Calculation of negative differential resistance in transport through benzene ring chains with NO2 side-group

We describe a model, incorporating photon-assisted tunneling, certain localized states and bond-bending, to account for the observed transport characteristics between gold leads through a triple benzene molecule with NO2 side-group (2′-amino-4-ethynylphenyl-5′-nitro-1-benzenethiolate). The model provides a natural explanation for the characteristic large negative differential resistance which emerges only when the NO2 side-group is present.