Adsorption of 1,3-benzenedithiol and 1,3-benzenedimethanethiol on gold surfaces.

The adsorption characteristics of 1,3-benzenedithiol (1,3-BDT) and 1,3-benzenedimethanethiol (1,3-BDMT) on Au surfaces are investigated by means of surface-enhanced Raman scattering, UV/Vis absorption spectroscopy, and cyclic voltammetry (CV). 1,3-BDMT is found to adsorb via two S-Au linkages at concentrations below monolayer coverage, but to have an upright geometry as the concentration increases on Au nanoparticles. On the other hand, 1,3-BDT is found to adsorb by forming two S-Au linkages, regardless of concentration, based on the disappearance of the nu(SH)(free) stretching band. Because of the absence of the methylene unit, 1,3-BDT appears not to self-assemble efficiently on Au surfaces. The UV/Vis absorption spectroscopy and CV techniques are also applied to check the formation of self-assembled monolayers of 1,3-BDT and 1,3-BDMT on Au. Density functional theory calculations based on a simple adsorption model using an Au(8) cluster are performed to better understand the nature of the adsorption characteristics of 1,3-BDT and 1,3-BDMT on Au surfaces.