Pyrazoloquinoline derivatives as efficient blue electroluminescent materials

A series of 6-substituted-3-methyl-1-phenyl-4-(4-methoxyphenyl)-1H-pyrazolo[3,4-b]quinolines, MeOPAQ-X (X = t-Bu, OMe, H, F, Cl, Br), were synthesized and assessed as potential emitters in electroluminescent (EL) devices. All derivatives emitted in the blue region with an emission lambda (max) ranging from 448 nm to 460 nm and a quantum yield between 0.55 and 0.20. EL devices with a configuration of ITO/NPB/CBP/TPBI:MeOPAQ-X/TPBI/Mg:Ag were fabricated, where ITO, NPB, CBP, TPBI and Mg:Ag are indium tin oxide, 4,4'-bis[N-(1-naphthyl)-N-phenylamino]biphenyl, 4,4'-dicarbazolyl-1,1'-biphenyl, 2,2',2 "-(benzene-1,3,5-triyl)tris[1-phenyl-1H-benzimidazole] and magnesium : silver alloy (similar to 10 : 1) respectively. Light emission from the dopant was observed. An external quantum efficiency around 3% could be obtained for all substituted derivatives. In particular, brightness around 13 000 cd m(-2) was achieved for the device based on MeOPAQ-H. The performances were comparable to the best available materials in the blue organic light-emitting diodes.