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

Abstract

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(C1^N1)(C2^N2)(LX)]-tris-heteroleptic Ir(III) complex, where C1^N1 and C2^N2 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 (EQEmax) 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.