Structural Phase Transitions of Molecular Self-Assembly Driven by Nonbonded Metal Adatoms

Abstract

The involvement of metal atoms in molecular assemblies has enriched the structural and functional diversity of two-dimensional supramolecular networks, where metal atoms are incorporated into the architecture via coordination or ionic bonding. Here we present a temperature-variable study of the self-assembly of the 1,3,5-tribromobenzene (TriBB) molecule on Cu(111) that reveals the involvement of nonbonded adatoms in the molecular matrix. By means of scanning tunneling microscopy and noncontact atomic force microscopy, we demonstrate the molecular-level details of a phase transition of TriBB assembly from the close-packed to porous honeycomb structures at 78 K. This is an unexpected transformation because the close-packed phase is thermodynamically favored in view of its higher molecular density and more intermolecular bonds as compared to the honeycomb lattice. A comprehensive density functional theory calculation suggests that Cu adatoms should be involved in the formation of the honeycomb network, where the Cu adatoms help stabilize the molecular assembly via enhanced van der Waals interactions between TriBB molecules and the underlying substrate. Both calculation and experimental results suggest no chemical bonding or direct charge transfer between the adatoms and the molecules, thus the electronic characteristics of the Cu adatoms trapped in the molecular confinement are close to the intrinsic ones on a clean metal surface and different from those in the traditional coordination-bonded framework. The nonbonded metal adatoms embedded self-assemblies may complement the metal–organic coordination system and can be used to tailor the chemical reactivity and electronic properties of supramolecular structures.

On-Surface Self-Assembled Structural Transformation Induced by Schiff Base Reaction and Hydrogen bonds

“…It is necessary to note the balance is not immutable, and a series of elements will influence the self-assembled nanostructures, for instance, molecular concentration, light irradiation, temperature, solvent polarity, and so on. ,− Under some special circumstances, the self-assembled molecular structures could be transformed much more easily, such as the on-surface reaction. , In addition, the nanostructures formed by on-surface reaction are more thermodynamically and chemically stable and undergo the breakage and reformation of the covalent bonds. , During the on-surface reaction process, new molecules would be produced in situ and form new self-assembled architectures. , Thus, plentiful efforts have been made to investigate the on-surface synthesis of chemical molecules during these years, for example, the Schiff-based reaction, − Glaser reaction, − Ullmann coupling reaction, − photochemical reaction, , Knoevenagel reaction, and so forth . With the help of on-surface reactions, various self-assembled covalent structures have been successfully constructed on the 2D substrate. ,,− Furthermore, the intermediate products of the reaction are capable of being clearly detected by the actual-time and in situ STM characterization, which helps to elucidate the reaction principles of the molecular nanoarchitectures on the surface.…”

On-Surface Reaction of 1,4-Dibromo-2,5-Diiodobenzene on Au(111) and Ag(100)

“…As for molecules of halogen-substituted monophenyl rings, most of the studies so far are focused on on-surface reactions of molecular precursors substituted by same halogens and on Cu(111) and Cu(110) substrates but studies on multi-halogen-substituted precursors with heterogeneous halogens or on other catalytically active metal substrates are still lacking. Ordered self-assembled phases of monomers, organometallic intermediates, and covalent C–C bonded 1D chains or 2D frameworks have been observed after depositing the Br-substituted benzene molecules with different substitution numbers and positions at low temperature, annealing to RT, and further annealing, respectively. − Several superstructures of iodobenzene were found near saturation coverage on Cu(111) at 55 K and before long, diiodobenzene was reported to form molecular wires on Cu(110) after annealing to 500 K as well as deiodinated trimers after deposition onto Cu(111) through Ullmann coupling. It is worth noting that hexabromobenzene behaves quite differently on Au(111) and Ag(111).…”

Concentration–modulated global organizational chirality at the liquid/solid interface

“…12,13 When enantiomers are applied to the surface simultaneously, the presence of a small imbalance in the enantiomeric ratio can alter the adsorption system in favour of a single handedness. 14,15 As is known, the outcome of the self-assembling process relies on a series of factors, 16,17 including temperature, 18,19 electric eld, 20 magnetic eld 21 and the nature of the solvent. 22 Notably, the concentration of the assembled molecules has a striking inuence on the formation of self-assembled architectures as well.…”