Steric Hindrance and Extended Conjugation in Pt-Based Phosphors Using a Rigid Four-Coordinate Organoboron Skeleton...

Excimer-based single-dopant white organic light-emitting diodes (WOLEDs) are promising for lighting applications. However, achieving high efficiencies and high color rendering index (CRI) values simultaneously remains challenging. To address this issue, herein, we successfully used a rigid four-coordinate organoboron skeleton to develop highly emissive bluish-green Pt(II) complex phosphors Pt0F and Pt1F featuring red excimer emission. Steric hindrance from the two branched ancillary phenyl rings of the four-coordinate organoboron skeleton helps suppress aggression quenching. The coplanar 2-phenylpyridine (ppy) moiety of the four-coordinate organoboron skeleton extends the π-conjugation length of the bipyridine-based Pt(II) complexes, resulting in more red-shifted excimer emission. Interestingly, Pt0F and Pt1F present a monomer emission with two comparable sky-blue and green emission bands and a red excimer emission in highly doped PMMA films, which would facilitate high CRI values for WOLEDs. Excitedly, both Pt0F and Pt1F can exhibit high photoluminescence quantum yields (PLQYs) over 0.80 in all tested doped PMMA films, indicating high PLQYs of monomer and excimer emission. More importantly, most of the excimer-based single-dopant yellowish WOLEDs based on Pt0F and Pt1F can give high external quantum efficiencies over 21.2% and maximum up to 23.8% with high CRI values over 81 and maximum up to 89, representing an important advance in Pt(II) complex-type excimer-based single-dopant WOLEDs.