Welcome to Cather Simpson's Research Group Website!

Photochemistry in Important Molecules.

We explore the dynamic (and dramatic!) events immediately after the photoexcitation of large bio-molecules in solution. Our state-of-the-art laser systems monitor the intramolecular (IVR) and intermolecular (VR) energy flow as the excited molecule evolves in femtoseconds to nanoseconds. This challenging and exciting research will help us to understand ultrafast dynamics and the structural and environmental influences upon them. The insight we gain will be used to run chemistry with light.

We investigate two classes of molecules: porphyrins and stilbene-type systems. Porphyrins catalyze a range of crucial biological reactions and are vital components of modern technology (e.g. fuel cells, molecular electronics) Their natural properties place them in pivotal roles as future catalysts designed to perform selected tasks. Stilbene is the prototype for photoisomerization and is a building block for many polymers. Diphosphenes are fascinating new stilbene analogs with P=P double bonds. Diphosphenes do many remarkable photo-induced reactions. They hold much promise for use in conducting and light-emitting polymers.

Other research focuses upon making very accurate classical force fields for large molecules. Generic force fields (e.g. MMX, Amber, UFF) are widely useful but have only limited use for detailed studies of structure-spectrum behavior. Quantum mechanical methods are more accurate but also more expensive. We have improved a method that merges ab initio accuracy with classical efficiency. We first explored porphyrins and the initial results have been highly successful. Work is in progress on other systems.