Porous Network Structure of Octacyano-Metal-Free Phthalocyanine on the Basal Plane of Highly Oriented Pyrolytic Graphite

Abstract

We report the formation of a porous network structure of octacyno-metal-free phthalocyanine (H2Pc(CN)8) on a highly oriented pyrolytic graphite surface. The porous structure shows a quadratic packing with one void per unit cell and an average void area of 3 nm2 due to the interaction of cyano groups. The nature of the molecule−molecule interaction was established by a tip-induced molecular rearrangement and force-field simulations. Typical point (filling) defects in the porous structure suggest that this molecular layer might be used as a template for other organic molecules. Regions with high point defect densities are seen to form a close-packed phase, which is found to be developing in small islands. A modified MM2 force field was employed on different quadratic unit cells in which the azimuthal orientation and the intermolecular distance of the molecular lattice were changed to find the minimum-energy structure. Both porous network structure and close-packed phases are found in the calculations, corresponding to two minimum-energy structures in the force-field calculations. The adsorption geometries of molecules in the porous and the close-packed phases are understood by simulating them on the graphene sheet and from the calculated scanning tunneling microscope images.