Adsorption of fumaramide [2]rotaxane and its components on a solid substrate: a coverage-dependent study

Area of Science:

• Surface Science
• Supramolecular Chemistry
• Materials Science

Background:

• Understanding molecular adsorption on surfaces is crucial for designing advanced materials.
• Rotaxanes, mechanically interlocked molecules, offer unique structural properties for surface assembly.

Purpose of the Study:

• To investigate the adsorption behavior of a fumaramide [2]rotaxane and its individual components (macrocycle and thread) on Au(111).
• To determine the molecular orientation and bonding modes during adsorption.
• To elucidate the impact of molecular structure on film order and surface interactions.

Main Methods:

• High-resolution electron energy loss spectroscopy (HREELS) to analyze vibrational modes and surface bonding.
• Coverage-dependent adsorption studies from submonolayer to multilayer regimes.
• Molecular dynamics simulations to complement experimental findings and explain mobility.

Main Results:

• The macrocycle component chemisorbs with phenyl rings oriented parallel to the Au(111) surface.
• The fumaramide thread shows no chemisorption or preferential orientation.
• The assembled rotaxane exhibits intermediate adsorption behavior, with disrupted film order compared to the macrocycle alone.
• Multilayer coverages lead to decreased film order and loss of preferred orientation for all molecules.

Conclusions:

• Chemisorption and preferential orientation are strongly influenced by molecular structure and assembly.
• The rotaxane's structure leads to a more disordered adsorption compared to its macrocycle component.
• Molecular dynamics confirm differences in phenyl ring mobility explain observed spectral variations.