OLEDs). Here, we have developed a new class of through-space charge transfer (TSCT) carbazolylgold(III) C^C^N complexes with unique TADF–TSDP properties by introducing a rigid arylamine on the carbazolyl auxiliary ligand. The highly twisted conformation between the C^C^N and carbazolyl ligands induces strong through-bond ligand-to-ligand charge transfer (TB-LLCT) character in their lowest singlet and triplet excited states, with small singlet–triplet energy gaps for efficient TADF. Moreover, the close spatial proximity between the cyclometalating ligand and the lateral arylamine enables appreciable intramolecular through-space electronic coupling that allows the generation of relatively low-lying triplet through-space ligand-to-ligand charge transfer (³TS-LLCT) excited states. The TADF–TSDP properties are verified by temperature-dependent emission, lifetimes, and ultrafast transient absorption studies. Interestingly, through better alignment with extended planarity and the strengthening of the electron-donating ability of the lateral arylamine, the enhanced through-space electronic coupling can effectively perturb the energies of ³TBCT, ³TSCT, and intraligand (³IL) excited states and thus manipulates the TSDP efficiency. Orange-emitting vacuum-deposited OLEDs made with these gold(III) complexes demonstrate respectable maximum external quantum efficiencies of >10% and long operational half-lifetimes of up to 65,314 h at a luminance of 100 cd m^–2. This work not only demonstrates the realization of interesting TADF–TSDP and TSCT properties in the gold(III) C^C^N cyclometalated system but also enriches the diversity of molecular design for high-performance TSDP and TSCT emitters.