In this study, a tetradentate Pt(II) complex designed to have N-heterocyclic carbene ligands modified with an anchor-shaped 2,6-diisopropylphenyl (dip) group is described to enhance molecular rigidity for narrow emission and high efficiency. The tetradentate ligand with the dip group significantly hinders steric interactions and restricts π-conjugation from benzocarbene, leading to shallow lowest unoccupied molecular orbital levels and a consequent reduction in the triplet metal-to-ligand charge transfer character. These structural modifications result in narrow emission spectra and enhanced efficiency for blue organic light-emitting diodes (OLEDs) over wide doping concentration ranges. These blue OLEDs exhibit deep-blue emissions at 455 nm with color coordinates of (0.139, 0.090), a full width at half-maximum of 17 nm, and a high maximum external quantum efficiency of 24.1% at a doping concentration of 10 wt %. In addition, the OLED performance was stably maintained at a doping concentration of 20 wt %. Overall, the anchor-shaped dip group significantly enhances the rigidity of the ligand in the tetradentate Pt(II) complex, effectively reducing intermolecular interactions and allowing the complex to function as a highly efficient and pure deep-blue emitter.
Keywords: N-heterocyclic carbene; deep-blue emitter; high efficiency; narrowband emission; organic light-emitting diodes; phosphorescence; tetradentate Pt(II) complex.