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. Crown Copyright (C) 2011 Published by Elsevier B.V. All rights reserved.