One-step synthesized novel spiro[fluorene-9,9'-xanthene]-based materials as highly efficient blue phosphorescent hosts in organic light-emitting devices

We synthesized a series of novel spiro[fluorene-9,9'-xanthene] (SFX)-based host materials via a one-step palladium-catalyzed cross-coupling reaction. These materials have high triple energy levels and high yield, and thus can be used as hosts for blue phosphors. Blue phosphorescent organic light-emitting devices (PHOLEDs) with a bis(3,5-difluoro-2-(2-pyridyl)phenyl-(2-carboxypyri-dyl)iridium(III) (FIrpic) emission were fabricated. Furthermore, we applied cohosts composed of one of the new synthesized materials and the hole transport material di-[4-(N,N-ditolyl-amino)-phenyl]cyclohexane (TAPC) to the blue PHOLEDs to successfully acquire efficient blue emissions. The SFX-based material provided efficient energy transfer while TAPC improved the mobility of the cohost as well as reduced the working voltage. Maximum current efficiencies of 22.56 and 25.93 cd·A^-1 and the maximum brightnesses of 6421 and 6196 cd·m^-2 were obtained for the PHOLEDs with TAPC: 2-(9-phenyl-fluoren-9-yl)spiro[fluorene-9,9'-xanthene] (PF-SFX) and TAPC: 2-(9-(4-(octyloxy)-phenyl)- 9H-fluoren-9-yl)spiro[fluorene-9,9'-xanthene] (C8OPF-SFX) cohosts, respectively. The experimental results obtained for the four SFX-based host materials were enough to declare that SFX is an effective main unit that can be used to build efficient host materials for blue phosphors containing only C, H, and O basic elements.