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

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.