Ordered Self-assembled Monolayers of β-dicarbonyl Derivatives Studied by STM

The adsorption of four β-dicarbonyl derivatives on highly oriented pyrolytic graphite (HOPG) surface was studied by scanning tunneling microscopy (STM) in an ambient environment. All the molecules include a π-conjugated part and alkyl chains in their chemical structures. The molecules were dissolved in toluene solvent and a drop of the solution was deposited on HOPG to form self-assembled adlayers. The characteristic stripe-like structure in the self-assembled monolayers (SAMs) on the high-resolution STM images of the compounds was observed. Different molecular structures led to different SAMs. It was found that noncovalent interactions such as hydrogen bonds and dipole-dipole interactions played an important role in the formation of different SAMs.