Synthesis of an Anthraquinone-Bridged bis(terpyridine) Ligand and its Use in the Stepwise Fabrication of Complex Oligomer Wires on Gold

One-step vs stepwise immobilization of 1-D coordination-based Rh-Rh molecular wires on gold surfaces

Reaction of dimeric [Rh(II)(2)(phen)(2)(μ-OAc)(2)(MeCN)(2)](BF(4))(2) (phen =1,10-phenanthroline) with pyrazine (pz) in a 1:2 ratio leads to the new 1-D metal-metal-bonded coordination oligomer {[Rh(II)(2)(phen)(2)(μ-OAc)(2)(pz)](BF(4))(2)}(n) (Rh-Rhpz)(n) (1), where each Rh atom of the dimeric unit (Rh-Rh) is coordinated in the equatorial plane to a nitrogen atom of a rigid and linear bifunctionalized organic linker (pz). Single X-ray diffraction analysis reveals the 1-D straight oligomeric chain structure (molecular wire, MW) consists of alternating (Rh-Rh) units and pz linking ligands with free BF(4)(-) as counteranions, and each metal center has a slightly distorted octahedral arrangement. The presence of accessible labile MeCN groups on both ends of these MWs ("free ends") enables functionalization of a 4-mercaptopyridine-gold coordinating platform (Au/MP) to form in one step a layer of coordination oligomer (Au/MP(Rh-Rhpz)(n); n ≈ 50). Furthermore (Rh-Rhpz)(n) (n = 1-6) MWs were grafted to Au/MP surfaces by a conventional step-by-step assembly construction involving coordination reactions between the Rh dimer ([Rh(2)(phen)(2)(μ-OAc)(2)(MeCN)(2)](BF(4))(2) (2)) and pz. A detailed physicochemical study (UV-vis, RAIR, QCM-D, ellipsometry, contact angle measurements, as well as impedance spectroscopy and cyclic voltammetry) has been made during both assembly methods to characterize the resulting surface-anchored coordination molecular wire (CMW) layers (Au/MP(Rh-Rhpz)(n)). The results indicate that the immobilized molecular assemblies (MAs) were successfully fabricated using both methods of assembly. The efficiency of the two methods is discussed.

Terpyridine-functionalized surfaces: redox-active, switchable, and electroactive nanoarchitecturesgland

Terpyridines represent versatile functional supramolecular building blocks that are easily integrated in numerous devices and can readily modify surfaces. In particular, redox-active complexes with terpyridine ligands have been attached to surfaces, either by covalent or non-covalent interactions, and form highly ordered mono- or multilayer systems, since electronic and charge transport properties are major topics of interest. Their applications in nanoelectronics are a driving force for understanding and enabling the utilization of the supramolecular properties of terpyridines for surface modification. This area of research has received increasing attention during the last decade leading into the supramacromolecular regime. This Progress Report presents an overview of the state-of-the-art of surface modifications utilizing terpyridine systems and highlights main results, as well as modern trends, in this research area.

Surface junction effects on the electron conduction of molecular wires

Surface junction effects on the electron conduction of p-phenylene-bridged bis(terpyridine)iron oligomers terminated with a ferrocene moiety were quantitatively analyzed by employing three different surface-anchoring terpyridine ligands. The dependence of the electron-transfer rate constant for oxidation of the ferrocene moiety, k(et), on the distance between the electrode surface and the ferrocene moiety, x, showed that the attenuation factor, beta(d), which indicates the degree of reduction of k(et) with x, was approximately 0.018 in all cases. However, the absolute k(et) value depended strongly on both electronic and steric factors of the surface-anchoring ligand.

Superior electron-transport ability of pi-conjugated redox molecular wires prepared by the stepwise coordination method on a surface

Electronic conductivity of molecular wires is a critical fundamental issue in molecular electronics. pi-Conjugated redox molecular wires with the superior long-range electron-transport ability could be constructed on a gold surface through the stepwise ligand-metal coordination method. The beta(d) value, indicating the degree of decrease in the electron-transfer rate constant with distance along the molecular wire between the electrode and the redox active species at the terminal of the wire, were 0.008-0.07 A(-1) and 0.002-0.004 A(-1) for molecular wires of bis(terpyridine)iron and bis(terpyridine)cobalt complex oligomers, respectively. The influences on beta(d) by the chemical structure of molecular wires and the terminal redox units, temperature, electric field, and electrolyte concentration were clarified. The results indicate that facile sequential electron hopping between neighboring metal-complex units within the wire is responsible for the high electron-transport ability.