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A new class of thermally activated delayed fluorescence (TADF) tetradentate C ∧ C ∧ N ∧ N ligand-containing gold(III) complexes containing acridinyl moieties has been designed and synthesized. These complexes exhibit orange-red to deep-red emission with photoluminescence quantum yields (PLQYs) of up to 0.76 in solid-state thin films. Short excited-state lifetimes of ≤2.0 μs and large radiative decay rate constants ( k r ) in the order of 10 5 s -1 have also been found in the complexes. High-performance solution-processed and vacuum-deposited organic light-emitting devices (OLEDs) based on these complexes have been fabricated, demonstrating high maximum external quantum efficiencies (EQEs) of 12.2 and 12.7%, respectively, which are among the best values ever reported for red-emitting gold(III)-based OLEDs. In addition, satisfactory operational half-lifetime (LT 50 ) values of up to 34,058 h have been attained in these red-emitting devices. It is found that the operational stability is strongly dependent on the choice of functional groups on the acridinyl moieties, of which the incorporation of -O- and -S- linkers can effectively prolong the LT 50 value by an order of magnitude. The TADF properties of the complexes are substantiated by the hypsochromic shift in emission energies and the remarkable enhancement in the emission intensity upon increasing temperature. The TADF properties have also been supported by temperature-dependent ultrafast transient absorption studies, with the direct observation of reverse intersystem crossing (RISC) and the determination of the activation parameters for the very first time, together with their excited-state dynamics.

A new class of sky-blue-emitting arylgold(iii) complexes containing tridentate bis-cyclometalating ligands derived from 2,6-diphenylpyridine (C^N^C) has been successfully designed and synthesized. By systematically varying the electron-withdrawing groups from cyano, fluoro, and trifluoromethyl to trifluoromethoxy groups on the phenyl ring of the tridentate C^N^C ligands, the emission maxima of these complexes have been significantly blue-shifted from 492 nm to 466 nm in dichloromethane solution. In addition, the higher excited state distortion with respect to the ground state associated with the multiple fluoro substitutions at the tridentate ligand has been successfully reduced by the employment of trifluoromethyl and trifluoromethoxy groups, as revealed by the Huang-Rhys factor. Taking advantage of their high photoluminescence quantum yields of up to 43% in the solid-state MCP thin-films, high performance solution-processable and vacuum-deposited organic light-emitting devices with external quantum efficiencies of up to 5.3% and 11.3%, respectively, have been realized. This work represents the first demonstration of sky-blue-emitting gold(iii) complexes with an x chromaticity coordinate of <0.2.