N -Heterocyclic Carbene-Based Tetradentate Platinum(II) Complexes for Deep-Blue Phosphorescent Emitters: Safe Synthesis and Photophysical Study

N-Heterocyclic carbene (NHC)-based tetradentate Pt(II) complexes are promising phosphorescent emitters for full-color displays. However, the conventional synthetic method suffers from high reaction temperatures and low isolated yields and, in particular, poses a risk of explosion. In this work, a safe and practical method is developed using diethylene glycol dimethyl ether (dEGdME) as the solvent at 120 °C, enabling large-scale synthesis of NHC-based Pt(II) complexes with isolated yields of up to 71%. All the developed Pt(II) complexes exhibit deep-blue phosphorescence with full widths at half-maximum (FWHMs) of 20-43 nm and photoluminescence quantum efficiency (PLQY) of up to 85% in dichloromethane at room temperature. This study provides a safe and efficient synthetic method for the large-scale preparation of deep-blue-emitting NHC-based tetradentate Pt(II) complexes, enabling their further application in photophysical property studies.