High-Color-Purity Blue OLEDs with a Small Efficiency Roll-Off Enabled by a Cyanoregulated Tetradentate Platinum(II) Complex

Organic light-emitting diodes (OLEDs) have emerged as a pivotal technology for full-color displays, and emitters are critical to their device performances. This work developed a new tetradentate Pt(II) emitter, PtON-CN, through a cyano (CN) group functionalization at the phenyl moiety. The CN group could modulate its frontier molecular orbital energy levels, especially deepen its lowest unoccupied molecular orbital (LUMO) level, and improve the electron injection ability from the hole-blocking layer to the emissive layer in the device setting. The CN group also reduced the excited-state deformation and resulted in an improved color purity. In dichloromethane solution, PtON-CN exhibited narrow emission with a small full width at half-maximum (FWHM) of 21 nm and a small Huang-Rhys factor (<i>S</i>_M) of 0.386. The PtON-CN-doped poly(methyl methacrylate) (PMMA) film demonstrated a short excited-state lifetime of 2.7 μs and a high quantum efficiency of 95%. The PtON-CN device exhibited a narrow emission spectrum peaking at 466 nm with a small FWHM value of 20 nm, resulting in a Commission International de I'Eclairage <i>y</i>-coordinate (CIE_<i>y</i>) of 0.145. The PtON-CN device also showed a maximum external quantum efficiency (EQE_max) of 20.6% and maintained an EQE of 19.9% at 1000 cd/m², suggesting a small efficiency roll-off of only 3.4%.