On-Surface Synthesis of Giant Conjugated Macrocycles

Isomerization of Organometallic Polymers on Ag(111): Revealing the Intermolecular Hydrogen Transfer Mechanism

Dehalogenation plays a crucial role in on-surface synthesis, but the bond-forming sites in dehalogenation occasionally differ from the original halogen-substituted sites, leading to unexpected products. Revealing its mechanism is essential for the atomically precise fabrication of low-dimensional nanomaterials, although it remains elusive. Herein, we report an isomerization of organometallic polymers derived from debromination on Ag(111) and elucidate the mechanism involving intermolecular hydrogen transfer via combining scanning tunneling microscopy, noncontact atomic force microscopy, and density functional theory calculations. At room temperature, the precursor 1,4-bis(3-bromothiophen-2-yl)benzene undergoes surface-assisted debromination on Ag(111), forming two organometallic polymers where the bond-forming sites correspond to the original debromination sites. Upon annealing to 393 K, the isomerization of organometallic polymers generates a linear organometallic polymer, where the bond-forming sites mismatched with the original debromination sites. Control experiments combined with theoretical calculations demonstrate that the unexpected isomerization proceeds through the dissociation of polymer chains into surface-stabilized diradical monomers or oligomers, intermolecular hydrogen transfer, and the final recombination of surface-stabilized radicals with Ag adatoms.

Two-Dimensional Nonbenzenoid Heteroacene Crystals Synthesized via In-Situ Embedding of Ladder Bipyrazinylenes on Au(111)

Precisely introducing topological defects is an important strategy in nanographene crystal engineering because defects can tune π-electronic structures and control molecular assemblies. The synergistic control of the synthesis and assembly of nanographenes by embedding the topological defects to afford two-dimensional (2D) crystals on surfaces is still a great challenge. By in-situ embedding ladder bipyrazinylene (LBPy) into acene, the narrowest nanographene with zigzag edges, we have achieved the precise preparation of 2D nonbenzenoid heteroacene crystals on Au(111). Through intramolecular electrocyclization of o-diisocyanides and Au adatom-directed [2+2] cycloaddition, the nonbenzenoid heteroacene products are produced with high chemoselectivity, and lead to the molecular 2D assembly via LBPy-derived interlocking hydrogen bonds. Using bond-resolved scanning tunneling microscopy, we determined the atomic structures of the nonbenzenoid heteroacene product and diverse organometallic intermediates. The tunneling spectroscopy measurements revealed the electronic structure of the nonbenzenoid heteroacene, which is supported by density functional theory (DFT) calculations. The observed distinct organometallic intermediates during progression annealing combined with DFT calculations demonstrated that LBPy formation proceeds via electrocyclization of o-diisocyanides, trapping of heteroarynes by Au adatoms, and stepwise elimination of Au adatoms.

Stepwise on-surface synthesis of nitrogen-doped porous carbon nanoribbons

Precise synthesis of carbon-based nanostructures with well-defined structural and chemical properties is of significance towards organic nanomaterials, but remains challenging. Herein, we report on a synthesis of nitrogen-doped porous carbon nanoribbons through a stepwise on-surface polymerization. Scanning tunneling microscopy revealed that the selectivity in molecular conformation, intermolecular debrominative aryl-aryl coupling and inter-chain dehydrogenative cross-coupling determined the well-defined topology and chemistry of the final products. Density functional theory calculations predict that the ribbons are semiconductors, and the band gap can be tuned by the width of the ribbons.

Current-Density Calculations on Zn-Porphyrin40 Nanorings

Two porphyrinoid nanorings have been studied computationally. They were built by linking 40 Zn-porphyrin units with butadiyne bridges. The molecular structures belonging to the D40h point group were fully optimized with the Turbomole program at the density functional theory (DFT) level using the B3LYP functional and the def2-SVP basis sets. The aromatic character was studied at the DFT level by calculating the magnetically induced current-density (MICD) susceptibility using the GIMIC program. The neutral molecules are globally non-aromatic with aromatic Zn-porphyrin units. Charged nanorings could not be studied because almost degenerate frontier orbitals led to vanishing optical gaps for the cations. Since DFT calculations of the MICD are computationally expensive, we also calculated the MICD using three pseudo-π models. Appropriate pseudo-π models were constructed by removing the outer hydrogen atoms and replacing all carbon and nitrogen atoms with hydrogen atoms. The central Zn atom was either replaced with a beryllium atom or with two inner hydrogen atoms. Calculations with the computationally inexpensive pseudo-π models yielded qualitatively the same magnetic response as obtained in the all-electron calculations.

Synthesis, nanostructuring and in silico studies of a new imine bond containing a macroheterocycle as a promising PBP-2a non-β-lactam inhibitor

This study is devoted to the synthesis of a 40-membered macroheterocycle with its further nanostructuring by magnetite nanoparticles. The mentioned macroheterocycle was synthesized by the [2+2] cyclocondensation of the oxygen-containing diamine with an aromatic dialdehyde in a non-catalytic medium and with no work-up procedure. The structure of the obtained macroheterocycle was studied by 1H and 13C nuclear magnetic resonance spectroscopy and matrix-assisted laser desorption/ionization-time of flight mass spectrometry. Furthermore, the nanosupramolecular complex of macroheterocycles with magnetite nanoparticles was obtained and investigated by Fourier-transform infrared and ultraviolet-visible spectroscopy methods. Shifts in the infrared spectra of the nanosupramolecular complex indicate the interaction through metal-aromatic ring non-covalent bonding. The shift is also observed for the C-O-C stretching band of ether bonds. The loading rate of macroheterocycles on magnetite nanoparticles was 18.6%. The morphology of the ensemble was studied by transmission electron microscopy, which confirmed the synthesis of nanospherical particles with a diameter range of 10-20 nm. Powder X-ray diffraction analysis showed patterns of cubic Fe3O4 nanoparticles with a crystallite size equal to 9.1 nm. The macroheterocycle and its nanosupramolecular complex were tested against Klebsiella pneumoniae, Pseudomonas aeruginosa and Staphylococcus aureus. The results have shown that the created complex has shown 64 times better activity against Staphylococcus aureus in comparison with the individual macroheterocycle and 32 times better activity in comparison with the pristine antibiotic Ampicillin as a control. In addition, computational analysis of the macroheterocycle was performed at the B3LYP/6-31G level in water. Molecular docking analyses for the macroheterocycle revealed Penicillin-binding protein PBP2a (5M18) from the transpeptidase family as a target protein in Staphylococcus aureus.

High-Yield Production of Quantum Corrals in a Surface Reconstruction Pattern

The power of surface chemistry to create atomically precise nanoarchitectures offers intriguing opportunities to advance the field of quantum technology. Strategies for building artificial electronic lattices by individually positioning atoms or molecules result in precisely tailored structures but lack structural robustness. Here, taking the advantage of strong bonding of Br atoms on noble metal surfaces, we report the production of stable quantum corrals by dehalogenation of hexabromobenzene molecules on a preheated Au(111) surface. The byproducts, Br adatoms, are confined within a new surface reconstruction pattern and aggregate into nanopores with an average size of 3.7 ± 0.1 nm, which create atomic orbital-like quantum resonance states inside each corral due to the interference of scattered electron waves. Remarkably, the atomic orbitals can be hybridized into molecular-like orbitals with distinct bonding and antibonding states. Our study opens up an avenue to fabricate quantum structures with high yield and superior robustness.

On-surface synthesis and spontaneous segregation of conjugated tetraphenylethylene macrocycles

Creating conjugated macrocycles has attracted extensive research interest because their unique chemical and physical properties, such as conformational flexibility, intrinsic inner cavities and aromaticity/antiaromaticity, make these systems appealing building blocks for functional supramolecular materials. Here, we report the synthesis of four-, six- and eight-membered tetraphenylethylene (TPE)-based macrocycles on Ag(111) via on-surface Ullmann coupling reactions. The as-synthesized macrocycles are spontaneously segregated on the surface and self-assemble as large-area two-dimensional mono-component supramolecular crystals, as characterized by scanning tunneling microscopy (STM). We propose that the synthesis benefits from the conformational flexibility of the TPE backbone in distinctive multi-step reaction pathways. This study opens up opportunities for exploring the photophysical properties of TPE-based macrocycles.

Theoretical modeling of the metal-organic precursors of anthracene-based covalent networks on surfaces

Surface-assisted fabrication of molecular network architectures has been a promising route to low-dimensional materials with unique physicochemical properties and functionalities. One versatile way in this field is the Ullmann coupling reaction of halogenated organic monomers on catalytically active metallic surfaces. In this work, using the coarse grained Monte Carlo simulations, we studied the on-surface self-assembly of metal-organic precursors preceding the covalent Ullman-type linkage of tetrahalogenated anthracene building blocks. To that end a series of positional isomers was examined and classified with respect to their ability of creation of extended network structures. Our simulations focused on the identification of basic types of self-assembly scenarios distinguishing enantiopure and racemic systems and producing periodic and aperiodic networks. The calculations carried out for selected tectons demonstrated wide possibilities of controlling porosity (e.g. pore size, shape, periodicity, chirality, heterogeneity) of the networks by suitable functionalization of the monomeric unit. The findings reported here can be helpful in rational designing of 2D polymeric networks with predefined structures and properties.