Comparison study of two isomers of benzimidazole for effective blue OLEDs

Two isomers of benzimidazoles, N,N-diphenyl-4′-(1-phenyl-1H-benzo[d] imidazol-2-yl)-[1,1′-biphenyl]-4-amine (TPABBI) and N,N-diphenyl-4′-(1-phenyl-1H-benzo[d]imidazol-2-yl)-[1,1′-biphenyl]-3-amine (m-TPABBI), were developed for blue OLEDs. Their photophysical properties, density functional theory calculations, and electroluminescent performance were investigated. Obviously, TPABBI exhibited good performance with the efficiencies of 3.56 cd A−1, 3.11 lm W−1, and 4.23%, which could be attributed to the simulational enhancement of charge transfer and local excited states. The corresponding m-TPABBI showed relatively low efficiencies of 1.27 cd A−1, 0.88 lm W−1, and 1.02%, while the m-TPABBI exhibited better color purity than that of TPABBI. Our results provided a useful strategy for the generation of non-doped deep blue electroluminescent materials.