Structural and electronic properties of thiophenethiolate chemisorbed and thiophene physisorbed on Au(111) layer have been studied by model rooted in the density functional theory. In particular, the changes in workfunction and ionization potential upon chemisorption or physisorption have been evaluated by chemical anchoring the thiol S atom above different sites and rationalized in terms of the surface dipole of the self assembled monolayer and charge reorganization. The most stable adsorption site is in the bridge configuration and the general rule stating that large variation of the tilt angle gives small shift in work function with respect to the clean Au(111) surface is confirmed. However, the work function shift is strongly dependent on the site of chemical bonding, either bridge or top site. The co-facial interaction in the thiophenethiolate systems that comes into play when the molecule is very tilted on the surface has also been investigated within a conformational study. Afterward, the bond interaction between the sulfur atom of the ring and the gold surface gives rise to a fast decrease of the workfunction. © Springer-Verlag 2009.

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