Scanning tunnelling microscopy (STM) is commonly used to identify on-surface molecular self-assembled structures. However, its limited ability to reveal only the overall shape of molecules and their relative positions is not always enough to fully solve a supramolecular structure. Here, we analyse the assembly of a brominated polycyclic aromatic molecule on Au(111) and demonstrate that standard STM measurements cannot conclusively establish the nature of the intermolecular interactions. By performing high-resolution STM with a COfunctionalised tip, we clearly identify the location of rings and halogen atoms, determining that halogen bonding governs the assemblies. This is supported by density functional theory calculations that predict a stronger interaction energy for halogen rather than hydrogen bonding and by an electron density topology analysis that identifies characteristic features of halogen bonding. A similar approach should be able to solve many complex 2D supramolecular structures, and we predict its increasing use in molecular nanoscience at surfaces.

Electrospray deposition and STM as a new analytical technique to sequence conjugated polymers and reveal polymerization defects.

Transfer capillaries are the preferred means to transport ions, generated by electrospray ionization, from ambient conditions to vacuum. During the transfer of ions through the narrow, long tubes into vacuum, substantial losses are typical. However, recently it was demonstrated that these losses can be avoided altogether. To understand the experimental observation and provide a general model for the ion transport, here, we investigate the ion transport through capillaries by numerical simulation of interacting ions. The simulation encompasses all relevant factors, such as space charge, diffusion, gas flow, and heating. Special attention is paid to the influence of the gas flow on the transmission and especially the change imposed by heating. The gas flow is modeled by a one-dimensional gas dynamics description. A large number of ions are treated as point particles in this gas flow. This allows to investigate the influence of the capillary heating on the gas flow and by this on the ion transport. The results are compared with experimental findings. Graphical Abstract ᅟ.

Although hydrogen bonds have long been established as a highly effective intermolecular interaction for controlling the formation of self-assembled monolayers, the potential utility of the closely related halogen bonds has only recently emerged. The synergistic use of both halogen and hydrogen bonds provides a unique, multitiered strategy toward controlling the morphology of self-assembled structures. However, the interplay between these two interactions within monolayer systems has been little studied. Here, we have systematically investigated this interplay in self-assembled monolayers formed at the solid–liquid interface, with a specific attention on determining the structural relevance of the two interactions in the formation of 2D supramolecular structures. A single molecule that can simultaneously act as both a halogen and a hydrogen bond donor was paired with molecules that are effective acceptors for both of these interactions. The bimolecular networks that result from these pairings were studied by using scanning tunneling microscopy coupled with density functional theory calculations. Additional measurements on similar networks formed by using structural analogues in which halogen-bonding interactions are no longer possible give significant insight into the structure-determining role of these interactions. We find that in some monolayer systems the halogen bonds serve no significant structure-determining role, and the assembly is dominated by hydrogen bonding; however, in other systems, effective cooperation between the two interactions is observed. This study gives clear insight into the synergistic and competitive balance between halogen and hydrogen bonds in self-assembled monolayers. This information is expected to be of considerable value for the future design of monolayer systems using both halogen and hydrogen bonds.

Fluorination transforms a simple carboxylic acid into a highly effective building block for the formation of bimolecular monolayers.

Fluorination turns a prototypical diphenol into an effective hydrogen-bond-donating building block for the formation of 2D phenol–pyridine cocrystals.