Sterically Regulated Tetradentate Pt(II) Complex for Deep-Blue OLEDs with High Color Purity and Low Efficiency Roll-Off at High Brightness

The realization of deep-blue phosphorescent organic light-emitting diodes (OLEDs) combining high color purity with low efficiency roll-off has proven to be a persistent challenge. Herein, we report a novel tetradentate Pt(II) complex, PtJYCz, based on a synergistic steric engineering strategy. A bulky 3,6-di-tert-butylcarbazole (DTBCz) group was appended to the carbazole moiety to suppress conjugation extension and narrow the emission spectrum, while a 3,3″,5,5',5″-penta-tert-butyl-1,1':3',1″-terphenyl(PTBTP) group was incorporated into the carbene unit to sterically shield the Pt(II) center and suppress intermolecular interactions. As a result, PtJYCz exhibited an ultranarrow deep-blue emission spectrum in solution with a full width at half-maximum (FWHM) of only 15.4 nm and achieved a high photoluminescence quantum yield (ΦPL) of 99% in poly(methyl methacrylate) (PMMA) films. The PtJYCz-based OLED displayed deep-blue electroluminescence peaking at 457 nm with Commission Internationale de l'Éclairage (CIE) coordinates of (0.135, 0.111), delivering a maximum external quantum efficiency (EQE) of 21.7% with suppressed efficiency roll-off, maintaining EQEs of 19.2% and 17.2% at luminance levels of 5000 and 10000 cd/m2, respectively. This work presents a rational molecular design strategy for narrowband deep-blue phosphorescent OLED materials.