"This dissertation outlines the implementation of shaped femtosecond laser pulses to understand molecular dynamics as well as control their response with a temporally shaped electric field. The opening work focuses on using conventional time-resolved spectroscopic methods to understand excited state proton transfer dynamics using a Schiff base chromophore. The later studies describe the implementation of single beam based methods utilizing shaped femtosecond pulses to retrieve dynamical information from several cyanine dyes within the first 200 fs after the absorption of photons. The approach of shaping femtosecond pulses is applied to understand the dynamics of a set of cyanine dyes with various molecular polar responses as well as understanding the role a cyanine dye plays once placed inside human serum albumin protein. Lastly, the shaped pulses approach is applied to control both internal conversion from higher excited states in cyanines as well as the multiphoton ionization process of aromatic molecules. The first chapter provides a brief introduction on femtosecond laser spectroscopy and pulse shaping along with their use in understanding and controlling molecular dynamics on the ultrafast timescale. The second chapter focuses on using steady state and time-resolved spectroscopic methods to disentangle the dynamical steps during an excited state proton transfer from protic solvents to a Schiff base acting as a photobase. It was realized from steady state spectroscopic data that the Schiff base undergoes an increase in 14 pKa units upon excitation, which is the largest change in pKa units that has been reported for a photobase. The time-resolved studies reveal that the proton transfer process is initiated through the formation of a highly-polarized hydrogen bonding intermediate state within a timescale that is limited by the dielectric solvation constant. The third and fourth chapters discuss the application of programmable shaped femtosecond pulses to reveal dynamical information about the intramolecular response of substituted cyanines dyes. Changes in the molecular response, tracked through fluorescence or stimulated emission as a function of time delay between the spectral components of the excitation field, are related to the role of the substituent and its effect on the initial intramolecular energy relaxation soon after excitation. The role of binding indocyanine green inside the pocket of human serum albumin protein has been also investigated using the same approach in which it was revealed that the protein mitigates triplet state formation through hindering the twisting motion. The following two chapters expand on utilizing shaped pulses to control dynamical processes. In chapter 5, emission from the higher excited state, S2, is enhanced at the cost of suppressing internal conversion to the S1 state. This enhancement is achieved under strongly coupled excitation conditions using transform-limited pulses and can be tuned when excitation is carried out using chirped pulses. Lastly, chapter 6 summarizes the role of high order dispersion which results in the appearance of pre- and post-pulse pedestals that enhances the multiphoton ionization of toluene and p-nitrotoluene. In the final chapter a summary of the overall work is provided along with a future outlook and proposed experiments to be carried out are also discussed."--Pages ii-iii.
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