Highly efficient multi-resonance thermally activated delayed fluorescence material toward a BT.2020 deep-blue emitter

An ultrapure deep-blue multi-resonance-induced thermally activated delayed fluorescence material (DOB2-DABNA-A) is designed and synthesized. Benefiting from a fully resonating extended helical π-conjugated system, this compound has a small ΔEST value of 3.6 meV and sufficient spin–orbit coupling to exhibit a high-rate constant for reverse intersystem crossing (kRISC = 1.1 × 106 s–1). Furthermore, an organic light-emitting diode employing DOB2-DABNA-A as an emitter is fabricated; it exhibits ultrapure deep-blue emission at 452 nm with a small full width at half maximum of 24 nm, corresponding to Commission Internationale de l’Éclairage (CIE) coordinates of (0.145, 0.049). The high kRISC value reduces the efficiency roll-off, resulting in a high external quantum efficiency (EQE) of 21.6% at 1000 cd m–2. The realization of a BT.2020 blue emitter is challenging due to the spectral redshift associated with π-extension. Here, the authors report a multi-resonance thermally activated delayed fluorescence emitter, exhibiting ultrapure deep-blue narrow emission and CIEy ≤ 0.05 exceeding 20% efficiency.