By high school, I knew that I wanted to be a chemist. I spent many hours with a Gilbert chemistry set; I took fireworks apart and developed my own pyrotechnic mixtures; I inflated balloons with hydrogen from aluminum foil and caustic soda. Consequently, I matriculated as a chemistry major in college and never deviated from that path.

The use of self-assembled monolayers (SAMs) on electrodes has greatly enhanced two areas of research. The blocking abilities of SAMs are potentially useful for studying long range electron transfer for solution redox molecules and for the development of selective electrodes. We developed methods for mapping the pinholes and defects in the SAMs and for passivating the pinholes. The attachment of redox molecules to the external surface of a SAM on an electrode has been a powerful tool for probing the factors that affect the rate of electron transfer between the electrode and the molecule. We and others have shown that the rate of electron transfer displays a distance dependence consistent with tunneling and a potential dependence consistent with Marcus theory. The potential dependence allows extraction of the reorganization energy of the redox molecule, an important parameter in Marcus theory. More recently, we demonstrated that the rate of electron transfer is nearly independent of the metal used as the electrode.

One of the greatest challenges was finding conditions for preparing a perfectly blocking SAM for freely diffusing redox couples. We never achieved that goal. Only one other researcher consistently produced SAMs that displayed electron tunneling in the absence of currents due to pinholes and defects.

The serendipitous event was the choice of a ruthenium pentaammine pyridine redox center for our initial work. This redox center was easy to make and easy to attach to SAMs. It proved to be well-behaved; close to theoretical responses were obtained in voltammetry experiments. Most of our fundamental work on factors affecting the kinetics of electron transfer used this redox center.

Fundamental understanding of the factors affecting heterogeneous electron transfer kinetics has been hampered by double-layer effects. The surface concentration of the redox molecule and the change in driving force with changing applied potential are difficult to assess on bare electrodes. Electrodes with SAMs offer several elegant approaches to understanding the kinetic factors with minimized double layer effects. One of the key observations is that the transfer coefficient in the expression for the electrochemical rate constant is dependent on electrode potential in a predictable manner. Consequences of this behavior for more complex electron transfer processes (multiple electron transfers, electron transfers coupled with atom transfers) remain to be explored.

  Which of your professional achievements brings you the most satisfaction?

Publishing several key papers, including one of the first papers with the tunneling parameter for alkanethiol SAMs, one of the first papers showing that electronic coupling through the SAM could take place through alkane chains not directly connected with the redox center, and a paper showing that the rate of electron transfer was nearly independent of the metal. Also, writing a key review of SAMs on electrodes was satisfying.

Try to think of the experiments that address the fundamental questions in science.

Dr. Harry O. Finklea
West Virginia University
Department of Chemistry
Morgantown, WV, USA