1,4-Oxaborine fusion as an atom-precise strategy for efficient narrowband polycyclic aromatic hydrocarbon emitters and hybridized local and charge-transfer sensitizers.

Polycyclic aromatic hydrocarbons (PAHs) possess rigid π-conjugated frameworks and intrinsically narrow emission profiles; however, their practical application as emitters is often limited by low photoluminescence quantum yields (PLQYs) arising from symmetry-restricted transitions. We present a general, atom-precise design strategy that overcomes this limitation via 1,4-oxaborine fusion. By annulating a boron/oxygen-containing unit onto representative PAH cores, this approach simultaneously introduces moderate charge-transfer character and preserves substantial locally excited character within a rigid framework. The resulting 1,4-oxaborine-fused PAHs exhibited markedly enhanced PLQYs exceeding 60% and radiative decay rates approaching 108 s-1 while maintaining relatively narrow emission bandwidths. This molecular design enables the realization of high emission efficiency and color purity, overcoming a long-standing limitation of PAH-based emitters. Furthermore, the electronic structures of these materials are well-suited for hot-exciton processes. Extension of this platform to a donor-acceptor architecture yields a hybridized local and charge-transfer (HLCT)-type emitter that achieves efficient exciton utilization and an external quantum efficiency of 9.91% with improved operational stability in deep-blue organic light-emitting diodes (OLEDs). When the designed compound BO-Phen-Pyr is employed as a sensitizer rather than solely as a direct emitter, a cyclic hot-exciton Dexter energy transfer (CH-DET) process is proposed, in which host-derived excitons are harvested and recirculated through BO-Phen-Pyrvia Dexter-mediated transfer channels before being funneled to the terminal emitter. The CH-DET pathway provides an additional exciton management channel that can utilize excitons otherwise lost in conventional triplet-triplet fusion (TTF)-based processes and mitigate triplet-related degradation pathways. Overall, this work establishes 1,4-oxaborine fusion as a general molecular design principle for transforming weakly emissive PAHs into efficient narrowband emitters. It also provides new insights into the development of color-pure organic optoelectronic materials.