Electroluminescent device

An electroluminescent device includes a first electrode, a second electrode and, dispersed therebetween, an electroluminescent layer comprising a first and a second electroluminescent compound capable of emitting light of a first and a second color respectively, the first color being different form the second color. The electroluminescent device is capable of reversibly emitting light having predominantly the first color when biased at a low voltage in a first direction and light having predominantly the second color when biased at a low voltage in a second direction opposite to the first direction. The first electroluminescent compound may be an electroluminescent polymer or low-molecular weight conjugated electroluminescent compound. The second electroluminescent compound is a metal-ion complex, typically mono-kernel or bi-kemel, having one or more ligands. At least one of said one or more ligands is substituted with a conjugated moiety, such as an oligo-phenylenevinylene or an oligo-phenylene derivative. T