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

Anisotropic functionalized platelets: percolation, porosity and network properties

Anisotropic functionalized platelets are able to model the assembly behaviour of molecular systems in two dimensions thanks to the unique combination of steric and bonding constraints. The assembly scenarios can vary from open to close-packed crystals, finite clusters and chains, according to the features of the imposed constraints. In this work, we focus on the assembly of equilibrium networks. These networks can be seen as disordered, porous monolayers and can be of interest for instance in nano-filtration and optical applications. We investigate the formation and properties of two dimensional networks from shape anisotropic colloids functionalized with four patches. We characterize the connectivity properties, the typical local bonding motives, as well as the geometric features of the emerging networks for a large variety of different systems. Our results show that networks of shape anisotropic colloids assemble into highly versatile network topologies, that may be utilized for applications at the nanoscale.

Phase Transitions of Naphthalene-2,3-carbonitride Steered by Solvent Effects and Metal Ion Concentration Variation

The delicate regulation of structural phase transition can provide advanced approaches for fabricating desired and well-organized nanoarchitectures on surfaces. Introduction of metal ions into pure organic systems can facilitate the phase transition from hydrogen-bonded structures to metal-organic structures by coordinating with organic molecules. However, it remains a challenge to attain a phase transition dominated by variable metal coordination configurations through adjustment of the metal ion concentration. Herein, we report the phase transitions of naphthalene-2,3-carbonitride (2,3-DCN) molecules on highly oriented pyrolytic graphite (HOPG) under varying solvents and Cu2+ ion concentrations. By integrating data from scanning tunneling microscopy imaging and density functional theory calculations, it is demonstrated that phase transitions of 2,3-DCN occur through forming diverse coordination configurations where Cu2+ ions can coordinate with 2,3-DCN and 1-nonanoic acid or Cl- ions to form different ligand components with a coordination number of 4 when varying the molar ratios of 2,3-DCN to Cu2+ ion in the 1-nonanoic acid solvent. However, in the case of 1-heptanoic acid as a solvent, the self-assembly structure of 2,3-DCN only changes via the alteration of hydrogen bonding sites and Cu2+ ions do not coordinate with 2,3-DCN molecules. These findings provide valuable insights into the coordination behavior of metal ions in different solvents.

Coronene guest molecule selectivity in host templates formed by hydrogen bonding and van der Waals forces at liquid/solid interfaces

COR guest molecules are selectively adsorbed in the hexagonal cavities in both H6PDB and H6PAB self-assembled systems and preferentially adsorbed in the H6PAB host template in the H6PAB/HPB system.

Analysis of Guest Adsorption on Crystal Surfaces Based on the Fragment Molecular Orbital Method

For gaining insights into interactions in periodic systems, an analysis is developed based on the fragment molecular orbital method combined with periodic boundary conditions. The adsorption energy is decomposed into guest and surface polarization and deformation energy, guest-surface and guest-guest interactions, and the vibrational free energy. The analysis is applied to the adsorption of guest molecules to Ih (001) ice surface. The cooperativity effects result in a non-linear change in the adsorption energy with coverage due to many-body effects. The role of dispersion is found to be dominant for guests with long hydrophobic tails. A rule is proposed relating the length of the alkyl tail with the formation of the guest layer. The computed binding enthalpies are in good agreement with experimental values. For high coverage, adsorbed molecules can form an ordered layer known as self-assembled monolayer.

The self-assembly and pyridine regulation of a hydrogen-bonded dimeric building block formed by a low-symmetric aromatic carboxylic acid

The supramolecular self-assembly behavior of a low-symmetric aromatic carboxylic acid molecule (H₅BHB) and its co-assembly behavior with a series of pyridine molecules (BPD, BPDYB and TPDYB) were studied at the heptanoic acid/HOPG liquid-solid interface. Scanning tunneling microscopy (STM) observations revealed that H₅BHB molecules tend to form dimeric building blocks which then assemble into a close-packed structure. BPD, BPDYB and TPDYB pyridine molecules were all able to form a stable two-component co-assembled structure with the H₅BHB molecule, and in these co-assembled structures, the H₅BHB molecule still takes the form of a dimer. It was found that the pyridine molecules were able to regulate the self-assembly structure of the H₅BHB molecule, and the molecular arrangement of the co-assembly structures varies with the shape of the pyridine molecules. Based on the analysis of the STM results and density functional theory (DFT) calculations, the formation mechanism of the assembled structures was revealed.

Odd-Even Effect on Supramolecular Co-Assemblies: Control over the Two-Dimensional Self-Assemblies of a Fluorenone Derivative with Asymmetrically Substituted Alkyl Chains

The precise control of two-dimensional supramolecular co-assemblies presents a research topic related to advance nanotechnology. Here, we report a scanning tunneling microscopy (STM) study of the mixture behavior of three fluorenone derivatives at the liquid-solid interface. The target molecule is F-C₁₂C₁₃ whose structure bears asymmetrical alkyls, whereas the regulating molecules, either F-C₁₂C₁₂ or F-C₁₃C₁₃, are structurally symmetric. By STM imaging of systematic mixtures with various volumes among the sample solutions, we found that the mixing ratio mainly determined the binary outcomes. Compared with F-C₁₂C₁₂, F-C₁₃C₁₃ shows a stronger ability to dominate the patterning, explained by the larger binding and adsorption energies calculated by the force field simulations. Moreover, the odd-even effect exists in the system. Overall, we acquired knowledge about the regulating ability of bi-component supramolecular assembling, especially for structurally asymmetric molecular systems.

Progress in the self-assembly of porphyrin derivatives on surfaces: STM reveals

The latest progress in the assembly of porphyrin derivatives on solid surfaces.