Highly efficient non-doped blue electroluminescent materials for organic light-emitting devices

We have synthesized the new blue-light-emitting materials 4,4′-bis(1-(naphthalen-1-yl)-1H-phenanthro[9,10]imidazole-2-yl)-1,1′-biphenyl (NPIP), 4,4′-bis(4-methylnaphthalen-1-yl)-1H-phenanthro[9,10]imidazole-2-yl)-1,1′-biphenyl(MeNPIP) and 4,4′-bis(4-methoxynaphthalen-1-yl)-1H-phenanthro[9,10]imidazole-2-yl-1,1′-biphenyl(MeONPIP) through a two-step procedure using inexpensive catalysts. These compounds showed excellent thermal properties with a very high glass-transition temperature of 195–201 °C due to their rigid molecular backbones and they emit intense blue light in both solution and film. A device fabricated with MeONPIP shows maximum efficiencies (η_ex 6.92%; η_c −7.80 cd A⁻¹; η_p 6.10 lm W⁻¹) with a low turn-on voltage and the performances of the device suggest that the phenanthroimidazole unit is an excellent building block for tuning carrier injection properties as well as for blue emission.