Non-doped red-green-blue electroluminescence for fumaronitrile and fluorene bridge with pyrenyl or phenanthrylamino group

A red-emitting bis(4-(N-(1-pyrenyl)-3,5-dimethylphenylamino)phenyl)fumaronitrile (3) and a green-emitting 2,7-bis(N-1-pyrenyl-3,5-dimethylphenylamino)-9,9-diethylfluorene (4) were synthesized, while a red emissive bis(4-(N-(9-phenanthryl)-3,5-dimethylphenylamino)phenyl)fumaronitrile (5) and a blue 2,7-bis(N-9-phenanthryl-3,5-dimethylphenylamino)-9,9-diethylfluorene (6) were reported previously. The bulky and non-planar phenanthryl or pyrenyl amino substituent created steric torsional hindrance to restrict intermolecular aggregation and to promote high carrier mobility, thermal stability and luminous efficiency. The red non-doped devices for donor-π-acceptor 3 and 5 showed electroluminescent (EL) peaks at 668 and 652 nm with luminance (external quantum) efficiencies of 3.45 cd/A (6.89%), and 2.52 cd/A (3.74%), respectively. 4 exhibited EL peak at 500 nm with efficiency of 2.18 cd/A (0.81%). The device based on 6 was centered at 460 nm with efficiency of 1.86 cd/A (1.16%). The large planar pyrenyl group had stronger electron-donating ability than phenanthryl group, so the EL emissions from 3 and 4 redshifted compared with those from the homologous 5 and 6. EL efficiency was improved more effectively by pyrenyl unit than by phenanthryl unit. The prepared compounds were multifunctional materials with emitting and hole-transporting properties.