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

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.