Monomolecular films of phthalocyanines: formation, characterization, and expelling by alkanethiols

Adsorption of aluminum-2,3-naphthalocyanine (Al-PC) onto gold (111) substrate from the pure and mixed (with alkanethiols) solutions of the target molecules in ethanol was studied. The resulting films were characterized by X-ray photoelectron spectroscopy and near-edge X-ray absorption fine structure spectroscopy. The adsorption from the pure solution resulted in formation of an Al-PC monolayer composed of the strongly inclined molecules. However, a presence of only one molar percent of a thiolated compound (alkanethiol) in the primary solution led to the complete expelling of the Al-PC molecules from the substrate and formation of a one-component alkylthiolate monolayer. The results indicate that an equilibrium formation of mixed monolayers of rodlike thiolated molecules and relatively large planar-geometry molecules, whose interaction with the metal surface is mainly provided by the pi-electron system, is difficult to achieve or is in most cases even impossible under equilibrium conditions and requires an introduction of additional anchor moieties (e.g., thiols) into these molecules, as has been demonstrated by successful coadsorption of hexadecanethiol and thiolated tetraphenylporphyrin.