A novel neutral red derivative for applications in high-performance red-emitting electroluminescent devices

A new compound with intramolecular charge transfer (ICT) character-neutral red derivative (I)-was designed and synthesized. The new compound is strongly fluorescent in nonpolar and moderately polar solvents. Using this material as a dopant, we fabricated electroluminescent (EL) devices with a structure of indium tin oxide (ITO) coated glass/ N,N′-bis(1-naphthyl)-N,N′-diphenyl-1,1′-biphenyl- 4,4′-diamine (NPB) (60 nm)/tris(8-hydroxyquinolinato)aluminum (Alq₃):dopant (30 nm)/Alq₃ (20 nm)/Mg-Ag (200 nm). The device showed orange-to-red EL emission with good efficiency and high brightness. The device with a doping concentration of 1 wt % exhibited a high brightness of 18400 cd/m² at a driving voltage of 13 V, and the current efficiency is 5.2 cd/A at a current density of 20 mA/cm². An important feature of the device is its fairly constant current efficiency over a wide range of current density from 1 mA/cm² to as high as 500 mA/cm² at different doping concentrations. The current devices show obvious advantages over many reported red-emitting OLEDs, which show significant drops in efficiency as the current density and/or dopant concentration increases. The present red dopant is particularly suitable for passive-matrix display applications where a high excitation density is required.