Grafting of the gold surface by heterocyclic moieties derived through electrochemical oxidation of amino triazole – an experimental and “ab initio” study

Surface modification of gold is accomplished by using the aminyl radicals formed through the electrochemical oxidation of the amino-triazole molecule dissolved in organic media (acetonitrile). The electrochemistry of the grafting process and the redox behavior of the grafted heterocyclic layer are similar to those of aliphatic amines. The presence of AT groups on the electrode surface was studied by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) before and after the functionalization process to confirm and prove the formation of a layer on the surface. The capability of the modified surfaces for blocking redox reaction was assessed using a ferrocyanide–ferricyanide redox couple and displayed important differences. The redox probes display a decrease in electron transfer rate. The increase of the charge transfer resistance of the grafted layer is suggestive of a compact layer formation. Furthermore, the Au13 cluster was used to compute BDEs (bond dissociation energies) and a number of other important parameters such as bond strength and length of the interface, etc. These parameters were computed using ONTEP software (Order-N Total Energy Package), intended specifically for calculations on large systems, and it employs density functional theory (DFT) in the density matrix formulation.

Surface modification of gold is accomplished by using the aminyl radicals formed through the electrochemical oxidation of the amino-triazole molecule dissolved in organic media (acetonitrile).

Experimental and Theoretical Study of the Covalent Grafting of Triazole Layer onto the Gold Surface

Finding novel strategies for surface modification is of great interest in electrochemistry and material sciences. In this study, we present a strategy for modification of a gold electrode through covalent attachment of triazole (TA) groups. Triazole groups were electrochemically grafted at the surface of the electrode by a reduction of in situ generated triazolediazonium cations. The resulting grafted surface was characterized before and after the functionalization process by different electrochemical methods (cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS)) confirming the presence of the grafted layer. The grafting of TA on the electrode surface was confirmed using analysis of surface morphology (by atomic force microscopy), the thickness of the grafted layer (by ellipsometry) and its composition (by X-ray photoelectron spectroscopy). Density functional theory (DFT) calculations imply that the grafted triazole offers a stronger platform than the grafted aryl layers.

Spectroscopic Identification of the Au-C Bond Formation upon Electroreduction of an Aryl Diazonium Salt on Gold

Electroreduction of aryl diazonium salts on gold can produce organic films that are more robust than their analogous self-assembled monolayers formed from chemical adsorption of organic thiols on gold. However, whether the enhanced stability is due to the Au-C bond formation remains debated. In this work, we report the electroreduction of an aryl diazonium salt of 4,4'-disulfanediyldibenzenediazonium on gold forming a multilayer of Au-(Ar-S-S-Ar)_n, which can be further degraded to a monolayer of Au-Ar-S^- by electrochemical cleavage of the S-S moieties within the multilayer. By conducting an in situ surface-enhanced Raman spectroscopic study of both the multilayer formation/degradation and the monolayer reduction/oxidation processes, coupled to density functional theory calculations, we provide compelling evidence that an Au-C bond does form upon electroreduction of aryl diazonium salts on gold and that the enhanced stability of the electrografted organic films is due to the Au-C bond being intrinsically stronger than the Au-S bond for a given phenylthiolate compound by ca. 0.4 eV.

Functionalization of nanomaterials with aryldiazonium salts

This paper reviews the surface modification strategies of a wide range of nanomaterials using aryldiazonium salts. After a brief history of diazonium salts since their discovery by Peter Griess in 1858, we will tackle the surface chemistry using these compounds since the first trials in the 1950s. We will then focus on the modern surface chemistry of aryldiazonium salts for the modification of materials, particularly metallic, semiconductors, metal oxide nanoparticles, carbon-based nanostructures, diamond and clays. The successful modification of sp(2) carbon materials and metals by aryldiazonium salts paved the way to innovative strategies for the attachment of aryl layers to metal oxide nanoparticles and nanodiamonds, and intercalation of clays. Interestingly, diazotized surfaces can easily trap nanoparticles and nanotubes while diazotized nanoparticles can be (electro)chemically reduced on electrode/materials surfaces as molecular compounds. Both strategies provided organized 2D surface assembled nanoparticles. In this review, aryldiazonium salts are highlighted as efficient coupling agents for many types of molecular, macromolecular and nanoparticulate species, therefore ensuring stability to colloids on the one hand, and the construction of composite materials and hybrid systems with robust and durable interfaces/interphases, on the other hand. The last section is dedicated to a selection of patents and industrial products based on aryldiazonium-modified nanomaterials. After nearly 160 years of organic chemistry, diazonium salts have entered a new, long and thriving era for the benefit of materials, colloids, and surface scientists. This tempts us to introduce the terminology of "diazonics" we define as the science and technology of aryldiazonium salt-derived materials.