含螺环位阻铱(III)配合物的共轭结构调控及其电致发光性能研究

It is an important pathway in the field of phosphorescent organic light-emitting diodes (PhOLED) that endowing iridium (III) emitters with the features of low-cost, decent photoelectric properties, and high doping-concentration application by harmonizing electronic and steric effects of corresponding ligands. Based on our previous research that introducing spiro ligand into Ir^III complexes to protect emitting-center and to suppress concentration quenching, herein, for pushing the emission to orange region, we extend the conjugated structure of spiro[fluorene-9, 9'-xanthene] (SFX) by connected benzo[d]-thiazole-2-yl on the fluorene moiety of SFX via Suzuki-Miyaura coupling, acting as a new spiro ligand. A homoleptic Ir^III complex, fac-Ir(SFXbtz)₃, was synthesized successfully, and the structure and the photophysical and electrochemical properties were studied by nuclear magnetic resonance, single crystal X-ray diffraction, absorption and emission measurements, as well as cyclic voltammetry. The crystallographic data revealed an enlarged Ir…Ir distance and weakly intermolecular π-π interactions between the spiro ligands. The emission spectrum of fac-Ir(SFXbtz)₃ showed a maximum peak at 587 nm and a shoulder peak at 635 nm with a photoluminescence (PL) quantum yield (QY) of 64.7% (relative to tris[2-phenylpyridinato-C², N]iridium(III), PLQY=40%). The highest occupied molecular orbital level was determined to be -5.28 eV according to the onset oxidation potential (0.48 V). In view of the orange light-emitting and the high PLQY of fac-Ir(SFXbtz)₃, the monochromatic and two-element white PhOLED were fabricated to investigate its electroluminescence (EL) performance in high doping concentrations, ω=12% for monochromatic device and ω=15% for two-element white device, respectively. The EL spectrum of the monochromatic PhOLED (device D1) using common 4, 4'-bis(N-carbazolyl)-1, 1'-biphenyl as host exhibits two emission peaks, a maximum emission peak at 581 nm and shoulder emission peak at 631 nm, corresponding to its PL spectrum. The device D1 shows a peak performance of 10.8 cd•A^-1 and 8.4 lm•W^-1, maximum brightness of 7217 cd•m^-2, respectively. The two-element white PhOLED selecting bis[2-(4, 6-difluorophenyl)pyridinato-C², N](picolinato)iridium(III) as complementary blue-light component, possesses a peak performance of 11.6 cd•A^-1 and 8.0 lm•W^-1, maximum brightness of 8763 cd•m^-2, and stabilized CIE 1931 (0.34~0.37, 0.36~0.38) under operated voltages of 3~9 V, respectively. These results indicate that the fac-Ir(SFXbtz)₃ is a potential phosphor for efficient orange PhOLED, possessing the advantages of low-cost, suitable doping in high concentration, and stabilized color coordinates.