Synthesis and Characterization of New Solution-Processable Red Iridium (III) Complexes Based on a Phenylation Strategy

Abstract

The exploitation of high-performance solution-processable phosphorescence organic light-emitting diode (PhOLED) materials is of great significance for the realization of large-area, low-cost and flexible display. On the basis of our previous findings that the para-phenylation (phenyl or 4-methoxyphenyl, with respect to the C-Ir bond) on the cyclometalated ligand (C^N ligand) of bis[2-phenylbenzothiazolato-N,C2']iridium(III)(acetylacetonate) can result in compounds with drastically enhanced film amorphism hence much improved electroluminescence (EL) performance, herein, this para-phenylation strategy was applied to Ir(III) complexes bearing a molecular platform of orange-emissive bis[2-(6-diphenylamino)phenylbenzothiazolato-N,C2']iridium(III)(acetylacetonate)[(Nbt)2Ir(acac)] to afford two new Ir(III) complexes, namely (3PhNbt)2Ir(acac) and (3OMePhNbt)2Ir(acac). X-ray diffraction (XRD) characterization results revealed that both the two objective compounds possess much enhanced film amorphism than their parent compound (Nbt)2Ir(acac), validating the efficacy of this para-phenylation strategy in achieving Ir(III) complexes with enhanced film amorphism. Addi-tionally, in comparison with (Nbt)2Ir(acac), both (3PhNbt)2Ir(acac) and (3OMePhNbt)2Ir(acac) show much enhanced solubility in common organic solvents, together with 5~10 nm bathochromic-shifted phosphorescence band to red region. As a consequence, (3PhNbt)2Ir(acac) and (3OMePhNbt)2Ir(acac) were expected to be promising guest materials for the fabrication of high-performance solution-processed red PhOLEDs. EL characterization results indicated that for single-layer red solu-tion-processed PhOLEDs using (3PhNbt)2Ir(acac) and (3OMePhNbt)2Ir(acac) as the guest dopant, they show peak current efficiency of 2.4 cd·A-1 and 8.7 cd·A-1, maximum brightness of 1830 cd·m-2 and 6630 cd·m-2, and CIE coordinates of (0.61, 0.39) and (0.62, 0.38), respectively. In contrast, the contral device based on the orange-emissive (Nbt)2Ir(acac) only shows a peak current efficiency of 1.5 cd·A-1, maximum brightness of 1620 cd·m-2, and CIE coordinates of (0.59, 0.41). These results confirmed that para-phenyl modification on the C^N ligand (with respect to the C-Ir bond) is indeed an effective approach to acquiring high-performance solution-processable PhOLED Ir(III) complexes with simultaneously red-shifted emission band.