Novel heterofluorene-based hosts for highly efficient blue electrophosphorescence at low operating voltages

A novel concept for molecular design of blue host materials for phosphorescent OLEDs (PHOLEDs) by combining carbazole and heterofluorene via structurally mimicking 4,4′-N,N′-dicarbazole-biphenyl (CBP) was presented. The carbazole end-capped heterofluorenes (CzHFs) prepared accordingly in high yields, were found to be ideal hosts for blue PHOLEDs. At the brightness level of 1000 and 5000 cd m−2, the driving voltages are still lower than 4.5 V with the external quantum efficiencies retain as high as 18.1% and 16.8% respectively.

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► Rational design of host materials by mimicking 4,4′-N,N′-dicarbazole-biphenyl (CBP).
► Extraordinary device performance with low turn-on voltages and high efficiencies.
► At a brightness level of 5000 cd m−2, the external quantum efficiency remains 16.8%.
► The easily synthesized m-CzHFs have wide applications as host materials.