Electronic structure of tris(8-hydroxyquinoline) aluminum thin films in the pristine and reduced states

The electronic structure of tris(8-hydroxyquinoline) aluminum (Alq(3)) has been studied in the pristine molecular solid state as well as upon interact ion (doping) with potassium and lithium. We discuss the results of a joint theoretical and experimental investigation, based on a combination of x-ray and ultraviolet photoelectron spectroscopies with quantum-chemical calcula tions at the density functional theory level. Upon doping, each electron tr ansferred from an alkali metal atom is stored on one of the three ligands o f the Alq(3) molecule, resulting in a new spectral feature (peak) in the va lence band that evolves uniformly when going from a doping level of one to three metal atoms per Alq(3) molecule. (C) 1999 American Institute of Physi cs. [S0021-9606(99)50628-4].