Asymmetric tris-heteroleptic iridium(III) complexes towards blue phosphorescence: Synthesis, photophysics and OLED application.

The development of blue phosphorescent iridium(III) complexes has been a formidable challenge in the field of organic light-emitting diodes (OLEDs). Unlike the conventional blue Ir-complex structure of symmetric tri -/ bis -cyclometalated coordination geometry, we herein report a new configuration of [Ir(C 1 ^N 1)(C 2 ^N 2)(LX)]- tris -heteroleptic Ir(III) complex, where C 1 ^N 1 and C 2 ^N 2 denote two different main ligands, and LX stands for a third ancillary ligand. By the new configuration, two asymmetric blue iridium complexes, namely dfbpy-Ir-dfppy and dfppy-Ir-dfbpy, were designed and synthesized, displaying the highly desirable blue emission peaks at 450 nm and 452 nm, respectively. Based on the two new emitters, the blue OLEDs exhibited good performances with the maximum external quantum efficiency (EQE max) reaching 8.5% and CIE(x, y) coordinates of (0.21, 0.31). This study provides a new strategy for efficient blue iridium complexes through reasonably engineering the asymmetric tris -heteroleptic Ir-complex configuration. [Display omitted] • Two blue isomers possessing the asymmetric tris -heteroleptic [Ir(C 1 ^N 1)(C 2 ^N 2)(LX)]- configuration and their application in OLEDs were rarely reported. • The pure blue emission bands centered around 450 nm, and short lifetimes of 1.67- 3.26 μs. • The blue PHOLED displayed good performances. [ABSTRACT FROM AUTHOR]