Achieving narrowband deep-blue electroluminescence (CIEy = 0.04) via a fluorinated and sterically modulated MR-TADF emitter

Abstract

Moving toward next-generation ultrahigh-definition displays, achieving narrowband deep-blue organic light-emitting diodes (OLEDs) that satisfy the stringent Recommendation ITU-R BT.2020 (Rec.2020) color target remains challenging. Here we report 4FBN-Me, a fluorinated and sterically modulated multi-resonance thermally activated delayed fluorescence (MR-TADF) emitter based on a boron–nitrogen framework. 4FBN-Me can be synthesized via a lithium-free, high-yield borylation reaction. Photophysical investigations reveal narrowband blue emission with a full width at half maximum (FWHM) of 24 nm in solution, a high photoluminescence quantum yield (PLQY) of 75.8%, and delayed fluorescence with a reverse intersystem crossing rate (k_RISC) of 2.32 × 10⁵ s⁻¹. The corresponding vacuum-deposited OLEDs deliver deep-blue electroluminescence peaking at 440 nm with a FWHM of 27 nm, Commission Internationale de l’Éclairage (CIE) coordinates of (0.154, 0.040), and a maximum external quantum efficiency (EQE_max) of 12.71%. These results demonstrate that fluorination combined with minimal steric modulation is an effective molecular design strategy for achieving narrowband deep-blue MR-TADF emitters with promising electroluminescence performance.