Low-Temperature Scanning Tunneling Microscopy Study of Self-Assembly of Molecular Dipoles on Surfaces

Abstract

Non-planar phthalocyanines with a permanent dipole were chosen as model systems to investigate both the construction of molecular dipole arrays and the substrate effects on the adsorption structures of dipolar Pcs on various substrates.It is found that 2D molecular dipole dot arrays can be fabricated on HOPG; while unidirectionally aligned molecular dipole arrays can be realized based on site-specific adsorption of VOPc at the elbow sites on Au(111) with O-down configuration. Dipole alignment dependent symmetry reduction has been observed in VOPc/ClAlPc on Cu(111) systems, which is due to the lifted degeneracy of the LUMO of Pc ligand. We focused on the STM experiments, and the results are also rationalized by theoretical calculations.