Design and Synthesis of Asymmetric Au(III) Complexes Exhibiting Bright Anisotropic Emission for High-Performance Organic Light-Emitting Diodes

Organic light-emitting diodes (OLEDs) are emerging as one of the most promising candidates for next-generation optoelectronics. However, most commercial OLEDs are based on rare-metal organometallic emitters, which bring challenges towards sustainable technology. Recent development of earth-abundant gold complexes has drawn a lot of attention, whereas the device efficiencies remain lower than the rare-metal counterparts. Here, we present rational molecular design of a series of Au(III) organometallic complexes consisting of asymmetric C^C^N ligands and carbazole moieties functionalized by phenyl or mesityl groups. The synthesized complexes exhibit shortened radiative lifetimes, and reach improved photoluminescence quantum yield, <i>η</i>_PL, of greater than 93% in thin films. Moreover, the asymmetric molecular design induces anisotropic emission with a high ratio of horizontally oriented transition dipole moment of up to 82% in host-guest films. Our computational results corrborated our experiemtnal data. It suggested that the asymmetric motifs of emitters give rise to pertubation in eletrostatic potential distribution. As a result, our chemically asymmetrical Au(III) complexes orient horizontally in bipolar host, 26DCzPPy, enchancing light out-coupling efficiency. Accordingly, we demonstrate high-performance OLED devices with record-high external quantum efficiencies, <i>η</i>_ext, and current efficiencies, <i>η</i>_CE, of up to 27% and 89 cd A^-1, respectively. We believe that the molecular design of anisotropic Au(III) emitters will be greatly facilitated by the fundamental principles and theoretical analysis presented here.