New donor–π–acceptor AIEgens: Influence of π bridge on luminescence properties and electroluminescence application

Abstract

Aggregation-induced emission (AIE) offers a solution to harvest strong solid-state fluorescence, which is crucial to achieving efficient organic light-emitting diodes (OLEDs). In this study, two novel AIE luminogens (AIEgens) were designed by integrating the advantages of triphenylamine (TPA) and phenanthroimidazole (PI), which exhibited excellent electron-donating ability of TPA and bipolar characteristics and suitable carrier transporting ability of PI. The two structural units were connected by a π bridge of tris/tetrastyrene group with a different number of benzene rings. Intra-/inter-molecular charge transfer can be obtained by adjusting the conjugation of the π bridge, and the AIE activity is also manipulated accordingly. The dilute solutions of TPE-TPAPPI present concentration- and polarity-dependent emission, demonstrating emission Adjustability by controlling the ratio of intramolecular and intermolecular charge transfer. It is found that intermolecular charge transfer dominates in film state. A non-doped OLED based on TPE-TPAPPI shows a maximum external quantum efficiency (EQE) of 4.01% with a low turn-on voltage of 3.2 V. The efficiency roll-off is only 4.75% even at a high brightness of 1000 cd m−2, demonstrating the superiority of our AIEgens in OLED application.