Porphine Homocoupling on Au(111)

Abstract

The covalent coupling of porphine molecules on Au( 111) is studied by scanning probe microscopy experiments and density functional theory. At sufficient temperatures, dehydrogenative C−C coupling of the unfunctionalized molecules occurs directly on the surface. Characteristic dimer structures between individual porphine molecules are observed and assigned to various binding motifs that are distinguished by specific intermolecular connections. Different preparations show that the relative abundance of these motifs depends on the temperature of the gold sample during deposition and is explained by calculated free energies and kinetic aspects that are relevant during the linking process. Observations on the gold terraces are completed by studying polymerization at step edges, giving insight into their role during the covalent linking process.

On-Surface Synthesis of Rigid Benzenoid- and Nonbenzenoid-Coupled Porphyrin–Graphene Nanoribbon Hybrids

“…It is not entirely clear though if the short Por–GNRs synthesized by this hot deposition approach emerge from a sequential reaction of C–C coupling followed by cyclodehydrogenation or if they are assembled from naphthalene-fused porphyrin monomers whose radical sites were not yet passivated by hydrogen atoms produced in the dehydrogenation reaction. Passivated naphthalene-fused porphyrin monomers are unlikely to dehydrogenate and couple, as efficient dehydrogenative cyclization between planar porphyrins on Au(111) is reported only for temperatures larger than 300 °C. , …”

“…Therefore, they usually do not meet the criteria for efficient charge transport. Short doubly and triply fused porphyrin oligomers were synthesized by dehydrogenative porphine homocoupling on Ag(111) and Au(111), , but only recently, the synthesis of well-defined triply (β, meso ,β) linked porphyrin tapes containing up to 12 units has been achieved . Employing meso -substituted porphyrins, intramolecular cyclodehydrogenation can induce nonbenzenoid motifs (i.e., five-membered rings), which have been well documented for individual tectons − and porphyrins in coordination chains …”

Noble Metal Substrate Identity Effects on the Self-Assembly, Dynamics, and Dehydrocyclization Reaction of Octaethylporphyrin Molecules

“…This process has previously been observed to occur for free-base porphine molecules on a metal surface. 53,54 Overall, the strong interactions of OEP with the Cu(100) substrate were found to prohibit the self-assembly of larger supramolecular structures, as well as catalyze the dehydrocyclization reaction at 600 K where the potential products may include oligomer formation.…”

On-Surface Synthesis of Nonmetal Porphyrins

“…Porphyrin molecules play an important role in biological systems and are used in diverse technological and medical applications. − The characteristic porphyrin macrocycle can host most elements of the periodic table and can be further functionalized by peripheral substituents. − In a nano- and surface science scenario relying on an ultrahigh vacuum (UHV) environment, porphyrin complexes are extensively studied as building blocks for self-assembled molecular films, , two-dimensional metal–organic coordination networks, , and covalent architectures. − In this context, the on-surface synthesis of porphyrin complexes, and specifically the metalation of free-base (2H) species by intrinsic surface adatoms or deposited atoms, was shown to provide elegant routes to metalloporphyrin architectures with distinct chemical, physical, and structural properties. − In addition to the magnetic and electronic structure of the central atom, its size plays a relevant role in the properties of the resulting complex. While 3d metal ions are generally positioned in or near the macrocycle plane, larger elements such as lanthanides are displaced from the molecular center (e.g., allowing for the in situ formation of double- and multidecker assemblies , ).…”