Stepwise Molecular Engineering Toward High-Performance Deep-Blue Narrowband OLEDs: Rigidity as the Foundation,...

Developing high-color-purity deep-blue emitters that meet the BT.2020 standard remains a critical challenge in organic light-emitting diodes (OLEDs). Herein, a stepwise molecular engineering strategy for simultaneously accelerating reverse intersystem crossing rate (k_RISC) and narrowing full-width at half maxima (FWHM) is proposed for deep-blue materials. By sequentially enhancing molecular rigidity, strengthening resonant strength, and completing molecular symmetry, a deep-blue emitter (DBNDICz), constructed on modified diboron multiple-resonance scaffold, is developed with peak of 452 nm, ultra-narrow FWHM of 15 nm (0.08 eV) and k_RISC of 3.0 × 10⁵ s^{- 1}. The dominant υ_0-0 transition character of DBNDICz produces a Commission Internationale de I'Éclairage (CIE) coordinates of (0.144, 0.060). Moreover, the expanded conjugated skeleton facilitates horizontal dipole orientation of 93%, leading to a high maximum external quantum efficiency (EQE_max) of 24.2% in bottom-emitting OLEDs. Impressively, top-emitting OLED achieves a record-setting blue index of 514 cd A^{- 1} CIEy^{- 1} with CIE (0.146, 0.036) and EQE_max of 45.2%, establishing a benchmark for state-of-the-art deep-blue devices. Additionally, an operational lifetime (LT₅₀) of 154.2 h is achieved in an anthracene-based host. These results represent one of the best performances reported for deep-blue OLEDs with CIEy≤ 0.06, providing a robust design paradigm for high-performance narrowband deep-blue TADF emitters.