Supramolecular Monolayers of Zinc Porphyrin Trimers on Graphite

Zinc porphyrin trimers have been deposited on highly oriented pyrolytic graphite (HOPG) from the liquid phase. By controlling the concentration of the solution and deposition parameters, we have prepared single molecular layers. The molecular monolayers, as characterized using both atomic force microscopy (AFM) and scanning tunneling microscopy (STM), are amorphous. The trimer molecules adopt a uniform adsorption orientation with the component porphyrin rings perpendicular to the substrate, giving rise to a monolayer film thickness of 1.7 ± 0.2 nm, which is characteristic of the height of the individual molecules. STM imaging of the molecular layers was conducted both in vacuum and in air, giving identical results. This type of molecular monolayer provides a useful platform for the study of surface and interface phenomena outside a vacuum system and is potentially useful for practical fabrication of molecular devices because of the simplicity of the sample preparation and the stability of the interface in ambient.