o‐ Carborane‐based multi‐resonance thermally activated delayed fluorescence emitter exhibits highly efficient and multifunctional electroluminescence

Abstract o ‐Carborane is widely used in designing multifunctional organic luminescent emitters. However, these derivatives often suffer from inefficient exciton utilization and competing energy pathways, leading to poor electroluminescent performance. In this study, two multifunctional materials, DBN‐ o Cb and DBN‐ o Cb‐2, were synthesized by embedding blue‐ and green‐emitting boron/nitrogen multiple resonance (B/N‐MR) units into ortho ‐carborane scaffolds. Exciton dynamics analysis showed that the localized excitation energy of DBN‐ o Cb could be effectively transferred via the Förster resonance energy transfer process, avoiding competition with photoinduced electron transfer. The rigid structures, formed by B/N‐MR fragments and o ‐carborane units, help reduce non‐radiative decay. Further investigation of exciton dynamics through femtosecond transient absorption studies indicates the presence of multiple distinct energy transfer pathways for DBN‐ o Cb. The corresponding organic light‐emitting diode based on DBN‐ o Cb achieved a record external quantum efficiency of 22.3%, the highest reported for red‐organic light‐emitting diodes with o ‐carborane‐based emitters.