Preparation, reactivity and controlled release of SAMs of calix[4,6]arenes and calix[6]arene-based rotaxanes and pseudorotaxanes formed on polycrystalline Cu

Abstract

Specific and reversible binding of guest molecules from a solution to a surface pre-treated with host molecules is a recent and active field of research. Self-assembled monolayers may result from supramolecular interactions, adding distinct functionalities to the surface. In this frame, the first compared study is given here of the anchoring on the technologically relevant Cu surface of calix[4]arene receptors and calix[6]arene-based rotaxanes and pseudorotaxanes. These molecules, which belong to the most representative classes of compounds in supramolecular chemistry, have been chosen for their synthetic accessibility and versatility, which make them useful building blocks for the synthesis of new advanced supramolecular structures. Covalent functionalisation of calix[4,6]arenes on Cu was reached via a dip-coating procedure, optimizing the various synthetic aspects in order to obtain good coverages and copper passivation. Molecular adhesion has been demonstrated by the presence and relative quantitation of XPS signals from specific elements in the molecules. We have successfully tested the combination of different functionalities by producing a mixed film, prepared by ligand exchange of calix[4]arene with undecanethiol. The availability of the calix[4]arene cavity to reversibly host further species after anchoring on Cu has been demonstrated by a sequence of uptake and release cycles with pyridinium salts. Rotaxane and pseudorotaxane species, composed of a calix[6]arene wheel functionalized with N-phenylurea groups on the upper rim, and a viologen-containing axle, have been anchored on Cuvia the SH-termination of the axle. XPS demonstrated the successful self-assembly of fully threaded rotaxanes and pseudorotaxanes from their solutions and the controlled release upon biasing of full rotaxanes and of the pseudorotaxane wheel.