Mechanochemical Properties of Aliphatic and Aromatic Thiolates Adsorbed on Gold

MARTIN E. ZOLOFF MICHOFF; JORDI RIBAS-ARINO; DOMINIK MARX

Coventry

Workshop; Computational Molecular Science 2015; 2015

University of Warwick

The interest in gold-based materials has dramatically increased over the last decade, due to theirpotential applications in diverse fields, such as molecular biology, catalysis and molecular electronic devices. Much of these applications involve the modification of the metallic surface by incorporating molecules that provide new properties to the material. Due to the strength of the S-Au bond, thiols have been widely used for this purpose. The understanding of the S-Au interaction, thus, becomes highly relevant from a technological point of view. Most theoretical and computational studies performed so far have only dealt with the energetics of the S-Au interface, but their mechanical properties have been much less explored.Inspired by a recent computational study in which it was shown that the strength of the S-Au bond can be modulated by substituting adequate positions on the aromatic ring of thiophenol,we carried out a systematical study of the mechanochemical behavior of a series of substituted-p-methyl-thiophenolates adsorbed on a flat Au(111). We found that although the binding energy can be modified up to ~30%, all the species display a similar mechanical detachment scenario, in which the radical thiophenolate is detached from the surface. In stark contrast, the aliphatic ethylthiolate displays a binding energy very similar to that of the strongest binding thiophenolate, but it is mechanically detached from the surface through a completely different pathway, that involves the detachment of gold atoms. These results can be understood in terms of different electronic structure analysis.The effect of a defect in the surface, such as a vacancy, was also explored. For the aliphatic thiolate,the mechanical behavior displayed is similar to that on the flat perfect Au(111) surface. On the other hand, the mechanical detachment pathway of the thiophenolate on the defective surface resembles that of the aliphatic thiol on both types of surface, ie. involving the detachment of gold atoms.Interestingly, although the binding on the defective surface is higher than that on the perfect Au(111)surface, the mechanical stability of the Au-S interface decreases, since it detaches with a lower rupture force. This is due to the fact that Au-Au bond breakage occurs.