Metal ion reactivity with 1,4-benzenedimethanethiol monolayers on gold

Exposure of Cu2+ ions to 1,4-benzenedimethanethiol (BDMT) monolayers on Au in solution results in the formation of copper functionalized monolayers wh ich have been investigated in detail by surface-enhanced Raman spectroscopy (SERS), X-ray photoelectron spectroscopy (XPS), and cyclic voltammetry (CV ). Upon exposure to copper ions, the free thiol groups at the surface of th e monolayer disappear indicating the replacement of protons with copper ion s. The reaction leads to a red shift in the C-S stretching frequency, but m ost of the other features are unaffected. Relative intensities of the peaks are largely the same; however, some new features are observed suggesting m inor changes in the adsorbate structure that makes additional modes observa ble. Thermal stability of the monolayers has been reduced substantially as a result of reaction with metal ions, indicating that the chemical binding at the Au-monolayer interface is affected. XPS shows that copper is present at the surface. Electrochemical behavior before and after Cu2+ ion adsorpt ion is significantly different, and the adsorbed metal ions undergo reversi ble redox transformations. The cyclic voltammograms of the adsorbed copper ions are discussed in relation to the oxidation state changes in aqueous el ectrolyte solutions.