White organic light-emitting diodes (OLEDs) are promising candidates for novel solid-state lighting devices, and high-performance orange light-emitting materials are one of the key factors to realize high-performance complementary color white OLEDs. In this work, we designed a new bipolar cyclometalating ligand by incorporating carbazole moiety with hole-transport ability into 2-phenyl-4-methylquinoline with a large torsion angle. Based on this carbazole-bearing cyclometalating ligand, a pair of orange emissive iridium(III) complexes (Ir1 and Ir2) showing bipolar transport ability are prepared by selecting 2,2,6,6-tetramethylheptane-3,5-dione and picolinic acid as ancillary ligands. Two complexes and the corresponding cyclometalating ligand are well characterized by ¹H and ¹³C nuclear magnetic resonance spectrometry, and mass spectrometry, and the new bipolar cyclometalating ligand and complex Ir1 are also confirmed by X-ray diffraction analysis. The single crystals of Ir1 crystallized in the orthorhombic space group P2₁2₁2₁. Its unit cell parameters are α=β=γ=90°, a=1.271 nm, b=1.522 nm, c=3.161 nm. In O₂-free toluene solution at room temperature, both complexes exhibit intense orange phosphorescence (587 nm for Ir1, 570 nm for Ir2) with high photoluminescent quantum yields of 69% and 74% and with short lifetimes of 1.50 and 1.62 μs. Most importantly, they not only show relatively broad full width at half maximum (FWHM) of 83 nm for Ir1 and 88 nm for Ir2 in their emission spectra but also possess bipolar transport ability, which will be beneficial to realize high-performance electroluminescence. Complex Ir2 is selected as the dopant to fabricate orange OLEDs. The as-prepared OLED realizes a broad orange emission at 569 nm with FWHM of 86 nm, maximum brightness of 4826 cd•m^－2, external quantum efficiency (EQE) of 15%, current efficiency of 35.7 cd•A^－1, and power efficiency of 23.4 lm•W^－1. The results demonstrate that the new bipolar orange emissive iridium(III) complexes designed by incorporating carbazole moiety with hole-transport ability into the cyclometalating ligand with a large torsion angle will be the promising candidates for the future design of high-performance white organic light-emitting diodes.

Key words: iridium(III) complex, carbazole, electroluminescence, phosphorescence, bipolar charge-transport