Precise Multi‐Site Borylation Engineering of Indolo[2,3‐c]Carbazole‐Bridged Narrowband MR‐TADF Emitters

ABSTRACT Indolocarbazole‐bridged double‐boron multi‐resonance thermally activated delayed fluorescence (MR‐TADF) materials enable precise modulation of emission colors while retaining ultra‐narrowband characteristics in organic light‐emitting diodes (OLEDs). Herein, we first introduce indolo[2,3‐c]carbazole (23cIC) into the design of MR‐TADF emitters and develop an electronically and sterically controlled multi‐site borylation strategy. This strategy affords the electronically favored exo‐configuration for Tbu‐exo, which exhibits narrowband green emission at 524 nm with a full‐width at half‐maximum (FWHM) of 20 nm, while yielding the steric hindrance‐guided endo‐configuration for Ad‐tph‐endo exhibiting by yellow emission at 566 nm with a FWHM of 25 nm. Notably, the endo‐configuration gives rise to ( P / M )‐Ad‐tph‐endo, which exhibits significant chiral luminescence properties. Vacuum‐deposited OLEDs based on Tbu‐exo and Ad‐tph‐endo exhibit emission peaks at 530 nm (FWHM = 27 nm) and 568 nm (FWHM = 33 nm), respectively, both achieving external quantum efficiencies (EQE) exceeding 30%. Furthermore, we fabricated solution‐processed top‐emitting OLEDs based on Tbu‐exo for the first time, which realize ultra‐narrow pure‐green emission with CIE coordinates of (0.21, 0.75)—closely approaching the BT.2020 green standard—and a record‐high current efficiency of 200.9 cd A −1 .