Dimeric SFX host materials for red, green and blue phosphorescent organic light-emitting devices

Two novel spiro[fluorene-9,9′-xanthene]-based derivatives 23′ODSFX and 3′3′ODSFX, without possessing conventional hole- or electron-transporting units, have been synthesized by a simple reaction procedure and been demonstrated to be host materials for efficient and low-voltage blue, green and red phosphorescent organic light-emitting devices (PHOLEDs). They showed good thermal stability with high glass transition temperatures (T_g) at 210 °C for 23′ODSFX and 138 °C for 3′3′ODSFX. Compared with SFX-based devices, the performance of 23′ODSFX-based devices increased nearly 20 times, although the difference of HOMO/LUMO levels and triplet levels between dimeric SFX and SFX was very small. The blue PHOLEDs based on 23′ODSFX and 3′3′ODSFX exhibited the same low turn-on voltage of ∼2.6 V, and maximum current efficiency (CE) of 21.7/12.9 cd cd A^-1, power efficiency (PE) of 19.5/11.5 lm W^-1, and external quantum efficiency (EQE) of 11.9%/7.2%, respectively. It was evident that the different position linkage in host materials was closely relative to the device performance.