Efficient non-doped blue organic light-emitting diodes: donor–acceptor type host materials

Abstract

The new blue light emitting materials, (E)-4′-(1-(4-(2-(1-(naphthalen-1-yl)-1H-phenanthro[9,10-d]imidazol-2-yl)vinyl)phenyl)-1H-phenanthro[9,10-d]imidazol-2-yl)-N,N-diphenyl-[1,1′]-biphenyl-4-amine (NPI-PITPA), (E)-4′-(1-(4-(2-(1-(4-methylnaphthalen-1-yl)-1H-phenanthro[9,10-d]imidazol-2-yl)vinyl)phenyl)-1H-phenanthro[9,10-d]imidazol-2-yl)-N,N-diphenyl-[1,1′]-biphenyl-4-amine (MeNPI-PITPA) and (E)-4′-(1-(4-(2-(1-(4-methoxynaphthalen-1-yl)-1H-phenanthro[9,10-d]imidazol-2-yl)vinyl)phenyl)-1H-phenanthro[9,10-d]imidazol-2-yl)-N,N-diphenyl-[1,1′]-biphenyl-4-amine (OMeNPI-PITPA) with dual charge transport properties have been synthesized and characterised. These compounds exhibit excellent thermal properties with very high glass-transition temperature and thus are favourable to form thin films under thermal evaporation for non-doped organic light-emitting diodes (OLEDs). The non-doped blue device based on OMeNPI-PITPA show maximum efficiencies (η_ex 4.90%; η_c 5.90 cd A⁻¹; η_p 5.10 lm W⁻¹) at low turn-on voltage and the device performances show that the phenanthroimidazole unit is a tunable building block for carrier injection properties and that they also can be used as hosts for green phosphorescent OLEDs.