Synthesis of spiro[fluorene-9,9′-xanthene] derivatives and their application as hole-transporting materials for organic light-emitting devices

A series of hole-transporting molecules based on spiro(fluorene-9,9′-xanthene) were designed and synthesized by a copper-catalyzed modified Ullmann reaction. These compounds have very high-lying HOMO levels (∼5.0 eV), which are beneficial for the hole-injection from ITO anode. The double-layer EL devices using DPA-SFXMe and DPA-SFXBu as hole-transporting layers exhibit lower turn-on voltage and higher efficiency compared with those of a typical NPB-based device. The DPA-SFXBu-based device exhibits high maximum luminescence of 21,712 cd/m2, and its power efficiency can reach a value of 2.31 lm/W, which is nearly 90% higher than that of a similar NPB-based device.