Surface grafting and reactivity of calixarene-based receptors and pseudorotaxanes on Si(100)

Abstract

The first report is given here on the anchoring on H–Si(100) of calix[4]arenes and calix[6]arene-based pseudorotaxanes, versatile building blocks for molecular devices. Covalent functionalization on Si was reached through a wet chemistry recipe, by making use of an extra-mild photochemical activation via visible light of CC terminated anchoring arms. Our approach largely preserves the integrity of the molecular substrate, also allowing for a full monolayer of pseudorotaxane to be formed on Si(100). Molecular adhesion has been demonstrated by the presence and quantitation of XPS signals from specific elements in the molecules. AFM measurements performed on Si(100)/calix[4]arenes have revealed structures 2.3 nm high, consistent with the length of the molecule. The availability of the calix[4]arene cavity to host further species after anchoring on Si has been demonstrated by the successful complexation reaction with Cs⁺ ions, resulting in a 1 ∶ 1 calix/Cs⁺ ratio, and with N-methyl pyridinium iodide. A pseudorotaxane species, composed of a calix[6]arene wheel derivatised with N-phenylureido groups on the upper rim and a viologen (4,4′-bipyridinium) containing axle, has been anchored on Si(100) via the CC termination of the axle. We demonstrated the self-assembling of this pseudorotaxane covalently bound by use of XPS.