We are interested systems in which electron transfer and electronic coupling play an integral role. Both fundamental and applied projects involving electron transfer are pursued and these involve both the synthesis (chemical or material) of new systems as well as their characterization. The characterization employed is wide-ranging involving UV-vis, IR, NMR, Raman, and time-resolved spectroscopy in addition to techniques like AFM and STM. Below are a few examples of the types of question in which we are interested.
Electron transfer for solar energy capture
Increasing the efficiency of dye-sensitized solar cells by exploiting molecular symmetry
In dye-sensitized solar cells, a dye molecule is excited by the absorption of an electron and this is followed by transfer of the excited state electron to an electrode and the remaining hole to a different electrode. This generates an electric potential between these electrodes that may be utilized later for performing useful work. An obvious requirement for this cell is that the hole and electrode must be transferred to different electrodes. Differentiation in electron and hole transfer pathways is typically accomplished by resorting to large thermodynamic driving forces that reduce the overall efficiency of the solar cell. We are interested in exploiting symmetry considerations to bias the electron- and hole-transfers from excited dye molecules towards the electrodes of interest. This, in effect, results in intelligent manipulation of the electronic coupling pathways for electron and hole transport and allows for bias of these pathways in the absence of large driving forces, increasing the overall efficiency of the cell. We are interested in developing these dyes, studying their fundamental photo-physical properties, and incorporating them into working solar cells.
Exerting fine control over conduction through individual molecules
Nanoscience has brought with it many promises of new technology. One of the most fascinating of these is the promise of molecular electronics – in which analogs of conventional electronics are constructed out of individual molecules. In order to build such devices, understanding conductance through individual molecules becomes critical. Moreover, it would be useful to achieve dynamic fine-tuning of the electrical conductance through these molecules. We are interested in developing new ways in which to realize this fine-tuning of conductance. Our approach relies on non-covalent interactions that will form the platform for reversible doping of conducting molecules and we look towards there use in constructing workable molecular devices, such as molecular sensors.
Dynamics of electronic coupling
Understanding the fundamental rate of molecular computation
In the case that we wish to construct a molecular computer, it becomes important to ask what is the timescale associated with switching between conducting and insulating states of molecules. This is identical to inquiring after the fundamental clock rate of molecular computers. In order to address this question, we investigate the timescale of electronic coupling in model systems that employ mixed valence complexes. These complexes are defined as molecules that have two degenerate electronic ground states that may be exchanged by the exchange of an electron. The two degenerate electronic states may couple with one another and we wish to probe the rate at which this coupling occurs following the generation of the mixed valence state. By attaching a photo-sensitizer to a mixed valence pre-curser, we may quickly and coherently generate a population of mixed valence complexes. Observing the subsequent evolution of markers associated with electronic coupling allows for determination of the fundamental rate of electronic coupling for these molecular systems.