Facile B–N Covalent Bond Fusion in N , N′ ‐Diaryldihydrophenazines: Achieving Efficient Narrowband Electroluminescence and Controlled Redox Activity

Covalently fusing multiple B–N units into redox‐active polycyclic aromatic hydrocarbons (PAHs) offers a powerful strategy for creating π‐extended systems with novel functionalities, but it remains a formidable challenge. Here, we report a facile, one‐pot, and lithium‐free NH‐directed borylation to construct a series of 5,10‐dihydro‐5,10‐diphenylphenazine (DPPA) derivatives fused by two or four B–N covalent bonds. Such a multiple B–N locking is found not only to enforce molecular rigidity and suppress excited‐state structural relaxation, but also to profoundly modulate the electronic structure and antiaromaticity of the central DPPA core. Interestingly, the resultant quadruply fused system (4BN‐Ph) can function as an unprecedented narrowband orange‐red thermally activated delayed fluorescence (TADF) emitter, enabling efficient electroluminescence with a record‐high external quantum efficiency of 31.2% and a notably small full‐width at half‐maximum of 32 nm at an emissive peak of 595 nm. Also, 4BN‐Ph displays intriguing redox‐controlled properties, since a stepwise oxidation generates near‐infrared‐absorbing open‐shell radical cations and closed‐shell dications. This work establishes a modular route to PAHs incorporating multiple B–N covalent bonds, with exceptional optoelectronic and spintronic properties.