A Deep‐Blue Electroluminescent Device Based on a Coumarin Derivative

The design and synthesis is reported of 7‐(9 H ‐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)‐9 H ‐carbazole, DPEPO=bis[2‐(diphenylphosphino)phenyl]ether oxide, TPBI=1,3,5‐tris( N ‐phenylbenzimidazol‐2‐yl)benzene].