Topological Structure Optimization of B,N-Doped Nanographenes for Deep-Blue Emitters

B,N-doped nanographenes have been actively studied as blue dopants for OLEDs because of the triplet-exciton harvesting capability and narrowband emission, but their inefficient reverse intersystem crossing (RISC) is a bottleneck for practical applications. The construction of π-extended frameworks is recognized as a general strategy to simultaneously accelerate the RISC process and enhance color purity. However, the influence of topological structure on photophysical properties remains poorly understood. We hereby design three deep-blue, quadruple-borylated nanographenes with isomeric skeletons, and shows a critical dependence of molecular conformation and electronic structure on topology. These compounds, consisting of fused dimers with variable linking sites, range from negatively curved to quasi-planar conformations. Our combined theoretical and experimental analyses indicate that enhanced planarity can facilitate the resonance effect, promote charge transfer delocalization, and increase structural rigidity. Compared to the curved counterparts, the planarized emitter demonstrates multi-dimensional improvement in photophysical properties, achieving an ultranarrow emission spectrum with a full-width at half maximum of 13 nm/0.07 eV and a large RISC rate constant of 2.7×10⁶ s⁻¹. A high external quantum efficiency of 30.4% under a luminance of 1000 cd m^–2 at color coordinates of (0.127, 0.078) is achieved in device without employing additional sensitizer. These findings establish new and unforeseen design guidelines for constructing high-performance narrowband emitters toward ultrahigh-definition displays.