Design and Characterization of a New Phenoxypyridine–Bipyridine-Based Tetradentate Pt(II) Complex Toward Stable Blue Phosphorescent Emitters

Although various phosphorescent organic light-emitting diodes (PhOLEDs) have been developed, their lifetimes remain shorter than those of fluorescent OLEDs. In this study, a novel Pt(II) complex featuring a tetradentate ligand composed of bipyridine and phenoxypyridine, referred to as <b>LL-O</b>, was synthesized and fully characterized to evaluate its potential as a dopant for PhOLEDs. Geometry-optimized calculations indicate that <b>LL-O</b> adopts a distorted square-planar structure around the Pt(II) center. The complex displays bluish-green emission with maxima at 490 and 518 nm. However, it exhibits a low photoluminescence quantum yield (4%), primarily due to a dominant non-radiative decay rate that surpasses the radiative decay rate. Natural transition orbital analysis reveals that the emission of <b>LL-O</b> originates from a combination of triplet ligand-centered (³LC), triplet ligand-to-ligand charge-transfer (³LL'CT), and triplet metal-to-ligand charge-transfer (³MLCT) transitions. This compound also demonstrates high thermal stability (decomposition temperature > 340 °C) and an appropriate HOMO energy level (-5.58 eV), making it suitable for use as a dopant in versatile PhOLEDs.