Borja Cirera

Synthesis of extended graphdiyne wires by vicinal surface templating.

Surface-assisted covalent synthesis currently evolves into an important approach for the fabrication of functional nanostructures at interfaces. Here, we employ scanning tunneling microscopy to investigate the homocoupling reaction of linear, terminal alkyne-functionalized polyphenylene building-blocks on noble metal surfaces under ultrahigh vacuum. On the flat Ag(111) surface, thermal activation triggers a variety of side-reactions resulting in irregularly branched polymeric networks. Upon alignment along the step-edges of the Ag(877) vicinal surface drastically improves the chemoselectivity of the linking process permitting the controlled synthesis of extended-graphdiyne wires with lengths reaching 30 nm. The ideal hydrocarbon scaffold is characterized by density functional theory as a 1D, direct band gap semiconductor material with both HOMO and LUMO-derived bands promisingly isolated within the electronic structure. The templating approach should be applicable to related organic precursors and different reaction schemes thus bears general promise for the engineering of novel low-dimensional carbon-based materials.

2 D Self‐Assembly and Catalytic Homo‐coupling of the Terminal Alkyne 1,4‐Bis(3,5‐diethynyl‐phenyl)butadiyne‐1,3 on Ag(111)

The covalent linking of terminal alkynes is a promising approach for the bottom‐up fabrication of novel, carbon‐rich or all‐carbon materials, which was recently extended towards interfacial architectures. Here we report the synthesis of a novel organic species (1,4‐bis(3,5‐diethynylphenyl)butadiyne‐1,3) and employ it to engineer self‐assembled supramolecular layers and covalent networks on the Ag(111) surface. Samples are prepared in‐situ under ultra‐high vacuum conditions and examined at the molecular level with scanning tunneling microscopy. After evaporating the two‐fold symmetric molecule onto the substrate at temperatures below 300 K and subsequent cooling to 5 K we find highly regular supramolecular phases commensurate with the underlying silver surface and stabilized mainly by weak, non‐covalent interactions originating from the terminal ethynyl moieties. Annealing at temperatures between 350 and 500 K triggers catalytic conversions with the pertaining covalent coupling reactions resulting in small aggregates or irregular polymeric networks. Our detailed analysis of the binding motifs demonstrates that two competing reaction pathways dominate the covalent linking processes. The first is the Glaser–Hay‐type homo‐coupling of two alkyne terminations leading to a linear butadiyne bridge. The second is the connection of a butadiyne group to a laterally attacking terminal alkyne, converting the attacked ethyne to ethene moieties, which presents a major obstacle for the production of regular networks.

Thermal selectivity of intermolecular versus intramolecular reactions on surfaces.

On-surface synthesis is a promising strategy for engineering heteroatomic covalent nanoarchitectures with prospects in electronics, optoelectronics and photovoltaics. Here we report the thermal tunability of reaction pathways of a molecular precursor in order to select intramolecular versus intermolecular reactions, yielding monomeric or polymeric phthalocyanine derivatives, respectively. Deposition of tetra-aza-porphyrin species bearing ethyl termini on Au(111) held at room temperature results in a close-packed assembly. Upon annealing from room temperature to 275 °C, the molecular precursors undergo a series of covalent reactions via their ethyl termini, giving rise to phthalocyanine tapes. However, deposition of the tetra-aza-porphyrin derivatives on Au(111) held at 300 °C results in the formation and self-assembly of monomeric phthalocyanines. A systematic scanning tunnelling microscopy study of reaction intermediates, combined with density functional calculations, suggests a [2+2] cycloaddition as responsible for the initial linkage between molecular precursors, whereas the monomeric reaction is rationalized as an electrocyclic ring closure.

Surface-Supported Robust 2D Lanthanide-Carboxylate Coordination Networks

Lanthanide-based metal-organic compounds and architectures are promising systems for sensing, heterogeneous catalysis, photoluminescence, and magnetism. Herein, the fabrication of interfacial 2D lanthanide-carboxylate networks is introduced. This study combines low- and variable-temperature scanning tunneling microscopy (STM) and X-ray photoemission spectroscopy (XPS) experiments, and density functional theory (DFT) calculations addressing their design and electronic properties. The bonding of ditopic linear linkers to Gd centers on a Cu(111) surface gives rise to extended nanoporous grids, comprising mononuclear nodes featuring eightfold lateral coordination. XPS and DFT elucidate the nature of the bond, indicating ionic characteristics, which is also manifest in appreciable thermal stability. This study introduces a new generation of robust low-dimensional metallosupramolecular systems incorporating the functionalities of the f-block elements.