Blue multiple resonance emitters exhibiting fast spin flip

The ongoing pursuit of developing high-performance narrowband blue multiple resonance (MR) emitters that feature a fast reverse intersystem crossing (RISC) rate (k_RISC) presents a significant challenge. To address this, we introduce an efficient approach: The “space-confined acceptor-donor-acceptor (SCADA)” strategy, aiming at accelerating the RISC process in the development of blue MR emitters. By integrating two cyanobenzene acceptors and one carbazole donor onto the MR skeleton results, we achieve a blue-shifted emission with a reduced full width at half maximum (FWHM). This structural arrangement encourages the donor and acceptor units to align face-to-face at close proximity, which leads to intramolecular noncovalent interactions and enhances spin-orbit coupling. Consequently, the “SCA-DA” strategy gives rise to a superior blue MR emitter characterized by a small FWHM of 19 nm, a fast k_RISC of 1.8 × 10⁶ s⁻¹, as well as a fast radiative decay rate (k_R) of 2.0 × 10⁸ s⁻¹. These attributes facilitate the assembly of high-performance narrowband blue organic light-emitting diodes with a high maximum external quantum efficiency of 30.2% and low efficiency roll-off.