Enhanced deep red to near-infrared (DR-NIR) phosphorescence in cyclometalated iridium(iii) complexes

Abstract

The design of deep-red to near-infrared (DR-NIR) phosphorescent compounds with high photoluminescence quantum yields (Φ_PL) is a significant fundamental challenge that impacts applications including optoelectronic devices, imaging, and sensing. Here we show that bis-cyclometalated iridium complexes with electron-rich ancillary ligands can have exceptional quantum yields for DR-NIR phosphorescence (peak λ > 700 nm). Six bis-cyclometalated iridium(III) complexes with DR-NIR phosphorescence are described in this work, pairing highly conjugated cyclometalating ligands with electron-rich and sterically encumbered β-ketoiminate (acNac), β-diketiminate (NacNac), and N,N′-diisopropylbenzamidinate (dipba) ancillary ligands. The photoluminescence spectra and quantum yields are solvent-dependent, consistent with significant charge-transfer character in the emissive excited state. The ancillary ligands perturb the excited-state kinetics relative to closely related compounds, which can lead to enhanced Φ_PL values in the DR-NIR region, particularly in toluene solution and in doped polymer films.