Rigidity-Enhanced Narrowband Iridium(III) Complexes with Finely-Optimized Emission Spectra for Efficient Pure-Red Electroluminescence

Attaining phosphorescent materials with narrowband emission is crucial for advancing wide-color-gamut organic light-emitting diode (OLED). Herein, a rigid modification strategy is introduced for iridium(III) complexes to achieve the narrowband red emission with negligible 0-1 peak. By introducing the rigid indolo[3,2,1-jk]carbazole (ICz) into the cyclometalated ligand, Ir(III) complexes, ICziq-Ir and ICzqz-Ir, exhibit pure red phosphorescence with emission peaks at 608 and 613 nm and full widths at half-maximum (FWHMs) of 37 and 38 nm (0.12 and 0.13 eV) in toluene, respectively. Furthermore, the specific site modification of ICzqz-Ir greatly suppresses the high-frequency vibration of the structure, resulting in the narrowband photoluminescent spectrum close to the Gaussian distribution with superior color purity. The OLEDs utilizing ICziq-Ir and ICzqz-Ir demonstrate maximum external quantum efficiencies of 21.4 and 17.8% as well as mild efficiency roll-off. Remarkably, the electroluminescence spectra exhibit similar narrowband red emission with FWHMs of 37 and 43 nm and CIE coordinates of (0.65, 0.35) and (0.66, 0.34), attesting to the excellent color purity of the phosphorescent OLEDs. Through a two-step rigid modification, two narrowband red iridium(III) complexes are prepared with negligible 0-1 peak. The corresponding red phosphorescent organic light-emitting diodes achieved narrow full widths at half-maximum of 37 and 43 nm and external quantum efficiencies of 21.4% and 17.8% with mild efficiency roll-offs. image