Extremely low-efficiency roll-off of phosphorescent organic light-emitting diodes at high brightness based on acridine heterocyclic derivatives

Three novel host materials, IpCm-PhBzAc (1,3-(4-(12,12-dimethylbenzofuro[3,2-b]acridin-7(12H)-yl)phenyl)-6-isopropyl-4H-chromen-4-one), DpAn-BzAc (2,10-(4-(12,12-dimethylbenzofuro[3,2-b]acridin-7(12H)-yl)phenyl)-10-phenylanthracen-9(10H)-one) and DpTrz-BphBzAc (3,7-(4′-(4,6-diphenyl-1,3,5-triazin-2-yl)-[1,1′-biphenyl]-4-yl)-12,12-dimethyl-7,12-dihydrobenzofuro[3,2-b]acridine) have been designed and synthesized, and their utilization as host materials for phosphorescent organic light-emitting diodes (PhOLEDs) has been investigated. We have fabricated PhOLEDs using green bis(2-phenylpyridine)iridium(iii) acetylacetonate as doped emitters and two hosting schemes, which are the single host system consisting of BzAc derivatives and the co-host system with 1,3-bis(carbazolyl)benzene. We found that the PhOLEDs with the co-host system of DpAn-BzAc and DpTrz-BphBzAc achieved CEs of 57.1 cd A⁻¹ and 53.0 cd A⁻¹, with corresponding efficiency roll-off of only 7.6% and 0.9%, respectively, from the maximum to the practical brightness of 5000 cd m⁻². Extremely reduced efficiency roll-off values for BzAc-based PhOLEDs were attributed to their superior thermal stability and excellent bipolar transport properties, and a small singlet-triplet energy gap also afforded efficient reverse intersystem crossing, thus reducing the triplet density of the host for PhOLEDs.