Supramolecular Ordering and Reactions of a Chlorophenyl Porphyrin on Ag(111)

Surface-assisted Ullmann-type coupling reactions are a potential bottom-up approach for building tailored low-dimensional materials with novel physical and chemical properties. In this investigation combining scanning tunneling microscopy (STM), density functional theory (DFT), and X-ray photoelectron spectroscopy (XPS), we study the adsorption behavior, supramolecular ordering, and chemical and physical changes upon annealing of a 5,10,15,20-tetrakis(4-chlorophenyl) porphyrin (Cl4TPP) on the Ag(111) surface. At room temperature, well-ordered two-dimensional (2D) assemblies grow preferentially along the ?11¯ 0»directions, revealing the coexistence of two distinguishable porous and zigzag structures and lattice parameters. Our DFT calculations show that Cl4TPP adsorbs in the typical saddle-shape conformation on Ag(111) and that the coexistence of these two overlayers is due to translations between nearly isoenergetic adsorption sites. Furthermore, to self-polymerize the organic mesh via an on-surface Ullmann-type coupling reaction, we performed an STM and XPS study of the system upon annealing, following the chemical and structural modifications above room temperature. Under these conditions, we obtain a highly compact 2D framework composed of dechlorinated molecules.