The objective of this project is to gain control on the mechanism of transport properties of Self Assembled Monolayer (SAM)-based molecular tunnel junctions. The methodology developed by the Whitesides group over the last few years has allowed to increase the reliability of molecular tunnel junctions, allowing to measure their tunnel transport rates with much more accuracy than it had been possible until now, demonstrating how SAMs of alkylthiolates on Ag with odd or even number of atoms show different conductivities. The Whitesides group has also demonstrated the efficient rectification of Fc-terminated SAMs and suggested a mechanism to explain this result. In this project, we propose to rationally engineer the orbital energies of SAMs terminal groups in order to obtain predictable tunneling and/or hopping behaviors. The good development of this project will require the fellow to identify the target molecules by Ab Initio calculations, to engage in organic synthesis to prepare them, and to use a wide range of material science techniques to prepare, characterize and analyze the transport properties of their SAMs. The knowledge acquired by the fellow in Prof. Whitesides group in Harvard will then be transferred to the use of tunnel junctions bearing molecular magnetic end-groups, including SIngle Molecule Magnets, and potentially allowing to design and prepare highly magnetoresistive junctions. The outcome of this work would on one hand improve the fundamental knowledge on molecular tunnel junctions, potentially allowing to use them for molecular electronics, and could provide highly functional molecular spintronics devices by fine tuning of their spin injection barriers.