Sensitized electroluminescence on mesoporous oxide semiconductor films

Forward biasing of a mesoporous TiO2 (anatase) film whose surface is derivatized with a monolayer of the phosphonated ruthenium bipyridyl complex RuL(2)L' with L = 4,7-diphenyl-1,10-phenanthroline and L' = 2,2'-bipyridine-4,4'-diphosphonic acid produces electroluminescence in the presence of an electrolyte containing peroxodisulfate in dimethylformamide. Light emission arises from the MLCT excited state of the complex which is generated directly through interfacial electron transfer from the conduction band of the semiconductor to the pi* orbital of the oxidized Ru(III) state of RuL(2)L'. The nanocrystalline morphology of the oxide film used here as electron injection electrode plays an important role in enhancing the electroluminescence process.