Conductance switching in a molecular device: The role of side groups and intermolecular interactions

We report first-principles studies of electronic transport in monolayers of Tour wires functionalized with different side groups. An analysis of the scattering states and transmission eigenchannels suggests that the functionalization does not strongly affect the resonances responsible for current flow through the monolayer. However, functionalization has a significant effect on the interactions within the monolayer, so that monolayers with ${\mathrm{NO}}_2$ side groups exhibit local minima associated with twisted conformations of the molecules. We use our results to interpret observations of negative differential resistance and molecular memory in monolayers of ${\mathrm{NO}}_2$ functionalized molecules in terms of a twisting of the central ring induced by an applied bias potential.