Ultra‐Narrowband Organic Electroluminescence with External Quantum Efficiency of 40% from Indolocarbazole‐Embedded Multiple Resonance Emitters

The demand for ultra‐high‐definition display technology has spurred the prosperity of multiple resonance induced thermally activated delayed fluorescence (MR‐TADF) materials with narrow full‐width at half‐maximum (FWHM) and high efficiency, making them highly promising candidates for high‐color‐purity organic light‐emitting diodes (OLEDs) displays. Indolocarbazole, a highly rigid aza‐polycyclic aromatic hydrocarbon framework, has shown significant potential as a building block for constructing MR‐TADF emitters with ultra‐narrowband emission (< 20 nm). However, it remains a great challenge to construct ultra‐narrowband indolocarbazole‐embedded MR‐TADF emitters with emission maxima less than 500 nm. Here, two MR‐TADF emitters, DBN‐amICz and DBN‐bmICz, are constructed by adopting meta‐N–π–N‐type indolocarbazole as core framework and achieve ultra‐narrowband blue‐green emission in toluene solution with peaks of both 490 nm and FWHMs of 18 and 19 nm, respectively. OLEDs incorporating emitters DBN‐amICz and DBN‐bmICz demonstrate excellent electroluminescence performances, with maximum external quantum efficiencies (EQEs) of 40.1% and 35.5%, and FWHMs of 21 and 24 nm, respectively. This study represents the first report of dual‐boron‐containing MR emitters derived from indolocarbazole with emission below 500 nm, filling a gap in the development of indolocarbazole‐embedded dual‐boron‐containing blue‐green MR‐TADF emitters.