Regioselective Acylation for the Versatile Synthesis of Carbonyl‑Functionalized Boron-Based Multiple Resonance Emitters.

Multiple resonance (MR) emitters have attracted considerable attention owing to their narrowband emission and high efficiency in organic light-emitting diodes (OLEDs). Although carbonyl incorporation into MR frameworks is an effective strategy for enhancing spin-related excited-state processes, synthetic approaches for introducing carbonyl groups into MR skeletons remain highly limited. Herein, we report a regioselective late-stage acylation strategy for boron-based MR emitters using readily accessible acid chlorides. The reaction proceeds without Lewis acid catalysts and exhibits broad substrate scope with excellent regioselectivity. Comparative experiments together with DFT calculations revealed that the unique MR-type electronic structure of the DABNA framework promotes unusual regioselective C─C bond formation over conventional N-acylation pathways. The resulting acylated intermediates were further transformed into fused-ring carbonyl-functionalized MR emitters through intramolecular cross-coupling reactions. Furthermore, the resulting acylated intermediates serve as versatile synthetic platforms for the development of advanced MR emitters. Photophysical and theoretical analyses demonstrated that carbonyl incorporation enhances spin-orbit coupling (SOC) and activates ISC/RISC processes, leading to distinct thermally activated delayed fluorescence behavior. This strategy substantially expands the accessible chemical space of MR emitters and provides a versatile platform for developing advanced MR-TADF materials.