Combining high-resolution scanning tunnelling microscopy and first-principles simulations to identify halogen bonding

Area of Science:

• Surface Science
• Supramolecular Chemistry
• Nanoscience

Background:

• Scanning Tunneling Microscopy (STM) is crucial for studying on-surface molecular self-assembly.
• Standard STM has limitations in fully elucidating complex supramolecular structures, particularly intermolecular interactions.

Purpose of the Study:

• To investigate the intermolecular interactions governing the self-assembly of a brominated polycyclic aromatic molecule on Au(111).
• To demonstrate an advanced STM approach for resolving detailed molecular structures and interactions.

Main Methods:

• High-resolution Scanning Tunneling Microscopy (STM) using a CO-functionalized tip.
• Density Functional Theory (DFT) calculations.
• Electron Density Topology Analysis.

Main Results:

• Standard STM was insufficient to determine intermolecular interactions.
• High-resolution STM with a CO-tip clearly identified atomic positions and revealed halogen bonding as the dominant interaction.
• DFT calculations supported stronger halogen bonding over hydrogen bonding.
• Electron density analysis confirmed characteristic features of halogen bonding.

Conclusions:

• Halogen bonding, not hydrogen bonding, governs the studied molecular assemblies.
• High-resolution STM with functionalized tips is a powerful tool for solving complex 2D supramolecular structures.
• This methodology is predicted to become increasingly important in molecular nanoscience.