Arylazo sulfonates (ArÀ N=NÀ SO 3 Na) have been found to undergo photografting on gold surface through both AuÀ N sp2 À and AuÀ C sp2 À 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 AuÀ 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 AuÀ Ar bonds) and a concerted reaction on the surface of gold (for AuÀ N=NÀ Ar bond formation). The occurrence of an aryl radical upon irradiation has been fully evidenced by EPR spectroscopy. Finally, E/Z photoisomerisation of the N=N bonds present on prepared few layer films has been observed by means of UV-Vis absorption spectroscopy.
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