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By using pyridine and diphenylphosphine oxide (DPPO) as dual n-type units, two novel bipolar hosts, namely (5-(3,5-di(9 H -carbazol-9-yl)phenyl)pyridin-3-yl)diphenylphosphine oxide ( m -PyPOmCP), and (6-(3,5-di(9 H -carbazol-9-yl)phenyl)pyridin-3-yl)diphenylphosphine oxide ( p -PyPOmCP) are developed for blue and green phosphorescent organic light-emitting diodes (PhOLEDs). Direct linking of the dual n-type units not only pulls the LUMOs down, but also keeps the HOMO levels shallow, and leads to high triplet energies (2.78-2.86 eV) and small singlet-triplet energy differences (0.23-0.35 eV). Blue and green PhOLEDs are fabricated using FIrpic and Ir(ppy) 3 as dopants in the hosts. A low turn-on voltage of 2.6 V is achieved for the green PhOLEDs. The m -PyPOmCP hosted blue PhOLED achieves a high current efficiency of 55.6 cd A -1 (corresponding to a maximum external quantum efficiency of 25.3% and a power efficiency of 43.6 lm W -1 ). The p -PyPOmCP hosted green PhOLED exhibits an efficiency of 98.2 cd A -1 (28.2% and 102.8 lm W -1 ). These data are among the best values for blue and green PhOLEDs reported so far. These "dual n-type units" hosts show much better performance than their DPPO-free analogue, clearly proving that the direct linking of DPPO and pyridine as dual n-type units is an effective molecular design strategy for host materials for use in high-performance PhOLEDs.

chemical science

Dual n-type units including pyridine and diphenylphosphine oxide: effective design strategy of host materials for high-performance organic light-emitting diodes