Vibrational and electronic spectroscopy, especially resonance Raman spectroscopy, for the study of electron transfer, solvent dynamics, chromophore aggregation, and solar photoconversion. Optical and electronic properties of nanomaterials and self-assembled dye aggregates, studies of interfacial electron transfer, optical and electronic properties of semiconductor nanoparticles. Light-harvesting plant pigments for solar energy conversion.

Prof. McHale received her Ph.D. in physical chemistry in 1979 from the University of Utah, where she worked with Prof. Jack Simons. She was a member of the chemistry faculty at the University of Idaho from 1980 until 2004, when she joined the chemistry faculty at Washington State University. She is a fellow in the American Association for the Advancement of Science and the author of Molecular Spectroscopy (Prentice-Hall, 1999). With co-editor Leah Bergman, she edited the recently published Handbook of Luminescent Semiconductor Materials (Taylor & Francis, 2011), available at www.crcpress.com/product/isbn/9781439834671;jsessionid=dp5DnB41uxcda3n54sQ-pg**

The McHale lab specializes in the use of resonance Raman and photoluminescence spectroscopy for the study of molecules and nanomaterials with interesting optical and electronic properties. Fundamental quantum mechanical aspects of electron transfer in solution and in interfacial systems are a major focus of our experiments. We pioneered the use of resonance Raman spectroscopy to study molecular aspects of solvent dynamics in electron transfer. Our current major research interests are the following.

Carrier Transport and Surface Properties of Metal Oxide Nanoparticles 

Our current research emphasis is on carrier transport and interfacial electron transfer in dye-sensitized solar cells (DSSCs). These novel photovoltaic cells are based on wide band gap semiconductors in nanoparticulate form, coated with visible-light absorbing dyes. DSSCs offer some potential advantages over the current silicon-based devices, but there are challenges to the realization of their environmental and economic advantages. We are using spectroelectrochemistry and novel preparations of nanocrystalline TiO₂ to understand the molecular basis for trap states which influence carrier mobilities and interfacial redox chemistry. We have recently begun to look at the defect chemistry of iron oxide nanoparticles with potential for solar water splitting.

Natural Plant Pigments for Solar Energy Conversion

We are also interested in finding alternatives to the expensive ruthenium-based dye sensitizers presently used in these solar cells, by exploring natural dyes from plants and flowers as potential sensitizers in solar photoconversion. We have recently explored a new class of plant pigments, called betalains, with much potential for pushing the efficiency of natural dye-based solar cells to higher values.

 Biomimetic Light-Harvesting Aggregates

Dyes which absorb visible light strongly often have a tendency to self-aggregate, which can alter the optical and electronic properties. We are interested in the unique optical properties of the self-assemblies of water-soluble porphyrins. We are uncovering the molecular details which determine the hierarchal structure of these aggregates, and the nature of the intermolecular forces and excitonic couplings which lead to delocalized excited electronic states.  Our long range goal  is to control and exploit the hierarchal structure of light-harvesting aggregates to improve the efficiency of dye-based solar energy conversion.

Prof. McHale recently contributed a chapter, "Hierarchal Structure of Light-Harvesting Porphyin Aggregates," to Vol. 2 of J-Aggregates, edited by T. Kobayashi and published by World Scientific Press, available at www.worldscibooks.com/materialsci/8226.html

To see a video about our recent work on hierarchal light-harvesting aggregates, please visit www.youtube.com/watch.