An ultrapure deep-blue multi-resonance-induced thermally activated delayed fluorescence (TADF) material, DOB2-DABNA-A, has been designed and synthesized. This material exhibits a small ΔE_ST value of 3.6 meV and high reverse intersystem crossing (k_RISC) of 1.1 × 10⁵ s⁻¹. An organic light-emitting diode (OLED) using DOB2-DABNA-A as an emitter shows ultrapure deep-blue emission at 452 nm with a full width at half maximum of 24 nm, corresponding to Commission Internationale de l’Eclairage (CIE) coordinates of (0.145, 0.049). The high k_RISC value reduces efficiency roll-off, achieving a maximum external quantum efficiency (EQE) of 21.6% at 1000 cd m⁻². This material meets the BT.2020 standard requirements for UHD displays, making it a promising candidate for OLED devices.An ultrapure deep-blue multi-resonance-induced thermally activated delayed fluorescence (TADF) material, DOB2-DABNA-A, has been designed and synthesized. This material exhibits a small ΔE_ST value of 3.6 meV and high reverse intersystem crossing (k_RISC) of 1.1 × 10⁵ s⁻¹. An organic light-emitting diode (OLED) using DOB2-DABNA-A as an emitter shows ultrapure deep-blue emission at 452 nm with a full width at half maximum of 24 nm, corresponding to Commission Internationale de l’Eclairage (CIE) coordinates of (0.145, 0.049). The high k_RISC value reduces efficiency roll-off, achieving a maximum external quantum efficiency (EQE) of 21.6% at 1000 cd m⁻². This material meets the BT.2020 standard requirements for UHD displays, making it a promising candidate for OLED devices.