Adsorption of Fumaramide [2]Rotaxane and Its Components on a Solid Substrate: A Coverage-Dependent Study

The coverage-dependent adsorption on Au(111) of a fumaramide [2]rotaxane and its components, a benzylic
amide macrocycle and a fumaramide thread, is studied using high-resolution electron energy loss spectroscopy
(HREELS). Up to monolayer coverage, the relative intensity of out-of-plane to in-plane phenyl ring vibrational
modes indicates that the macrocycle adopts an orientation with the phenyl rings largely parallel to the surface.
The formation of a chemisorption bond is evidenced by the presence of a Au−O stretching vibration. In
contrast, the thread shows no evidence of chemisorption or a preferential orientation. The introduction of the
thread into the macrocycle partly disrupts the film order so that the resulting chemisorbed rotaxane shows
intermediate behavior with a preferential orientation up to 0.5 ML coverage. A decrease in film order and the
absence of a preferred molecular orientation is observed for all three molecules at multilayer coverages. The
spectral differences are addressed by molecular dynamics simulations in terms of the mobility of the phenyls
of the three molecules on Au(111).