Assembling Surface Molecular Sierpiński Triangle Fractals via K⁺-Invoked Electrostatic Interaction

Abstract

Molecular Sierpinśki triangles (STs), a family of elegant and well-known fractals, can be prepared on surfaces with atomic precision. Up to date, several kinds of intermolecular interactions such as hydrogen bond, halogen bond, coordination, and even covalent bond have been employed to construct molecular STs on metal surfaces. Herein a series of defect-free molecular STs have been fabricated via electrostatic attraction between potassium cations and electronically polarized chlorine atoms in 4,4″dichloro-1,1′:3′,1″-terphenyl (DCTP) molecules on Cu(111) and Ag(111). The electrostatic interaction is confirmed both experimentally by scanning tunneling microscopy and theoretically by density functional theory calculations. These findings illustrate that electrostatic interaction can serve as an efficient driving force to construct molecular fractals, which enriches our toolbox for the bottom-up fabrication of complex functional supramolecular nanostructures.

Separation of Halogen Atoms by Sodium from Dehalogenative Reactions on a Au(111) Surface

“…The corresponding network structure was thus tentatively superimposed on the zoomed-in STM image (Figure b), showing good agreement with the local part of the network. Moreover, the electrostatic potential map of the typical H 3 Na 3 motif (Figure d) shows that the Na atoms are positively charged, while negative potential regions exist around the C–Br bond axes, which rationalizes the electrostatic interactions between Na atoms and the surrounding Br substituents at the side position and accords well with a recent report regarding the interaction between K and three Cl substituents …”

“…In addition, the relative positions of three H-motifs in the Na-interlinked metal–organic clusters are not exactly the same, indicating different interaction modes between Na atoms and H-motifs. Based on the typical features and previous reports, , the involvement of excess Na in the assembled structure was proposed, and the corresponding DFT calculations on the structural models and STM simulations were performed (Figure S3). Accordingly, these bright dots at the junctions could be attributed to three, four, or even more Na atoms interacting with Br substituents of H-motifs in different interaction modes.…”

Toward Molecular Fractals on Surfaces: Designing Covalent Structures with the Monte Carlo Simulation Method

“…The only difference was the relative in-plane rotation/shift of the aggregates with respect to the main lattice directions induced by the mismatch of the overlayer and the substrate. The crowning example here is the theoretical discovery of the STs in the metal–organic system comprising terphenyl linkers and trivalent metal atoms, which was later validated experimentally by numerous research groups ,, (very recently using electrostatic interactions) and which stimulated further intense studies on the creation of deterministic-like molecular fractals on surfaces. ,− With this achievement in mind, we believe that the results of the present work will be useful in designing and fabricating persistent molecular fractals with tailorable architectures.…”

Predicting Molecular Self-Assembly on Metal Surfaces Using Graph Neural Networks Based on Experimental Data Sets

“…Due to its widespread importance, molecular self-assembly has received vast attention in the past decades. Molecular self-assemblies at solid surfaces could produce large-scale surface nanostructures. − And properties of molecular thin films, such as the optical absorbance and electrical conductivity, are dependent on the structures of molecules upon adsorption on a substrate. − Generally speaking, the self-assembled patterns are decided by the intrinsic properties of the molecules and environments, i.e., the balance of the adsorbate–adsorbate and adsorbate–surface interactions for molecular self-assemblies on surfaces. − Due to the complexity that arises from different aspects including the different functional groups of molecules, the size/shape of the molecular backbone, their adsorption geometries, as well as the different metal substrates, predicting the self-assembled structures remains an enormous challenge. − Meanwhile, constructing surface-supported supramolecular nanostructures through traditional trial-and-error methods relies on repeated preparations and experimental characterizations with advanced characterization tools, such as scanning probe microscopy (SPM), − which are typically time-consuming and costly.…”