B- and N-embedded color-tunable phosphorescent iridium complexes and B–N Lewis adducts with intriguing structural and optical changes

Abstract

A novel family of B- and N-embedded phosphorescent iridium complexes has been prepared. Single crystal structures indicate that the B-embedded polycyclic unit exhibits better planarity than the N-embedded polycyclic unit, which leads to different π–π-stacking and electrical characteristics. More importantly, by controlling the number of boron or nitrogen atoms embedded, solution-processed OLED devices incorporating these emitters as emitting layers can achieve a phosphorescence color variation from green to deep red (638 nm) and show low-efficiency roll-off and turn-on voltage. In particular, the B-embedded complex Ir-BB shows good color purity with a narrow full width at half maximum (1211 cm⁻¹) and CIE coordinates (0.67, 0.31) in the deep red light region. Notably, B-embedded iridium complexes can also react with two different Lewis bases (pyridine and DMAP) to form intriguing B–N Lewis adducts through different coordination modes. During this process, significantly different structural and optical changes are triggered by the structure and electronic properties of Lewis bases, as confirmed by X-ray crystallographic, ¹H NMR and spectral analysis.