Methoxyl modification in furo[3,2-c]pyridine-based iridium complexes towards highly efficient green- and orange-emitting electrophosphorescent devices

Abstract

Two new furo[3,2-c]pyridine-based Ir complexes, namely (4-MeOpfupy)₂Ir(acac) and (3-MeOpfupy)₂Ir(acac), were designed and synthesized by introducing a methoxyl group into the 4- and 3-positions of the phenyl ring on the C^N ligand. It was found that the position of the methoxyl group has an important influence on the electrochemical and photophysical properties, as well as electrophosphorescent device performance. Compared with the reference complex (pfupy)₂Ir(acac) without any methoxyl group (538 nm), (4-MeOpfupy)₂Ir(acac) with a methoxyl group at the 4-position shows a blue-shifted emission peak at 523 nm originating from the methoxyl-induced enhancement of the LUMO level, whereas (3-MeOpfupy)₂Ir(acac) with a methoxyl group at the 3-position shows a red-shifted emission peak at 602 nm originating from the methoxyl-induced enhancement of the HOMO level. The corresponding PhOLEDs based on (4-MeOpfupy)₂Ir(acac) and (3-MeOpfupy)₂Ir(acac) realize highly efficient green and orange electroluminescence with CIE coordinates of (0.37, 0.60) and (0.60, 0.40), revealing a state-of-the-art EQE as high as 29.5% (100.7 cd A⁻¹) and 16.7% (43.9 cd A⁻¹), respectively. These impressive results indicate that methoxyl modification is a valid way to tune the molecular energy levels and emissive color for Ir complexes while not obviously sacrificing the final device performance.