Molecular Design of Non-doped OLEDs Based on a Twisted Heptagonal Acceptor: A Delicate Balance between Rigidity and Rotatability.

The development of efficient non-doped organic light-emitting diodes (OLEDs) is highly desired but very challenging because of a severe aggregation-caused quenching effect. Herein, we present a heptagonal diimide acceptor (BPI), which can restrict excessive intramolecular rotation and inhibit close intermolecular π-π stacking due to well-balanced rigidity and rotatability of heptagonal structure. The BPI-based luminogen (DMAC-BPI) shows significant aggregation-induced delayed florescence with an extremely high photoluminescence quantum yield (95.8 %) of the neat film, and the corresponding non-doped OLEDs exhibit outstanding electroluminescence performance with maximum external quantum efficiency as high as 24.7 % and remarkably low efficiency roll-off as low as 1.0 % at 1000 cd m-2 , which represents the state-of-the-art performance for non-doped OLEDs. In addition, the synthetic route to DMAC-BPI is greatly streamlined and simplified through oxidative Ar-H/Ar-H homo-coupling reaction.