Quinolyl functionalized spiro[fluorene-9,9'-xanthene] host materials with bipolar characteristics for green and red phosphorescent organic light-emitting diodes

摘要

Spiro[fluorene-9,9'-xanthene] (SFX) bipolar hosts bearing one, two and three quinolyl substituents, namely SFX-bPy, SFX-DbPy and SFX-TbPy, were designed and synthesized for phosphorescent organic light emitting diodes (PhOLEDs). The successive substitution of quinoline at 2', 2 and 7' positions of SFX results in reduced LUMO energy levels while leaving the HOMO energy levels nearly intact The impact of quinoline substitution in these SFX-based hosts on PhOLED performance was investigated in detail through green and red model devices. For the green emitting devices, the device based on SFX-bPy host showed better performance (23.6 cd A~(-1), 23.4 lm W~(-1), 6.3%) due to high triplet energy level (T_1) and balanced carriers-transporting ability. In contrast, for the red PhOLED devices, the device hosted by SFX-DbPy displayed higher performance (15.8 cd A~(-1),16.0 lm W~(-1), 9.1%), attributable to the well matched T_1 and separated frontier molecular orbitals. This work thus sheds light on the rational design of SFX-based bipolar hosts for more efficient PhOLEDs.