High solid-state fluorescent 9,9-bis(4-(diphenylamino) phenyl) fluorene-pyrenes as hole-transporting-free blue emitters for efficient solution-processed electroluminescent devices

The development of light-emitting conjugated materials (LEMs) with multiple functions not only improves photo and electronic properties to attain efficient and robust device electroluminescence (EL) performance, but also enhances the film-forming ability to manufacture large-area film via solution processing technology. Herein, new multi-functional blue LEMs (PY1 and PY2) bearing either 9,9-bis(4-diphenylaminophenyl)fluorene or 7,9,9-tris (4-diphenylaminophenyl)fluorene substituted at 1,3,6,8-positions of pyrene were designed, synthesized, and characterized as solution-processable hole-transporting-free blue emitters for simple structured solution processed organic light-emitting diodes (OLEDs). Both molecules adopted highly bulky molecular structures. They exhibited good quality thin films by spin-coating, stable blue emissions with high fluorescence emission efficiencies (64-71%), shallow HOMO levels (-5.31 to-5.38 eV), decent hole mobilities (2.31-5.05 x 10-6 cm2 V1s- 1),and high thermal stability, and effectively applied as non-doped emissive layers in the OLEDs. Especially, PY2-based OLED showed a bright blue emission with superior EL performance (brightness of 26415 cd m- 2, turn-on voltage (Von) of 2.8 V, external quantum efficiency (EQEmax) of 4.19%, and luminance efficiency (LEmax) of 10.53 cd A-1). This outstanding EL performance of the non-doped solution-processed blue OLED could be ascribed to the effective molecular design, and this work presented a new strategy for constructing useful blue emitters based on pyrene.