Carbonyl Fused Organoboron Polycyclic Aromatic Hydrocarbon for Bathochromic‐Shifted Narrowband OLED

Abstract Polycyclic aromatic hydrocarbon (PAH) compounds are prospective materials for highly efficient narrowband organic light‐emitting diodes. Specifically, boron‐nitrogen doped PAHs exhibit multiple resonance (MR) effect toward thermally activated delayed fluorescence (TADF) and narrow full width at half‐maximum (FWHM). Currently, the molecular design strategy for bathochromic‐shifted narrowband MR‐TADF emitters is a hotspot and challenging puzzle. Herein, a carbonyl is fused in the boron‐nitrogen doped PAH for constructing a boron/nitrogen/carbonyl MR‐TADF emitter. Benefiting from the carbonyl, the developed emitter exhibits enhanced intramolecular charge transfer and decreased reorganization energy, which displays bathochromic‐shifted narrowband emission pertinently. As a consequence, the proof‐of‐concept compound TCZBAO achieves an emission peak at 522 nm and narrow FWHM of 39 nm, while the carbonyl‐free TCZBAC exhibits an emission peak at 502 nm and FWHM of 46 nm. Maximum external quantum efficiencies of 36.1 % and 32.4 % are realized for the devices based on TCZBAO and TCZBAC, respectively, indicating the guiding significance of the proposed design strategy for developing bathochromic‐shifted narrowband MR‐TADF emitters.