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.