Sharp green electroluminescence from 1H-pyrazolo[3,4-b]quinoline-based light-emitting diodes

A multilayer organic light-emitting diode was fabricated using a fluorescent compound $\text{{6-N,N-}\mathrm{diethylamino-1-methyl-3-phenyl}\text{-1H-}\mathrm{pyrazolo}\text{[3,4-b]}\mathrm{quinoline}\}$ $({\mathrm{PAQ–NEt}}_{\mathrm{2}})$ doped into the hole-transporting layer of NPB ${\text{{4,4}}^{\prime }-\mathrm{bis}\text{[N-(1-}\mathrm{naphthyl}\text{-1-)-N-}\mathrm{phenyl-amino}\mathrm{]-}\mathrm{biphenyl}\mathrm{\},}$ with the TPBI ${\text{{2,2}}^{\prime }{\text{,2}}^{″}\text{-(1,3,5-}\mathrm{phenylene})\mathrm{tris}\text{[1-}\mathrm{phenyl}\text{-1H-}\mathrm{benzimidazole}\mathrm{]\}}$ as an electrontransporting material. At 16% ${\mathrm{PAQ–NEt}}_{\mathrm{2}}$ doping concentration, the device gave a sharp, bright, and efficient green electroluminescence (EL) peaked at around 530 nm. The full width at half maximum of the EL is 60 nm, which is 60% of the green emission from typical NPB/AlQ [where $\mathrm{AlQ=tris(8-hydroxyquinoline) aluminum}]$ device. For the same concentration, a maximum luminance of $\text{37\hspace{0.05em}000\hspace{0.05em}}{\mathrm{cd/m}}^{\mathrm{2}}$ was obtained at 10.0 V and the maximum power, luminescence, and external quantum efficiencies were obtained 4.2 lm/W, 6.0 cd/A, and 1.6%, respectively, at 5.0 V.