10.1021/nn505115a.s001 Fatemeh Mirjani Fatemeh Mirjani Joseph M. Thijssen Joseph M. Thijssen George M. Whitesides George M. Whitesides Mark A. Ratner Mark A. Ratner Charge Transport Across Insulating Self-Assembled Monolayers: Non-equilibrium Approaches and Modeling To Relate Current and Molecular Structure American Chemical Society 2014 carbon chains charge transport charge Transport Molecular StructureThis paper SAM tail groups increases HS tail groups R entity molecule thiol group tail group R R group quantum methods 2014-12-23 00:00:00 Journal contribution https://acs.figshare.com/articles/journal_contribution/Charge_Transport_Across_Insulating_Self_Assembled_Monolayers_Non_equilibrium_Approaches_and_Modeling_To_Relate_Current_and_Molecular_Structure/2223130 This paper examines charge transport by tunneling across a series of electrically insulating molecules with the structure HS(CH<sub>2</sub>)<sub>4</sub>CONH(CH<sub>2</sub>)<sub>2</sub>R) in the form of self-assembled monolayers (SAMs), supported on silver. The molecules examined were studied experimentally by Yoon <i>et al</i>. (<i>Angew. Chem. Int. Ed</i>. <b>2012</b>, <i>51</i>, 4658–4661), using junctions of the structure AgS(CH<sub>2</sub>)<sub>4</sub>CONH(CH<sub>2</sub>)<sub>2</sub>R//Ga<sub>2</sub>O<sub>3</sub>/EGaIn. The tail group R had approximately the same length for all molecules, but a range of different structures. Changing the R entity over the range of different structures (aliphatic to aromatic) does not influence the conductance significantly. To rationalize this surprising result, we investigate transport through these SAMs theoretically, using both full quantum methods and a generic, independent-electron tight-binding toy model. We find that the highest occupied molecular orbital, which is largely responsible for the transport in these molecules, is always strongly localized on the thiol group. The relative insensitivity of the current density to the structure of the R group is due to a combination of the couplings between the carbon chains and the transmission inside the tail. Changing from saturated to conjugated tail groups increases the latter but decreases the former. This work indicates that significant control over SAMs largely composed of nominally insulating groups may be possible when tail groups are used that are significantly larger than those used in the experiments of Yoon <i>et al</i>.