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

Abstract

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 ⟨11̅0⟩ 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.