Narrowband blue emitter based on fused nitrogen/carbonyl combination with external quantum efficiency approaching 30%

Multi-resonance thermally activated delayed fluorescence (MR-TADF) emitters can enable narrowband emission with high color purity and electroluminescence efficiency. Nitrogen/carbonyl (N/C=O) system is receiving increasing attention while the nitrogen/boron (N/B) system has been widely studied. Donor decoration is an effective approach for N/B type MR-TADF system but always leads to broadening and red-shifting of the emission band in N/C=O MR-TADF system. We attribute these unfavorable phenomena to the formation of intramolecular charge transfer between the MR-core and peripheral donors. To address this issue, we have developed a new strategy by decorating DMQAO (a fused N/C=O MR-core) with a triazine acceptor and a neutral terphenyl group to construct MTDMQAO and MBDMQAO, respectively. The introduction of the triazine acceptor not only realizes efficient narrowband emission in MTDMQAO, but also accelerates the reverse intersystem crossing process through enhanced spin-orbital coupling. As a result, MTDMQAO exhibits a significantly higher external quantum efficiency of 29.4% compared to the referent emitters, validating the rationality of our derivation strategy. This study highlights the potential of the N/C=O system for MR-TADF emitters and provides important insights for understanding the difference between N/B and N/C=O systems.