Blue light-emitting diodes based on dipyrazolopyridine derivatives

A series of highly luminescent; dipyrazolopyridine (PAP) dyes were synthesi zed and assessed as light-emitting materials in electroluminescent devices. Multilayer devices were fabricated using these dyes along with a hole-tran sporting material, NPB (4,4'-bis[N-(1-naphthyl-1-)-N-phenyl-amino]-biphenyl ) and an electron-transporting material, AlQ (tris(8-hydroxyquinoline) alum inum), or TPBI (2,2',2"-(1,3,5-benzenetriyl)tris[1-phe benzimidazole]). Bot h ITO/NPB/PAP/AlQ/Mg:Ag and ITO/NPB/PAP/TPBI/Mg:Ag devices gave a bright bl ue or blue-green emission, depending on the substituent group in the parent PAP dye. The performance of these devices such as turn-on voltage, brightn ess, and efficiency as a function of the substituent is discussed.