A Boron, Nitrogen,and Oxygen Doped π-Extended Helical Pure Blue Multiresonant Thermally Activated Delayed Fluorescent Emitter for Organic Light Emitting Diodes That Shows Fast k_RISC Without the Use of Heavy Atoms

Narrowband emissive multiresonant thermally activated delayed fluorescence (MR-TADF) emitters are a promising solution to achieve the current industry targeted color standard, BT.2020, for blue color without using optical filters, aiming for high efficiency organic light-emitting diodes (OLEDs). However, their long triplet lifetimes, largely affected by their slow reverse intersystem crossing rates, adversely affect device stability. In this study, a helical MR-TADF emitter (ƒ-DOABNA) has been designed and synthesized. Because of its π-delocalized structure, ƒ-DOABNA possesses a small singlet-triplet gap, ΔE_ST, and displays simultaneously an exceptionally faster reverse intersystem crossing rate constant, k_RISC, of up to 2 × 10⁶ s⁻¹ and a very high photoluminescence quantum yield, Φ_PL, of over 90% in both solution and doped films. The OLED with ƒ-DOABNA as the emitter achieved a narrow deep-blue emission at 445 nm (full width at half-maximum of 24 nm) associated with CIE coordinates of 0.150, 0.041, and showed a high maximum external quantum efficiency, EQE_max, of ∼20%. © 2024 The Authors. Advanced Materials published by Wiley-VCH GmbH