New pyrene-based butterfly-shaped blue AIEgens: Synthesis, structure, aggregation-induced emission and their nondoped blue OLEDs

Developing the blue emitters with excellent electroluminescence (EL) performance is crucial for full-color displays and solid-state lighting. Based on the synthetic strategy for exploring highly efficient luminescent solids by constructing aggregation-induced emission (AIE) systems, two new pyrene-based butterfly-shaped blue AIEgens, Py(5,9)BTPE and Py(5,9)BTriPE, have been successfully designed and synthesized by integrating two tetra-phenylethylene (TPE) or triphenylethylene (TriPE) groups into pyrene ring. The adoption of the pyrene unit with a large optical bandgap, the use of the TPE or TriPE group with ME characteristic, the integration of the TPE or TriPE group into pyrene ring at 5,9-positions, and the highly twisted molecular conformations of present ME systems endow the two compounds with bright blue emission in the solid state. These foregoing features ensure that the new pyrene-based compounds can serve as excellent blue-emitting materials in OLEDs. A non-doped OLED based on Py(5,9)BTPE exhibited a sky-blue emission (V-on: 3.2 V) with a CIE coordinates of (0.19, 0.28), a maximum external quantum efficiency (EQE(max)) of 3.35%, a current efficiency (CE) of 6.51 cd A(-1) with a low efficiency roll-off that represents one of the highest value reported for sky-blue ME-based OLEDs. An analogous device with Py(5,9)BTriPE as an emitting layer displayed a pure-blue emission (CIE: 0.16, 0.17) with a moderate EQE(max) of 1.27% and a CE of 1.63 cd A(-1) with a low efficiency roll-off. Furthermore, the EL emissions of the two devices display almost no change with the increasing of the current density, indicating their good color stability.