Figure 1 :  sexithiophene                                      Figure 2: Schematic representation of the device
Molecular electronics follows a “bottom-up” approach to electronics materials—understanding the fundamental limit of a molecular wire or molecular transistor. Unlike conventional silicon-based computer chips, which have become smaller through “top-down” improvements in the ability to define features using lithography and etching processes, molecular electronics seeks to characterize the conductance and electronic structure of single molecules and molecular ensembles. These techniques can address fundamental questions of the chemistry and physics of molecules on the nanoscale and we use an interdisciplinary approach using the tools of synthetic chemistry to design deliberate molecular architectures, nanofabrication, careful and reproducible electrical measurements, electrochemistry, and theoretical modeling of such devices.

In the Abruña group, we focus on two different classes of potential molecular wires: organic conducting polymers and transition-metal coordination complexes. Both types of molecules are synthesized in the group, studied by standard analytical and electrochemical means in solution, bulk, and thin-films, and then used to fabricate nanoscale electrical devices. Both classes of molecules are highly stable and allow synthetic tailorability to study changes in the electronic properties.

Organic conducting polymers have been widely studied for applications in printed electronics, thin-film transistors, solar cells, and light-emitting diodes. Polymers and well-defined oligomers of polythiophene, polyanaline, and other polymers are used as potential molecular wires.

        

    Figure 3 :  [Ru5[tppz]6]10+                                                                      Figure 4: SEM image of the device

For transition-metal complexes, we focus on tridentate, linear bridging ligands such as TPPZ, which can be used to create polymeric and well-defined multimetallic oligomers. The high degree of electronic communication between metal centers should be ideal for highly conductive molecular wires.

We created a series of molecules that can be switched from conducting to non-conducting with a flash of light. Importantly, the molecule stays the same length during this switching action which will allow us to suspend this molecule between two tiny gold wires to create the world’s smallest switch. These switches will help us understand how and why molecules conduct electricity at the atomic scale.

        switch             

 Figure 5: Schematic of the solution phase device            Figure 6: Molecular switch on a break junction device