By incorporating the pyridine ring to the different position of rigid phenanthroimidazole skeleton, three new pyridine-containing phenanthroimidazole derivatives, 1-phenyl-2-(4-(pyridin-3-yl)phenyl)-1H-phenanthro[9,10-d]imidazole(CPI-p3Py), 2-phenyl-1-(4-(pyridin-3-yl)phenyl)-1H-phenanthro[9,10-d]imidazole(NPI-p3Py) and 1,2-bis(4-(pyridin-3-yl)phenyl)-1H-phenanthro[9,10-d]imidazole(CNPI-p3Py), were designed and synthesized as electron-transport materials (ETMs). Their photophysical properties, energy levels and electron mobilities can be readily regulated through changing the connecting position. Through optimizing electron mobility and energy levels trade-offs, CNPI-p3Py exhibits not only lower-lying HOMO/LUMO energy levels, but also relatively higher electron mobility around 10 -3 cm 2 V -1 s -1 , which is 2-fold greater than that of the widely used material BPhen. More interesting, the blue fluorescent OLEDs with CPI-p3Py or CNPI-p3Py as an electron-transporting layer (ETL) exhibited superior performance compared to that using Bphen, remarkably lowering the driving voltage and improving efficiencies. In particular, the device with CNPI-p3Py as an ETL showed a maximum current efficiency of 15.17 cd A -1 , a maximum power efficiency of 10.65 lm W -1 , a maximum external quantum efficiency (EQE) of 7.75% and low efficiency roll-off even at an illumination-relevant luminance of 10,000 cd m -2 by the efficient utilization of the up-conversion of a triplet excited state, which are among the most efficient ETMs and proposes a new strategy for the molecular design of high-performance ETMs.
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