Endowing imidazole derivatives with thermally activated delayed fluorescence and aggregation-induced emission properties for highly efficient non-doped organic light-emitting diodes

The development and enrichment of high-performance organic fluorophores that simultaneously possess thermally activated delayed fluorescence (TADF) and aggregation-induced emission (AIE) properties is going pursued but remains a great challenge due to severe exciton quenching. Herein, a systematical investigation on imidazole moiety has successfully given rise to a series of highly efficient imidazole-based TADF-AIE luminogens for the first time. The attachment of two cyano functionalities on imidazole moiety can significantly increase the electron-withdrawing ability, so as to realize TADF emissions with small singlet-triplet energy gaps (Delta E-ST) values. Meanwhile, the installation of a steric hindrance group at N1 position of imidazole moiety can twist the geometry between imidazole and phenyl bridge, thus transforming imidazole derivative from an aggregation-caused quenching emitter into an AIE luminogen. Consequently, the non-doped organic light-emitting diodes (OLEDs) utilizing these TADF-AIE luminogens as emitters exhibit outstanding sky-blue and green emissions, with external quantum efficiency (EQE) as high as 20.0% and low efficiency roll-off (EQE at 1000 cd m(-2), 16.1%). These values represent the state-of-the-art performance for all imidazole-based OLED devices, which illustrates the significant potential of imidazole derivatives in assembling high-performance OLEDs.