Electrochemical Control of Electron Transport in single Redox Molecules.

Studying electron transport in single molecules is not only a basic step towards single molecule electronic devices, but also critical for a better understanding of many chemical and biological processes. With prior NSF support, we have developed an experimental approach that can connect a single molecule to two electrodes and measure electron transport through the molecule in an electrochemical cell.[1-3] We have also shown that the transport current can be switched on and off by controlling the redox state of the molecule.[4-6] Building upon these advances, we wish to address several basic questions in electron transport via single redox molecules: What is the most efficient electron transport in single redox molecules? What are the barriers that prevent us from achieving the highest transport efficiency? How can we overcome these barriers? Polycyclic aromatic hydrocarbons are a good model system for us to address these questions. The simplest one is benzene[7,8] which is considered to be insulating or poorly conductive, due to its large LUMO-HOMO gap. The other side of the spectrum is graphene, consisting of infinite number of aromatic rings, which has a zero energy gap between the conduction (~LUMO) and valence (~HOMO) bands. Recent experimental and theoretical works have shown great promise of graphene for many important applications ranging from high performance field-effect electronic devices to novel chemical and biological sensors.[9,10] Studying the system provides us with a unique opportunity to understand electron transport in redox molecules and to bridge the gap between electron transfer phenomena in small redox molecules and electron transport properties in nanostructures, such as graphene.