Quenching‐Resistant Efficient OLEDs Based on MR‐TADF Emitters With Donor‐Bridge‐Fluorophore Structure

Abstract The multi‐resonance thermally activated delayed fluorescence (MR‐TADF) emitters hold great promise for organic light‐emitting diodes (OLEDs) due to their narrow‐band emission and high efficiency. However, strong inter‐chromophore interactions in most planar MR‐TADF emitters lead to aggregation at high doping concentrations, resulting in spectral broadening and decreased device efficiency, thereby limiting their practical application. In this work, two MR‐TADF emitters, PPCz‐N‐DtCzB and PPCz‐N‐POAtCzB, are designed and synthesized by incorporating a naphthalene bridge between the MR‐TADF core and peripheral groups. The molecular structure introduces significant steric hindrance, effectively mitigating concentration quenching and spectral broadening. Additionally, PPCz‐N‐DtCzB and PPCz‐N‐POAtCzB exhibit sky blue and pure green emission, peaking at 496 and 515 nm in toluene, respectively. The doped films demonstrate excellent photophysical properties, with photoluminescence quantum yields of 95% and 92%, respectively. At a doping concentration of 5 wt%, the corresponding OLEDs achieve maximum external quantum efficiencies (EQE max ) of 31.5% and 33.1%, respectively. Remarkably, even at a high doping concentration of 30 wt%, they maintain a high EQE max of 30.4% and 27.2%, with minimal variation in their electroluminescence spectra. Furthermore, devices based on PPCz‐N‐POAtCzB exhibit pure green emission across varying doping levels. These results offer valuable insights for the development of concentration‐independent MR‐TADF emitters for high‐performance OLEDs.