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-kernel, 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. The metal-ion complex is an ionic compound and has counter ions for balancing the charges of the metal ion which are capable of migrating within the electroluminescent device when the electroluminescent device is biased.