A series of fluorenone-carbazole based regioisomers as bipolar host materials for efficient organic light emitting diodes

A series of fluorenone-carbazole based regioisomers (1–4) have been synthesized and applied as host materials for red OLEDs to investigate the effect of different connection configuration on the optoelectronic properties, charge transport capability and device performance. The optoelectronic properties, thermal stability, redox behaviors and charge transport characteristics of these four compounds were fully characterized. These four hosts demonstrated high thermal stability, bipolar charge transport properties and good EL performance. Although these four compounds demonstrated similar HOMO and LUMO energy levels, the twisted structure of 1 led to the smallest singlet-triplet energy gap, which could account in part for the observation of its better EL performance.