The interaction of alkanethiolates with small coinage metal clusters of copper and gold was studied based on density functional theory with a focus on the metal-thiolate junction. Calculation of fragmentation energies indicate that for Cu(n)-thiolate (n = 1,3,5,7, and 9) there is a progressive lowering in energy for the fragmentation of the S-C bond in the thiolate from a value of 2.9 eV for n = 1 to 1.4 eV for n = 9. The detailed electronic origins of this specific weakening are attributed to a polarization of electron density in the S-C bond as induced by bonding with the Cu(n) cluster. For the gold analogues, this effect is not observed and fragmentation at the S-C bond experiences only a slight 10% destabilization as n increases from 3 to 9. The relativistic origin of this difference between Cu and Au is discussed, and an analysis of bonding considerations is presented.

Optical, purely mechanical, and combined opto-mechanical switching cycles of a molecular switch embedded in a metal junction are investigated using density functional theory and (excited state) ab initio molecular dynamics. The nanomechanical simulations are done on realistic models of gold electrode tips bridged by a single dithioazobenzene molecule. Comparison of different tip models shows that the nature of the tips affects switching processes both qualitatively and quantitatively. The study predicts that purely photochemical cis⇌trans switching cycles of suspended azobenzene bridges are mechanically hindered; combined opto-mechanical as well as purely mechanochemical forward and backward switching is, however, feasible.

Most chemical reactions require activation which is conventionally supplied by heat. In stark contrast, mechanical activation by applied external forces opens intriguing novel possibilities. Here, the first direct comparison of mechanical versus thermal activation of bond breaking is provided. Studying both thiolate-copper interfaces and junctions provides evidence for vastly different reaction pathways and product classes. This is understood in terms of directional mechanical manipulation of coordination numbers and system fluctuations in the process of mechanical activation.

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