Metal-Alq(3) Complexes: The Nature of the Chemical Bonding

Alq(3) (tris(8-hydroxyquinolino) aluminum) is the most widely used electroluminescent molecule in organic light-emitting devices. An urgent strong need exists currently to understand its chemistry and its reactivity, especially to those metals that constitute the cathodes commonly used. Complexes with single metal atoms are expected to form in metal-doped Alq(3) layers as well as at several stages of the functioning of the device. These, however, elude characterization via experiment only. The present study provides such a characterization by means of a series of calculations using density-functional theory with gradient-corrected functionals of complexes with Li, Al, and Ca. Very clear results emerge that allow us to understand the nature of the interaction of the organic with such metal atoms, and to identify the common as well as the metal-specific electronic and structural characteristics of each of them. Moreover, these calculations shed light onto the specific and non-trivial effects that the formation of these chemical species can have on the intrinsic properties of the organic material.