Multifunctional pyridine styrylphenanthroimidazoles: electron transport materials for blue FOLEDs with low efficiency roll-off and hosts for PHOLEDs with low turn-on voltage

Abstract

We have reported pyridine styrylphenanthroimidazole derivatives, SPPI-C₂Py, SPPI-N₁Py and SPPI-C₂N₁Py, as efficient electron transport materials (ETMs) for blue fluorescent OLEDs (FOLEDs) and host materials for phosphorescent organic light emitting diodes (PHOLEDs). The optical and carrier transport abilities of pyridine styrylphenanthroimidazoles have been analyzed in terms of the linkage position as well as number of pyridine fragments. Devices with SPPI-C₂Py, SPPI-N₁Py and SPPI-C₂N₁Py as ETMs exhibit a maximum current efficiency (CE) of 14.28, 9.63 and 16.93 cd A⁻¹, power efficiency (PE) of 9.32, 4.74 and 11.23 lm W⁻¹ and external quantum efficiency (EQE) of 7.93, 5.50 and 8.68% relative to the widely used ETM BPhen (CE – 11.69 cd A⁻¹; PE – 5.01 lm W⁻¹; EQE – 5.89%). The blue PHOLEDs using SPPI-C₂Py, SPPI-N₁Py and SPPI-C₂N₁Py as hosts exhibit a CE of 34.32, 30.65 and 43.23 cd A⁻¹, PE of 32.09, 28.32 and 40.54 lm W⁻¹ and EQE of 18.56, 16.32 and 22.43%. The red PHOLEDs using SPPI-C₂N₁Py as a host exhibit a maximum CE of 25.78 cd A⁻¹, PE of 22.68 lm W⁻¹ and EQE of 18.56%. The yellow PHOLEDs using SPPI-C₂N₁Py as a host exhibit a maximum CE of 70.53 cd A⁻¹, PE of 40.86 lm W⁻¹ and EQE of 25.89%, respectively. These findings demonstrated that the new born pyridine styrylphenanthroimidazoles can be employed as potential ETMs for blue FOLEDs and hosts for blue, red and yellow PHOLEDs.