High‐Energy‐Level TADF Sensitizers Based on Twisted Diphenyltriazine Acceptors for Deep‐Blue Multi‐Resonance OLEDs

Abstract Here, two high‐energy‐level thermally activated delayed fluorescence (TADF) sensitizers (Me‐TRZCz and DMe‐TRZCz) based on twisted diphenyltriazine acceptors for efficient deep‐blue multi‐resonance (MR) organic light‐emitting diodes (OLEDs) are reported. Unlike the analog sensitizer (TRZCz) with planar acceptor, Me‐TRZCz and DMe‐TRZCz, having two steric methyl groups on diphenyltriazine acceptors, exhibit twisted geometry with a distortion angle of ≈30° between peripheral phenyl units and central triazine unit, yielding high S₁/T₁ energies of ≈2.97/2.89 eV that are much higher than those of TRZCz. The increased excited‐state energy level ensures efficient overlap of sensitizer emission with absorption of deep‐blue MR emitter, leading to complete energy transfer from the former to the latter. Consequently, solution‐processed OLEDs employing the sensitizers and a boron, sulfur‐based MR emitter exhibit efficient narrowband deep‐blue electroluminescence with CIE coordinates of (0.13, 0.10), full width at half maximum (FWHM) of 33 nm, and maximum external quantum efficiency of 17.1%, representing state‐of‐the‐art device efficiency for deep‐blue MR OLEDs by solution process.