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

AbstractNarrowband 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 (f‐DOABNA) has been designed and synthesized. Because of its π‐delocalized structure, f‐DOABNA possesses a small singlet‐triplet gap, ΔEST, and displays simultaneously an exceptionally faster reverse intersystem crossing rate constant, kRISC, of up to 2 × 106 s−1 and a very high photoluminescence quantum yield, ΦPL, of over 90% in both solution and doped films. The OLED with f‐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, EQEmax, of ∼20%.This article is protected by copyright. All rights reserved