Dipyrazolopyridine derivatives as bright blue electroluminescent materials

Very bright blue organic light emitting diodes were fabricated using highly fluorescent dipyrazolopyridine derivatives, 4-(4-substituted phenyl)-1,7-diphenyl-3,5-dimethyl-1,7dihydrodipyrazolo[3,4-b,4',3'-e]pyridine (PAP-X, X=CN, Ph, and OMe), as emitter by doping the dye in an electron-transporting host, 2,2',2 "-(1,3,5-benzenetriyl)tris-[1-phenyl-1H-benzimidazole] (TPBI). Two hole-transporting layers, 4,4'-bis[N-(1-naphthyl-1-)-N-phenyl-amino]-biphenyl (NPB) and 4,4'-dicarbazolyl-1,1'-biphenyl (CBP) were used to achieve the emission from PAP-X. The devices with a general configuration of indium tin oxide/NPB/CBP/TPBI:PAP(2%)/Mg:Ag showed a bright blue emission. The PAP-CN-based device is exceptionally good, with a brightness of 11 200 cd/m(2) at 14.2 V and the peak external quantum efficiency of 3.2%. The efficiency is the highest for the blue emission. (C) 2000 American Institute of Physics. [S0003-6951(00)01833-7].