Curved B,N-Doped Nanographene Beyond Narrowband Emission

Intrinsically curved π-frameworks are attractive for emissive materials because their nonplanar geometries can modulate excited-state coupling and create molecular interfaces inaccessible to planar fused systems. Their development, however, is often hindered by enhanced excited-state relaxation and inefficient triplet-exciton utilization. Here, we report a conformationally locked, saddle-shaped pentaboron-embedded B,N-doped nanographene, PB-U. Its rigid skeleton and multiple-resonance electronic structure suppress structural reorganization, while its saddle-shaped framework promotes spin-orbit coupling and facilitates reverse intersystem crossing. As a result, PB-U exhibits green emission in toluene with a full-width at half-maximum of 17 nm, a photoluminescence quantum yield of 98%, and efficient thermally activated delayed fluorescence (TADF) with a reverse intersystem crossing rate of 3.6 × 10⁶ s^-1. The corresponding non-sensitized OLEDs deliver a maximum external quantum efficiency (EQE) of 35.3% with significantly reduced efficiency roll-off, sustaining an EQE of 26.6% even at 10 000 cd m^-2. Beyond efficient narrowband emission, PB-U shows appreciable affinity with C₆₀ through its concave π-surface as demonstrated by their cocrystal structure. These findings identify conformational locking as an effective strategy to exploit both the photophysical and interfacial advantages of curved structure while enabling narrowband, efficient TADF emission.