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-pi-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 (EL) 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.