  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 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 NO$_2$
functionalized molecules in terms of a twisting of the central ring induced by
an applied bias potential.
