Adsorption of a benzylic amide macrocycle on a solid substrate: XPS and HREELS characterization of thin films grown on Au(111)

Thin films of a benzylic amide macrocycle, the common component of a wide class of mechanically interlocked molecules, are prepared by vapor deposition on Au(111). The films are characterized by monochromated X-ray photoelectron spectroscopy (XPS) and high resolution electron energy loss spectroscopy (HREELS). The relative amounts of carbon, nitrogen, and oxygen are consistent with the formation of intact molecular species. At monolayer coverage, the relative intensity of out-of-plane to in-plane phenyl ring vibrational modes indicates that the macrocycle adopts a nearly flat-lying conformation. The formation of a chemisorption bond is evidenced by the presence of a Au-O stretching vibration and a low binding energy component in the O 1s core level region assigned to interfacial bonding. A decrease in film order and the absence of a preferred molecular orientation is observed at higher coverages. Computer modeling of the adsorption of the macrocycle on the surface rationalizes the experimental observations.