A Deep-Blue Electroluminescent Device Based on a Coumarin Derivative

The design and synthesis is reported of 7-(9H-carbazol-9-yl)-4-methylcoumarin (Cz-Cm), comprising a carbazole donor moiety and a 4-methylcoumarin acceptor unit, for use in a blue organic light-emitting diode. A detailed solid state, theoretical and spectroscopic study was performed to understand the structure-property relationships. The material exhibits deep-blue emission and high photoluminescence quantum yield both in solution and in a doped matrix. A deep-blue electroluminescence emission at 430 nm, a maximum brightness of 292 cd m^-2 and an external quantum efficiency of 0.4 % was achieved with a device configured as follows: ITO/NPD (30 nm)/TCTA (20 nm)/CzSi(10 nm)/10 wt % Cz-Cm:DPEPO (10 nm)/TPBI (30 nm)/LiF (1 nm)/Al [ITO=indium tin oxide, NPD=N,N'-di(1-naphthyl)-N,N'-diphenyl-(1,1'-biphenyl)-4,4'-diamine, TCTA=tris(4-carbazoyl-9-ylphenyl)amine, CzSi=9-(4-tert-butylphenyl)-3,6-bis(triphenylsilyl)-9H-carbazole, DPEPO=bis[2-(diphenylphosphino)phenyl]ether oxide, TPBI=1,3,5-tris(N-phenylbenzimidazol-2-yl)benzene].