A new family of bis-DCM based dopants for red OLEDs

We have synthesized a series of novel bis-DCM derivatives as candidate red dopants for use in organic light-emitting devices (OLEDs), by introducing various donor-substituted aryl rings. Compared to DCJTB (621 nm), the novel dopants (637-677 nm) showed more red-shifted emission in 1,2-dichloroethane. Using bis-DCMNEtOBu (7) as a dopant, we fabricated OLEDs with the configuration of ITO/4,4′,4″-tris(3-methylphenylammo)triphenylamine (m-MTDATA) (20 nm)/N,N′-bis(1-naphthyl)-diphenyl-1,1′-biphenyl-4,4′-diamine (NPB) (40 nm)/tris(8-quinolinolato)aluminium (Alq₃) : red dopant (35 nm, x wt%)/Alq₃ (35 nm) LiF/Al. The device with a doping concentration of 1.25 wt% showed pure red emission at λ_max = 654 nm (chromaticity coordinate: x = 0.67, y = 0.33) and a maximum brightness of 2500 cd m^-2. The chromaticity coordinates were almost independent of current density. Moreover, highly efficient red emission (x = 0.63, y = 0.36) was obtained in the 0.74 wt% doped device. The maximum external quantum efficiency was 4.46% at 7 V, the current efficiency was 3.43 cd A^-1, and the power efficiency was 1.64 Im W^-1. The highest brightness of 8300 cd m^-2 was obtained at 19.6 V.