Carbazole‐based DABNA analogues (CzDABNAs) were synthesized from triarylamine by regioselective one‐shot single and double borylation. The reaction proceeded selectively at the ortho position of the carbazolyl group, where the highest occupied molecular orbital is mainly localized owing to the difference in the electron‐donating abilities of the diarylamino and carbazolyl groups. The facile and scalable method enabled synthesis of CzDABNAs, exhibiting narrowband thermally activated delayed fluorescence with emission spectra ranging from deep blue to green. The organic light‐emitting diode devices employing these products as emitters exhibited deep‐blue, sky‐blue, and green emission with high external quantum efficiencies of 19.5, 21.8, and 26.7 %, respectively.

Efficient thermally activated delayed fluorescence materials based on the multiple resonance effect were synthesized by nucleophilic substitution and electrophilic C–H borylation, featuring a small energy gap between the singlet and triplet state, high photoluminescence quantum yield, and narrow emission band. Organic light-emitting diodes employing these materials as emitters exhibited sky-blue emission with a high external quantum efficiency of 21.4% and a narrow full width at half-maximum of 33 nm.

Herein, we reported an ultrapure blue multipleresonance-induced thermally activated delayed fluorescence (MR-TADF) material (n-DABNA-O-Me) with a high photoluminescence quantum yield and a large rate constant for reverse intersystem crossing. Because of restricted p-conjugation of the HOMO rather than the LUMO induced by oxygen atom incorporation, n-DABNA-O-Me shows a hypsochromic shift compared to the parent MR-TADF material (n-DABNA). An organic light-emitting diode based on this material exhibits an emission at 465 nm, with a small full-width at halfmaximum of 23 nm and Commission Internationale de lEclairage coordinates of (0.13, 0.10), and a high maximum external quantum efficiency of 29.5 %. Moreover, n-DABNA-O-Me facilitates a drastically improved efficiency roll-off and a device lifetime compared to n-DABNA, which demonstrates significant potential of the oxygen atom incorporation strategy.

Research data are not shared.

Multiple-resonance thermally activated delayed fluorescence (MR-TADF) emitters have emerged as an important component of organic light-emitting diodes (OLEDs) because of their narrowband emission and high exciton utilization efficiency. However, the chemical space of MR-TADF emitters remains mostly unexplored because of the lack of suitable synthetic protocols. Herein, we demonstrate a sequential multiple borylation reaction that provides new synthetically accessible chemical space. ω-DABNA, the proof-of-concept material, exhibited narrowband green TADF with a full width at half-maximum of 22 nm and a small singlet−triplet energy gap of 13 meV. The OLED employing it as an emitter exhibited electroluminescence at 512 nm, with Commission International de l'E ́clairage coordinates of (0.13, 0.73) and a high external quantum efficiency (EQE) of 31.1%. Moreover, the device showed minimum efficiency roll-off, with an EQE of 29.4% at 1000 cd m −2 .