A facile color-tuning strategy for constructing a library of Ir(iii) complexes with fine-tuned phosphorescence from bluish green to red using a synergetic substituent effect of –OCH3 and –CN at only the C-ring of C^N ligand

Abstract

By simply grafting a –CN group and/or a –OCH₃ group onto the meta- and/or para-site of the C-ring, a series of Ir(III) complexes bearing a similar molecular platform of bis(1,2-diphenyl-1H-benzimidazolato-N,C^2′)iridium(III)(acetylacetonate), but showing fine-tuned phosphorescence covering nearly the whole window of the visible spectrum with a wide color-tuning range of 109 nm was acquired. With the help of DFT calculations, it was revealed that if the C-related arene moiety of the C^N ligand (C-ring) contributes substantially to both the HOMO and LUMO of an Ir(III) complex, the concurrent introduction of an electron-donating –OCH₃ and an electron-withdrawing –CN groups on the C-ring at the meta- and para-sites relative to the Ir atom may lead to a favorable synergetic substituent effect on the color-tuning direction. This may represent a facile yet effective molecular design strategy for Ir(III) complexes with a desirous emission color. A bluish green organic light-emitting diode (OLED) based on one of the objective complexes displayed a maximum current efficiency of 62.1 cd A⁻¹, an external quantum efficiency of 19.8%, and a brightness of 48 040 cd m⁻², implying that high-performance red and blue OLED phosphors as well as libraries of Ir(III) complexes bearing similar molecular platforms may be developed through this –OCH₃ and –CN synergetic substitution strategy.