Boosting the efficiency of deep-red Ir(iii) complexes by modulating nitrogen atoms for high-performance OLEDs

Abstract

Constructing deep-red Ir(III) phosphors featuring sufficient luminous efficiency is highly desirable but remains challenging owing to their severe nonradiative decay. Herein, two structurally simple Ir(III) complexes, namely Ir(iqbt)₂IPO and Ir(qabt)₂IPO, with cyclometalated ligands modulated by nitrogen atoms were developed. Both complexes showed efficient deep-red phosphorescence with the desired emission peaked at approximately 680 nm and shoulder peaks at 735 nm. Complex Ir(qabt)₂IPO with a high nitrogen atom doping ratio exhibited a much higher emission intensity accompanied by a better PLQY of 21.4% relative to that of Ir(iqbt)₂IPO (16.3%). Analysis of the excited electronic structures of both complexes indicated that such high emission efficiency could stem from the augmentation of the MLCT character. Consequently, Ir(qabt)₂IPO based OLED displayed more than twofold improvement in the maximum external quantum efficiency, exceeding that of Ir(iqbt)₂IPO and affording the deep-red electroluminescence with CIE coordinates at (0.72, 0.27). Therefore, designing cyclometalated ligands by introducing extra nitrogen atoms provides an effective strategy for exploring deep-red Ir(III) complexes and OLEDs.