A bulky pyridinylfluorene-fuctionalizing approach to synthesize diarylfluorene-based bipolar host materials for efficient red, green, blue and white electrophosphorescent devices

Abstract

By incorporating electron-transporting pyridine and hole-transporting fluorene moieties into a nonplanar 3-dimensional molecule, via the sp³-hybridized carbon linkage by Friedel–Crafts reaction, three novel donor–acceptor (p–n) bipolar host materials 9-(pyridin-2-yl)-3-(9-(pyridin-2-yl)-fluoren-9-yl)-carbazole (CzPy-PyFM), 3,6-bis(9-(pyridine-2-yl)-fluoren-9-yl)-9-(pyridin-2-yl)-carbazole (CzPy-DPyFM) and 5,5′′-bis(9-(pyridin-2-yl)-fluoren-9-yl-)-2,2′:5′,2′′-terthiophene (T₃DPyFM) have been synthesized successfully. These pyridinylfluorene end-capped materials with large steric hindrance have been applied as efficient universal hosts for blue, green and red PhOLEDs. The blue, green, and red PhOLEDs hosted by highly thermally stable CzPy-PyFM exhibit the maximum external quantum efficiencies (EQEs) of 10.49%, 11.04%, and 6.50%, respectively. On this basis, the single-emissive-layer three-color and all-phosphor CzPy-PyFM-based white PhOLEDs have been fabricated, which acquire a maximum current efficiency of 10.4 cd A⁻¹, a power efficiency of 10.2 lm W⁻¹ and an EQE of 5.58%. This is the first example of the diarylfluorenes as universal hosts for full-color RGB PhOLEDs as well as white PhOLEDs.