Bipolar Hosts Based on a Rigid 9,10-Dihydroanthracene Scaffold for Full-Color Electrophosphorescent Devices

Two bipolar hosts, CzDPO and CzDOxa, comprising a hole-transporting carbazole and an electron-transporting diphenyl phosphine oxide or oxadiazole with a saturated linker (9,10-dihydroanthracene) have been synthesized and characterized. The saturated linker limited the effective extension of pi conjugation, leading to high triplet energies (E-T=2.97-2.98 eV). The diastereomers with a rigid configuration provided an amorphous thin film with high thermal (T-d=415-444 degrees C) and morphological stability (T-g=188-224 degrees C). The high triplet energies and bipolar carrier transport characteristics (ambipolariy) of CzDPO and CzDOxa can facilitate exothermic energy transfer to the dopants and balance carrier injection/transport in the emission layers. As a result, they were utilized as universal hosts for various phosphorescent OLEDs (from blue to red), showing average external quantum efficiencies (eta(ext)=8.2-13.1%) and low efficiency roll-off. In addition, we also fabricated dual-emitter white organic light-emitting diodes with a co-doped single emissive layer. WOLED hosted by CzDOxa exhibited satisfactory device efficiencies (14.4%, 25.7 cdA(-1), 27lmW(-1)) with highly stable chromaticity (CIEx=0.26-0.28 and CIEy=0.38) at brightnesses from 560 to 15200 cd m(-2).