Homogeneously mixed molecular assemblies of defined stoichiometry were created by adsorption of asymmetric, trifunctional ligands on gold and CuInSe2 (CISe). The ligands rely on cyclic disulfide groups for binding to the substrate and can in addition possess two different substituents, one polar substituent (p-cyanobenzoyl or anisoyl) and one long-chain, aliphatic residue (palmitoyl). Because the substituents are covalently connected, no phase segregation will occur upon surface binding. Adsorption of these ligands on conducting surfaces changed both the surface potential (because of the polar substituent) and hydrophobicity (because of the aliphatic residue). Larger changes of surface potential were obtained by adsorption of the symmetric, dipolar ligands than by adsorption of the asymmetric ligands, and larger changes occurred on gold than on CuInSe2 (up to 1.2 V between extreme modifications on Au and 0.3 V on CISe). The magnitude and direction of the observed contact potential difference changes were found to depend on the extent of coverage (as derived from electrochemical and contact angle measurements) and on the orientation of the ligands (estimated from ellipsometry and FTIR data) and could also be reconstructed using a simple, electrostatic model. These findings demonstrate that the present methodology enables simultaneous grafting of two desired properties onto solid surfaces and illustrate the predictive power of a simple, electrostatic model for molecule-controlled surface engineering.

A new kind of multilayers based on metal-ion coordination was constructed on gold surfaces, where molecular layers are successively added using a highly controlled step-by-step procedure. A bifunctional ligand is used as the base layer, bearing a cyclic disulfide group to attach to the gold surface and a bishydroxamate group capable of ion binding. An 8-coordinating metal ion such as Zr4+ or Ce4+ is then coordinated to the bishydroxamate site, followed by exposure to a second ligand possessing four hydroxamate groups. The tetrahydroxamate molecule ligates to the metal ion (bound to the base layer) using two of its four hydroxamate groups and is free to bind a second metal ion at its other end. A sequence of adsorption steps using metal ions and tetrahydroxamate ligands was carried out, resulting in an ordered metal−organic multilayer. Multilayer structures comprising up to 10 tetrahydroxamate/metal ion layers were constructed, with full characterization at each step of multilayer formation using ellipsometry, contact angle measurements, X-ray photoelectron spectroscopy, and Fourier transform infrared spectroscopy. The multilayer morphology and mechanical properties were studied by scanning force microscopy. It is shown that different base ligands induce dramatic differences in the morphology and stiffness of the final multilayer. The possibility to construct segmented multilayers containing Zr4+ and Ce4+ ions at defined locations is presented.

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A novel type of bilayer on a gold surface, based upon metal-ion coordination to hydroxamate moieties, is described. Tailor-made bifunctional ligands containing hydroxamate groups (for metal coordination) and a cyclic disulfide residue (for surface attachment) have been prepared. The bishydroxamate binding site forms 2:1 ligand/ metal complexes with octacoordinating metal ions such as Zr IV , Ce IV , and Ti IV ; the cyclic disulfide moiety anchors the complex to the gold surface. Two routes to bilayer formation are demonstrated: i) a one-step process from preformed 2:1 complexes, and ii) a stepwise process including formation of the ligand monolayers followed by binding of a guest ion and a second layer of ligand molecules.The former approach allows full characterization of the complexes before bilayer assembly, whereas the latter enables construction of either symmetric (identical) or asymmetric (nonidentical) bilayers. Both types of bilayers were characterized by ellipsometry, contact angle, and XPS measurements. Symmetric bilayers obtained by the two processes have similar properties.

We report the synthesis of a novel molecular switch based on a double-stranded ditopic ligand which operates through the Cu II /Cu I couple; the mononuclear cuprous and cupric complexes were characterised by absorption spectrophotometry; reversible motion of the copper ion between the two binding sites is driven by an auxiliary oxidation and reduction reaction; the rate-limiting steps of this translocation process were determined as well as the corresponding kinetic parameters.