Strategic fluorine atom positioning in carbazolyl oxadiazole derivatives: constructing asymmetric Ir(<scp>iii</scp>) complexes for enhanced electroluminescence performance

Asymmetric coordination Ir(III) complexes hold promise as luminescent materials for organic light-emitting diodes (OLEDs). This study provides an efficient synthetic strategy for the construction of asymmetric complexes through novel carbazolyl oxadiazole-based cyclometalating ligands. This approach circumvents the need for multiple structurally distinct ligands, thereby simplifying the synthetic procedures. Comprehensive characterization of the asymmetric complex (Ir-op-CB) and its symmetric isomers showed that variations in coordination modes had a great impact on their emission properties, enabling a wide range adjustment of luminous colors from green to orange-red. In particular, the complex Ir-op-CB has a high dipole moment and a dominant metal-to-ligand charge transfer nature, resulting in excellent electroluminescence performance. The device incorporating the asymmetric complex Ir-op-CB as the emissive layer achieved a maximum brightness of 11 187 cd m^-2 and a current efficiency of 14.93 cd A^-1. These findings reveal an effective strategy for designing an asymmetric coordination complex to enhance electroluminescence efficiency.