The ultra-high definition (UHD) displays in the market require organic light-emitting diodes (OLEDs) to meet the Rec.2020 color gamut standard, while it is still challenging to exploit ultra-deep-blue emitters that satisfy such blue standard. Herein, by substituting tCz (3,6-di(tert-butyl)carbazole) donor unit on the robust BOC (8,8,12,12tetramethyl-8,12-dihydro-4-oxa-3a2-boradibenzo[cd,mn]pyrene) acceptor unit with high structural rigidity and appropriate energy levels, a novel boron-based D-A type thermally activated delayed fluorescence (TADF) ultradeep-blue emitter, namely, tCz-BOC, was readily designed and synthesized. Inheriting from its rigid organoboron core, the emitter presents ultra-deep-blue emission with narrow spectral full width at half maximum (FWHM) of 54 nm and high photoluminescence quantum yield up to 73.7%. Additionally, tCz-BOC can effectively harvest T1 excitons through high-lying T2 mediated reverse intersystem crossing process. As a consequence, the fabricated OLED based on tCz-BOC exhibits a satisfactory ultra-deep-blue emission with lambda EL of 424 nm, narrow emission bandwidth with FWHM of 47 nm, excellent maximum external quantum efficiency (EQEmax) of 13.9%, as well as the CIEy coordinate of 0.047, which is fairly close to the Rec.2020 blue color gamut.
