Grafting of benzylic amide macrocycles onto acid-terminated self-assembled monolayers studied by XPS, RAIRS, and contact angle measurements

The grafting of benzylic amide macrocycles, the basic units of more complex mechanically interlocked architectures such as catenanes and rotaxanes, was performed via the functionalization of an acid-terminated self-assembled monolayer (SAM) of 11-mercaptoundecanoic acid (11-MUA). Both chemical and physical adsorption were investigated using macrocycles containing either a reactive hydroxyl functionality or an exo-pyridyl moiety, with characterization of the systems using X-ray photoelectron spectroscopy (XPS), contact angle measurements, and reflection absorption infrared spectroscopy (RAIRS). By comparing theoretical values with experimental data, it was found that up to 40% of the acid groups on the SAM surface were modified by the macrocycles and that the macrocycle coverage can be controlled by varying the reaction time. Stability tests demonstrated that the prepared films are stable in air, under ultrasound treatment and against chemical substitution. RAIRS measurements suggested a tilted orientation of the macrocycle with respect to the plane of the SAM surface.