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

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 (T1) 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 T1 and separated frontier molecular orbitals. This work thus sheds light on the rational design of SFX-based bipolar hosts for more efficient PhOLEDs. [Display omitted] •New spiro bipolar hosts have been developed for green and red PhOLEDs.•Frontier energy levels can be tuned by different substitution patterns on the spiro core.•PhOLED device performances are impacted by structural variation of SFX-based hosts.