Single molecule conductance of linear dithioalkanes in the liquid phase: Apparently activated transport-due to conformational flexibility

We computed the single molecule conductance of a series of linear alpha-omega-dithiolalkanes as a function of their conformation, following experimental evidence (Haiss et al. Faraday Discuss. 2006, 131, 253) that even these simple molecules exhibit a thermal gating of electron transfer. After performing a conformational search using the MM3 empirical force-field, for each conformation, we evaluated the conductance using DFT single point calculations and Green's function theoretical approach. We analyzed the complex dependence of the conductance on the conformation, discussing its correlation with the conformational energy and the molecule end-to-end distance. From this data, the temperature dependence of conductance was calculated. Our calculations confirm that the conformational flexibility of the alkylic chain led to a higher conductance at higher temperatures. Therefore, the electron transport in these junctions appears to be thermally activated even if it takes place by pure tunneling.