Tuning the Mechanochemistry of the Au ? S interface

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

Viena

Congreso; STC 2014; 2014

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The interest in gold-based materials has dramatically increased over the last decade, due to their potential 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 that purpose. The understanding of the S ? Au interaction, thus, becomes highly relevant from a technological point of view. Most theoretical and computational studies only deal with the energetics of the S ? Au interface, but their mechanical properties have been much less explored.1 A recent computational study has shown that the strength of the S ? Au bond can be modulated by adequate substituents on the aromatic ring of thiophenol.2 We studied the mechanochemical behavior of a series of substituted-p-methyl-thiophenolates adsorbed on a flat Au(111), and 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 contrast, the aliphatic ethylthiolate, has 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. Electronic population analysis, differential charge density analysis and partitioning schemes such as EDA (Energy Decomposition Analysis) allow us to gain insight into the Au ? S interaction and rationalize the observed mechanochemical behavior. The effect of a defect in the surface, such as a vacancy, was also studied. 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. Finally, when ortho subtituents are present, the molecules detach with a very low rupture force, without modifying the underlying surface. This constitutes an additional way to tune the mechanical properties of the Au ? S interface. (1) Ribas-Arino, J.; Marx, D. Chem. Rev. 2012, 112, 5412?5487. (2) Miranda-Rojas, S.; Muñoz-Castro, A.; Arratia-Pérez, R.; Mendizábal, F. Phys. Chem. Chem. Phys. 2013, 15, 20363?20370.