I/V characteristics of a molecular switch

We present a study of the conduction properties of a class of aromatic compounds, whose conformation can be modulated with a transverse electric field, with strong effects on the molecular transport properties. The theoretical method includes the molecule-electrode interaction in a simple, although effective way: the coupling matrix elements are considered independent from the energy of the continuum spectrum of the lead. This results in a simple expression for the molecular Green's function with a significant simplification in the expression of the transmission function. The effects of the voltage bias on the electronic molecular density is included through a uniform effective electric field. A simplified but accurate method for the evaluation of the molecular response to the field, which spares lengthy computations for each value of the voltage, is presented. The proposed method is calibrated on the widely studied benzene-1,4-dithiol molecule. The calculations on the selected molecular wire (a tetracyano derivative of 4,4'-di(mercaptoethynyl)tolan) show that conductivity is low for perpendicular rings, whereas conduction is allowed for the planar conformation, which corresponds to the equilibrium geometry in the absence of the transverse electric field.