Femtosecond Multidimensional Electronic and Raman Spectroscopy towards the Study of Mn Complexes and the Oxygen Evolving Complex: Developing Understanding of Femtosecond Light Generation and Applying Femtosecond Multidimensional Electronic and Raman Spectroscopies to Model Systems.

摘要

The oxygen evolving complex of photosystem II is a tetramanganese complex that catalyzes the oxidation of water to dioxygen. Many experimental methods have been employed to study this complex, including a variety of spectroscopic methods. The complexity of the surrounding protein environment challenges reliable interpretation of the spectral features and discrimination between changes in the complex and the many cofactors of photosystem II. We have proposed coherent multidimensional spectroscopy in the mixed time-/frequency-domain as a strategy for exploring the spectroscopy of this important system. Coherent multidimensional spectroscopy is performed by the temporal synchronization and spatial overlap of a sequence of fields to induce a polarization in the material. The fields induced by polarizations meeting certain energy- and momentum-criteria are sampled; the intensity of the fields as functions of frequency and time elucidate the spectral and temporal characteristics of the sample's quantum states. Here, we describe efforts to extend the spectroscopy of model transition metal complexes to the femtosecond regime. We present the implementation of white-light transient absorption and demonstrate our ability to reproduce the spectroscopic behavior of manganese (III) tetraphenylporphine with improved time resolution over previously published results; we discuss the limitations encountered when extending this spectroscopy to homodyne-detected transient grating methods. We have implemented a strategy for broadband coherent anti-Stokes Raman spectroscopy, showing the results of these efforts. A theoretical background into the pulse propagation effects in the ultrafast regime of femtosecond spectroscopy has been compiled. We have found these propagation effects to have profound importance in the tuning and amplification of femtosecond pulses, and we present the results of simulations exploring how these effects manifest and influence the behavior of a particular process employed in light generation in a commercial traveling-wave optical parametric amplifier.