Modulating the Excited-State Properties of Iridium(III) Complexes for Achieving Narrowband Deep-Red/Near-Infrared Electroluminescence

Developing near-infrared (NIR) iridium(III) complexes with a narrowband emission remains a critical challenge for organic light-emitting diode (OLED) applications. Herein, two structurally simplified complexes, <b>QT-Ir-Me</b> and <b>QT-Ir-tBu</b>, featuring rigid cyclometalated ligands, are successfully developed. Both complexes exhibit deep-red/NIR phosphorescence with emission maxima at 692 nm for <b>QT-Ir-Me</b> and 706 nm for <b>QT-Ir-tBu</b>, with exceptionally narrow full width at half-maximum (FWHM) of 47 nm in a dilute solution. The suppressed spectral broadening can be assigned to dominated triplet ligand-centered charge transition in the excited state and constrained structural distortion, corroborated by minimal root-mean-square deviation of 0.089 and 0.084 for <b>QT-Ir-Me</b> and <b>QT-Ir-tBu</b>, respectively. Moreover, <b>QT-Ir-Me</b> and <b>QT-Ir-tBu</b> exhibit high photoluminescence quantum yields of 53% and 28%, respectively. The doped devices employing <b>QT-Ir-Me</b> and <b>QT-Ir-tBu</b> as emitters exhibit narrowband deep-red/NIR luminescence with FWHMs of 60 and 58 nm, respectively. A <b>QT-Ir-Me</b>-based device demonstrates higher electroluminescence performance with a maximum external quantum efficiency of 6.3%.