Synthesis, properties, and OLED characteristics of 2,2′-bipyridine-based electron-transport materials: the synergistic effect of molecular shape anisotropy and a weak hydrogen-bonding network on molecular orientation

Abstract

To boost the performances of OLEDs, one of the most promising approaches from a materials chemistry viewpoint is the use of thin solid films with horizontal molecular orientations. In this work, we developed 2,2′-bipyridine-skeleton-based electron-transport materials (ETMs) end-capped with 3,5-dipyridylphenyl groups with the objective of preparing films with horizontal molecular orientations for use in high-performance organic light-emitting devices (OLEDs). These compounds afforded highly oriented films and were used in fac-tris(2-phenylpyridine)iridium(III)-based OLEDs as ETMs. The optimized device exhibited low operating voltages of 2.8 and 3.2 V at luminances of 100 and 1000 cd m⁻², respectively. At 1000 cd m⁻², this device exhibited a power efficiency of 74 lm W⁻¹ and an external quantum efficiency of 21%.