Extracting Quantitative Information of electronic structures from Tunneling Molecular Junction I-V Characteristics using a Compact Analytical Model

One of the central challenges of molecular electronics is to establish clear connections between molecular structure, the ensuing electronic structure, and the current-voltage (I-V) characteristics of molecular junctions. In particular, the offset ε_h of the Fermi level relative to the appropriate frontier molecular orbital (HOMO in this case) and the electrode-molecule coupling strength Γ are recognized as two main factors that determine the electrical properties of a typical molecular junction. We show that a compact analytical model derived from the Landauer formalism provides a quantitative fit to the I-V data and yields values of ε_h and Γ that vary systematically with molecular structure and choice of electrode materials. We will present transport data and theoretical analysis of tunnel junctions based on oligophenylene monothiols and dithiols – with systematically varying lengths – and electrodes fabricated from Ag, Au and Pt metals. Furthermore, Ultraviolet photoelectron spectroscopy (UPS) was employed to determine the ε_h to be compared with the values predicted by the model from transport data. We will emphasize that the compact analytical analysis facilitates structure-property correlations and a powerful physical organic chemistry approach to molecular electronics.