Silicon (100) Electrodes Resistant to Oxidation in Aqueous Solutions: An Unexpected Benefit of Surface Acetylene Moieties

Abstract

Here we report on the functionalization of alkyne-terminated alkyl monolayers on highly doped Si(100) using "click" reactions to immobilize ferrocene derivatives. The reaction of hydrogen-terminated silicon surfaces with a diyne species was shown to afford very robust functional surfaces where the oxidation of the underlying substrate was negligible. Detailed characterization using X-ray photoelectron spectroscopy, X-ray reflectometry, and cyclic voltammetry demonstrated that the surface acetylenes had reacted in moderate yield to give surfaces exposing ferrocene moieties. Upon extensive exposure of the redox-active architecture to oxidative environments during preparative and characterization steps, no evidence of SiOx contaminants was shown for derivatized SAMs prepared from single-component 1,8-nonadiyne, fully acetylenylated, monolayers. An analysis of the redox behavior of the prepared Si(100) electrodes based on relevant parameters such as peak splitting and position and shape of the reduction/oxidation waves depicted a well-behaved redox architecture whose spectroscopic and electrochemical properties were not significantly altered even after prolonged cycling in aqueous media between -100 and 800 mV versus Ag|AgCl. The reported strategy represents an experimentally simple approach for the preparation of silicon-based electrodes where, in addition to close-to-ideal redox behavior, remarkable electrode stability can be achieved. Both the presence of a distal alkyne moiety and temperatures of formation above 100 degrees C were required to achieve this surface stabilization.

10 Years of Click Chemistry: Synthesis and Applications of Ferrocene‐Derived Triazoles

“…Longer linkers act as dielectrics and hamper the electron flow. [66][67][68] Dubacheva and co-workers recently demonstrated the binding of ferrocene polymers into the hydrophobic pocket of CD. The CDs were introduced by using click chemistry on preformed SAMs on gold surface; they showed the association and dissociation of ferrocene polymers into CD during the redox process.…”

“…The application of voltage across the functionalized electrode resulted in uncapping due to the oxidation of ferrocene to ferrocenium species. [67] Nanomaterials and Supramolecular Assemblies Nanotubes, nanofibers, and other nanoscale materials show unusual properties in catalysis, electrical conductivity, the design of lightweight materials, and so on relative to the bulk matter. Functionalization of the surface of these nanomaterials with specially designed molecules promises the generation of materials with extraordinary functions.…”

Click Chemistry‐Based Functionalization on Non‐Oxidized Silicon Substrates

“…[79,80] Indeed, reducing the surface density of the alkyne moieties is helpful to improve "click" coupling efficiencies, as demonstrated for organic monolayers composed of a mixture of 1,8-nonadiyne/1-heptyne. [61] With progressive dilutions of the diyne mole fraction from 1.00 to 0.05, close to quantitative yield was achieved according to the electrochemical characterization. However, this approach does not actually improve the surface density of the immobilized molecules.…”

“…Both the presence of a distal alkyne moiety and temperatures of formation above 100 8C were critical to achieve this surface stabilization. [61] By taking advantage of the same platform developed by Gooding s group, Liu et al have also demonstrated the first example of attaching b-azidometalloporphyrins on a SiA C H T U N G T R E N N U N G (100) substrate. [62] The high-quality modified silicon electrodes with well-defined electrochemistry open the door to using such surfaces in biosensing and memory devices.…”

“…In contrast, some small and unhindered amines, such as ligand TMEDA (Scheme 7) used by Gooding et al, seems quite effective to increase the reaction rate and improve the coupling yield. [57,61] On our TMG-alkyne-terminated surface, we also tested several ligands with triazole moieties, [77,85,86] and identified the most efficient ligand TA-EG4 (Scheme 8). The OEG chain renders the Cu I complex water soluble, and the electron-donating NHCH 3 group maintains a high catalytic activity of the complex.…”