Electric Field Effects on Excited State and Electron Transfer Dynamics

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This award by the Inorganic, Bioinorganic and Organometallic Chemistry program supports research by Professor Stephen G. Boxer of Stanford University to continue studies on the development of spectroscopic methods that probe interactions between molecular fragments separated by relatively long spacer groups. Stark effect spectroscopy is used to provide quantitative information on the magnitude and direction of charge displacement associated with a spectroscopic transition. The effect of an applied electric field on an electronic or vibrational transition is used to generate a deeper understanding of bonding, especially in coordination complexes, and the concept that the vibrational frequency shifts can be a quantitative probe for electrostatic effects in complex systems such as proteins. Initial results indicate that vibrational Stark spectroscopy can be a powerful and minimally invasive approach for obtaining information on how protein electrostatic fields change in modified proteins and during catalysis. This work begins to outline how electric fields can be used to manipulate the rates of electron and proton transfer as biochemical reactions create, consume or displace electric dipoles. Unusual and characteristic non-classical Stark effects are expected to occur in mixed-valence complexes that exhibit multiple states whose energy difference is affected by the applied field. Analyses of the resulting unusual line shapes will give quantitative information on the energetics, electronic coupling and charge displacement in these molecules.A new form of spectroscopy will be used to study how electric fields affect electron, proton and dipole movements in chemical, photochemical and biochemical processes.