Managing Intersegmental Charge-Transfer and Multiple Resonance Alignments of D₃-A Typed TADF Emitters for Red OLEDs with Improved Efficiency and Color Purity

Thermally activated delayed fluorescence (TADF) emitters induced by the multiple resonance (MR) effect have garnered considerable attention. However, it is difficult to develop MR-TADF emitters that maintain high color purities in the red region. In this work, the importance of excited state alignments of MR-based donor-acceptor (D-A) molecules in determining their preferring characteristics is clarified. By using the newly designed molecule mBDPA-TOAT whose apparent excited states show hybridization of MR and intersegmental charge-transfer features as an emitter in an organic light-emitting diode (OLED), a high external quantum efficiency of 17.3% is achieved with a full width at half-maximum of 45 nm (154 meV) and Commission Internationale de L'Éclairage coordinate of (0.61, 0.39). This work demonstrates when introducing D-A typed structures, features, and alignments of molecular excited states determine ultimate material properties. This could help to develop high efficiency and high color purity TADF emitters toward long wavelength range.