Selective Nsp2- and Csp2- photografting of Au-Surface by aryldiazonium salts and arylazo sulfonates.

Arylazo sulfonates (Ar-N=N-SO3Na) were found to undergo photografting on gold surface through both Au-Nsp2- and Au-Csp2- bond formation. The functionalized materials have been fully characterized by Infrared reflection absorption spectroscopy (IRRAS), Raman, XPS, DFT calculations and UV-Vis absorption spectroscopy. These methods permit to evidence aromatic substituents (IRRAS), the Au-N=N signature (Raman and XPS spectroscopy) and the Bond Dissociation Energy values of the two linkages (DFT calculation). The grafting proceeds through two competitive paths, namely a stepwise reaction involving an aryl radical (for the formation of the Au-Ar bonds) and a concerted reaction on the surface of gold (for Au-N=N-Ar bond formation). The occurrence of an aryl radical upon irradiation has been fully evidenced via EPR spectroscopy. Finally, E/Z photoisomerisation of the N=N bonds present on prepared few layers films was observed by means of UV-Vis absorption spectroscopy.