Cyano‐Substituted Platinum(II) Complexes for Highly Efficient Deep‐Blue Phosphor‐Sensitized Fluorescent OLEDs

ABSTRACT Tetradentate Pt(II) complexes are promising phosphorescent materials for achieving high‐performance deep‐blue organic light‐emitting diodes (OLEDs). However, their molecular designs have traditionally relied on incorporating complex, bulky substituents to prevent stacking‐induced photophysical anomalies arising from their inherently planar structures. Here, we present a simple yet highly effective alternative: introducing a non‐bulky cyano (CN) group at the para‐position of the Pt‐phenyl bond. This subtle modification not only suppresses exciplex emission but also enhances the photoluminescence quantum yield by mitigating both temperature‐dependent and temperature‐independent nonradiative decay processes. Utilizing the CN‐substituted Pt complex as a phosphorescent sensitizer, paired with a multi‐resonance thermally activated delayed fluorescent emitter, we demonstrate a deep‐blue phosphor‐sensitized fluorescent (PSF) OLED achieving a maximum external quantum efficiency (EQE) of 31.7% ± 0.9% and a Commission Internationale de l’Éclairage y ‐coordinate below 0.1. Notably, the PSF OLED sustains a high EQE of 25.4% ± 0.8% even at the practical luminance of 1000 cd/m 2 . This simultaneous achievement—remarkable given the persistent trade‐off between efficiency and spectral purity in the deep‐blue regime – establishes a simple yet powerful strategy for advancing efficient deep‐blue OLEDs based on Pt(II) complexes.