Dibenzophenazine‐Fused Heterocyclic Luminophores: Decoding High‐Performance Organic Light‐Emitting Diodes Based on Long‐Wavelength Exciplex

ABSTRACT Developing highly efficient long‐wavelength exciplexes remains a challenge due to the constraints of the energy gap law and severe non‐radiative loss. In this study, we report a rigid nitrogen‐rich donor, 3N, featuring the first fused framework constructed from two anti‐aromatic phenazine units. This unique architecture ensures 3N has good planarity and an exceptionally shallow highest occupied molecular orbital (HOMO) energy level of −4.88 eV. Meanwhile, the effective suppression of structural relaxation by its rigid scaffold contributes to a narrow emission at 456 nm. By pairing 3N with planar boron‐containing acceptors through strong intermolecular interactions, highly efficient exciplex emissions ranging from green to orange‐red were successfully achieved. Two representative exciplex systems reached outstanding photoluminescence quantum yields of 92% at 557 nm and 78% at 604 nm, respectively. Correspondingly, organic light‐emitting diodes based on these exciplexes delivered maximum external quantum efficiencies of 25.6% at 556 nm and 24.7% at 586 nm, respectively. To the best of our knowledge, these values rank among the highest performance metrics reported for long‐wavelength exciplexes. These results demonstrate that fusing multiple phenazine units could significantly raise the HOMO level and enhances structural rigidity, thereby enabling highly efficient long‐wavelength exciplex electroluminescence.