Electric Field Effects on Excited State and Electron Transfer Dynamics

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Professor Boxer of Stanford University will use Stark effect spectroscopy to investigate charge-transfer processes in simple molecules, with support from the Inorganic, Bioinorganic, and Organometallic Chemistry Program. The technique entails subjecting the sample (a thin film containing the molecule of interest) to a high and variable electric field, and observing the effect of the field on the absorption or emission of light. Characteristic lineshapes are obtained that yield information regarding the relationship between the transition dipole and the molecular axes. Processes to be investigated include LMCT transitions, intramolecular electron transfer reactions, proton transfer reactions, and vibrational transitions. Of particular interest is the influence of driving force on electron transfer rates. Molecules to be investigated include coordination complexes such as tris(bipyradyl)ruthenium(II) ion and related mixed-valence species, covalently-linked benzophenone/naphthalene derivatives, porphyrin/quinone species, certain rhenium complexes, and bromobenzene. This new technique should add an important new dimension in the understanding of molecular dynamics. %%% A particularly nettlesome problem is to understand the flow of charge within molecules. For example, if a molecule absorbs a photon of visible light, how do the electrons within the molecule respond spatially? Professor Boxer has developed a potentially powerful new technique, called Stark effect spectroscopy, to answer such questions. Essentially, the molecules are subjected to high electric fields while their interactions with light are measured. The results to be obtained will reveal how different parts of a molecule "communicate" and will improve understanding of the charge-separation processes so important in photosynthesis and related phenomena.