Mixed Azide-Terminated Monolayers:  A Platform for Modifying Electrode Surfaces

Abstract

We have prepared and characterized mixed self-assembled monolayers (SAM) on gold electrodes from azido alkane thiols and various omega-functionalized alkane thiols. In the presence of copper(I) catalysts, these azide-modified surfaces are shown to react rapidly and quantitatively with terminal acetylenes forming 1,2,3-triazoles, via "click" chemistry. The initial azide substituents can be identified and monitored using both grazing-angle infrared (IR) and X-ray photoelectron spectrosopies. Acetylenes possessing redox-active ferrocene substituents react with the azide-terminated mixed SAMs and electrochemical measurements of the ferrocene-modified SAM electrodes have been used to quantify the redox centers attached to these platforms. Time-resolved electrochemical measurements have enabled us to follow the formation of these ferrocene centers and thus to measure the rate of the surface "click" reaction. Under optimal conditions this well-behaved second-order reaction takes place with a rate constant of 1 x 10(3) M(-)(1) s(-)(1). Typical reaction times of several minutes were realized using micromolar concentrations of acetylene. These techniques have been used to construct well-characterized, covalently modified monolayers that can be employed as functional electrode surfaces.

Azidation of Silicon(111) Surfaces

“…15 Partial methoxylation of the surface 17 may also contribute to this. The inset of Figure 1A shows two peaks at 400 and 404 eV with an intensity ratio of 2:1, similar to what is seen for azide groups on gold 18 and graphitic 19 surfaces. No sodium signal was observed from the azide-modified surfaces.…”

O 2 reduction by a functional heme/nonheme bis-iron NOR model complex

“…The Au electrode was also electrochemically cleaned before experiments by several CV cycles between 1,650 and Ϫ200 mV at 250 mV in 0.5 H 2SO4. The azide-terminated thiols were synthesized and characterized as reported previously (33,45). The mixed thiol monolayer was deposited by immersing the cleaned IDAs in a 0.4 mM solution of a mixture of azide-terminated thiol and thiols in ethanol for 1 h.…”

The molecular level modification of surfaces: from self-assembled monolayers to complex molecular assemblies

“…The excitement generated by this class of chemistry for surface modification may be traced back to a report from Chidsey and co-workers in which was claimed quantitative (for coverages lower than the steric limit) coupling between a surface azide and a solution alkyne species. 149,150 Remarkably, when an alkyne-tagged ferrocene derivative was ''clicked'' onto an azide-modified gold electrode, cyclic voltammograms with DE fwhm values close to 90.6/n were observed. That is, as referred to in case study 1 (Section 3.1), this chemistry allowed the stepwise fabrication of a redox interface with nearly ideal electrochemical behaviour.…”