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 -conjugated system, this compound has a small Delta E-ST value of 3.6meV and sufficient spin-orbit coupling to exhibit a high-rate constant for reverse intersystem crossing (k(RISC)=1.1 x 10(6)s(-1)). Furthermore, an organic light-emitting diode employing DOB2-DABNA-A as an emitter is fabricated; it exhibits ultrapure deep-blue emission at 452nm with a small full width at half maximum of 24nm, corresponding to Commission Internationale de l'Eclairage (CIE) coordinates of (0.145, 0.049). The high k(RISC) value reduces the efficiency roll-off, resulting in a high external quantum efficiency (EQE) of 21.6% at 1000cdm(-2).