Optimizing the conjugation between N,N′-dicarbazolyl-3, 5-benzene and triphenylphosphine oxide as bipolar hybrids for highly efficient blue and single emissive layer white phosphorescent OLEDs

Two bipolar host materials, mCPpPO and mCPmPO have been synthesized by Ni(II)/Zn-catalyzed cross-coupling of diphenylphosphine oxide and corresponding aryl bromide. The photophysical properties, HOMO/LUMO orbital distribution and triplet levels of these host materials are investigated and optimized by tuning the linking modes between electron acceptor triphenylphosphine oxide and electron donor N,N'-dicarbazolyl-3,5-benzene (mCP). When mCP is linked to the meta-position of benzene of triphenylphosphine oxide, the hybrid (mCPmPO) shows much higher steric hinderance than the para-position linked analogue (mCPpPO) so that it possesses a higher triplet energy. Equipped with the bipolar transport properties, mCPmPO-based blue PhOLED doped FIrpic shows a maximum current efficiency (eta(c,max)) of 40.0 cd/A, a maximum power efficiency (eta(p,max)) of 39.7 lm/W, corresponding the maximum external quantum efficiency (eta(EQE,max)) of 20.3%, and the current efficiency still maintain to 34.8 cd/A even at 1000 cd/m(2). Based on the optimized triplet energy level, the single emission layer white PhOLED hosted by mCPmPO shows eta(c,max), eta(p,max) and eta(EQE,max) of 46.9 cd/A, 39.7 lm/W and 17.6%, respectively. (C) 2013 Elsevier B. V. All rights reserved.