Highly Luminescent Monolayers Prepared by Molecular Layer Deposition

A general avenue for the controlled preparation of conformal and highly luminescent monolayers of metal chelate complexes is presented, among them tris(8-hydroxyquinolinato) aluminium (Alq(3)) and bis(8-hydroxyquinoline)zinc (Znq(2)). Alq(3) is an extremely important model compound for organic electronic applications - it has been the electron transporter and luminescent material in the first efficient hetero-structure organic light emitting diode (OLED). The controlled formation of Alq(3) or Znq(2) monolayers is achieved by functionalization of the substrate with amino groups which serve as initial docking sites for trimethyl aluminum (TMA) or diethyl zinc (DEZ) molecules which datively bind to the amine. Subsequent exposure to 8-hydroxyquinoline (8-HQ) results in the self-limiting formation of highly luminescent monolayers on arbitrary surfaces, e.g. curved 3D objects or highly porous silica aerogels. The growth mechanism is studied by in-situ quartz crystal microbalance and ex-situ by highly sensitive (time-resolved) optical absorption/emission spectroscopy and photoelectron spectroscopy.