<i>N</i> ‐heterocyclic carbene‐based tetradentate Pt( <scp>II</scp> ) phosphors for blue organic light‐emitting diodes: Molecular design, photophysics, and device performance

Abstract N ‐heterocyclic carbene (NHC)‐based tetradentate Pt(II) complexes have attracted significant attention as promising phosphorescent dopants for blue organic light‐emitting diodes (OLEDs), because their rigid coordination frameworks enable narrow emission bandwidths and high color purity. However, square‐planar Pt(II) complexes suffer from intrinsic limitations, including limited triplet metal‐to‐ligand charge transfer ( 3 MLCT), long excited‐state lifetimes, and susceptibility to intermolecular interactions in the solid state, which collectively lead to reduced efficiency and operational stability. From a structure‐oriented perspective, this review systematically summarizes recent efforts aimed at overcoming these challenges, focusing on Pt(II) phosphorescent emitters based on the NHC‐phenyl‐O‐carbazole‐pyridine (NHCPhOCzPy) tetradentate ligand framework as a reference scaffold. The photophysical, electrochemical, and thermal properties are compiled together with key OLED device metrics, including emission wavelength, full width at half maximum (FWHM), Commission Internationale de L'Éclairage (CIE) coordinates, external quantum efficiency (EQE), efficiency roll‐off, and operational lifetime. Furthermore, diverse molecular design strategies are discussed, such as suppression of dopant‐dopant and host‐dopant interactions through steric engineering, fused‐ring extension, and enhanced molecular rigidity; modulation of charge injection and emitting dipole orientation by controlling the substituent and electronic‐structure control; and mitigation of intrinsic 3 MLCT limitations through incorporating nitrogen into the NHC framework to shorten decay lifetimes and enhance spin‐orbit coupling. This comprehensive review also critically assesses the trade‐offs among deep‐blue color coordinates, high efficiency, and long device lifetime, and it proposes design guidelines for next‐generation blue Pt(II) phosphorescent dopants.