Electron transfer through organic molecules

Electron transfer through molecular frameworks is central to a wide range o f chemical, physical, and biological processes. We demonstrate a means to m easure electronically and to quantify electron transfer through organic mol ecules and films. We show quantitative agreement with universal values of e lectron transfer inferred from biological, electrochemical, photochemical, and related systems. Scanning tunneling microscopy was used to image adjace nt chains and molecular terraces of different length alkanethiolates in an ordered self-assembled monolayer lattice on Au{111}. In electron transfer m easurements using a scanning tunneling microscope, both the driving force a nd the electrode separation can be continuously varied. This allows indepen dent electronic measurement of the molecular bridges through which electron transfer takes place. The differences between the measured topography in s canning tunneling microscopy and the physical heights of these molecules ca n be understood in terms of the transconductance through individual chains using a two-layer tunnel junction model.