Coordination-Controlled Self-Assembled Multilayers on Gold

Abstract

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.

Sensitivity of Transmission Surface Plasmon Resonance (T‐SPR) Spectroscopy: Self‐Assembled Multilayers on Evaporated Gold Island Films

“…Au) with the number of organic layers indicates regular growth of the film thickness, as shown for coordination multilayers grown on a continuous, 100-nm-thick gold substrate. [43][44][45] It is therefore concluded that the construction of coordination multilayers on the Au island films proceeds in a regular fashion, such that the contribution of each additional organic layer to the overall film thickness is approximately the same. The thickness increment per added monolayer is assumed to be approximately 1.4 nm, as measured on continuous gold substrates (see above).…”

“…Details on the Au island film properties are given elsewhere. [33] Construction of coordination-based self-assembled multilayers on the Au island films generally followed our previously published methodology, [42][43][44] shown schematically in Figure 1. The anchor monolayer adsorbed directly on the Au islands comprised the disulfide-bishydroxamate molecule 1, while the repeat unit was the bifunctional tetrahydroxamate ligand 2, coordinated through Zr IV ions.…”

Surface‐Grafted Multiporphyrin Arrays as Light‐Harvesting Antennae to Amplify Photocurrent Generation

“…The SAM was also characterized by using [Fe(CN) 6 ] 3À as a bulk redox probe. [16] The electrode surface covered with the SAM was completely insulated from the bulk ferricyanide species, even after the zinc insertion (Figure 3b).…”

“…Metal-ligand interaction is a powerful tool to build structurally regular multilayered assemblies on conductive surfaces. [6] Besides, the fully conjugated metal complexes may enhance electronic and optical communications among the individual layer constituents. The porphyrin macrocycle is the fundamental chromophore framework in natural photosynthetic systems, in which the special pair collects solar energy from the peripheral light-harvesting antennae with excellent yields.…”

Design and self-assembly of wide and robust coordination cages

“…8). Specifically, surface-controlled self-assembly is rapidly emerging as a valuable tool for the generation of complex structures directly on solid supports (9)(10)(11). Unlike the covalent approach used for carcerands synthesis (12), the thermodynamic control of the process conveys interesting features, among which reversibility (13), selection (14), and self-repairing properties are the most interesting.…”