From Pulses to Pathways: Unveiling Molecular Motion and Energy Landscapes with 2D IR Spectroscopy
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Authors
Hassani, Majid
Issue Date
2025
Type
Dissertation
Language
en_US
Keywords
Chemical Physics
Alternative Title
Abstract
Two-dimensional infrared (2D IR) spectroscopy is a powerful technique for probing vibrational dynamics, including energy transfer, molecular interactions, and hydration dynamics, with ultrafast temporal resolution. By capturing spectral diffusion, vibrational coupling, and energy dissipation mechanisms, 2D IR provides direct insights into how molecular environments and structural modifications influence energy transport on femtosecond to picosecond timescales. This dissertation investigates the mechanisms governing vibrational energy redistribution and hydration dynamics in molecular systems using 2D IR spectroscopy coupled with vibrational probe methodologies. The role of Fermi resonance, i.e. strong anharmonic coupling, in directing vibrational thermal energy flow is explored using azido and cyano vibrational probes as reporters. Structural modifications, such as π-conjugation, steric constraints, and vibrational bottlenecks, were found to either facilitate or suppress energy transport. Heavy atom substitution, i.e. isotopic labeling, act as vibrational inhibitors, disrupting anharmonic pathways and enabling through-space dipole-dipole interactions to dominate. Additionally, my work examines the role of solvent viscosity and local solvation dynamics on spectral diffusion, revealing that frequency fluctuations of vibrational probes are dictated more by hydration shell structure than bulk solvent properties. Through a combination of experimental 2D IR measurements and molecular dynamics simulations, my study shows that second-shell solvent reorganization plays a dominant role in vibrational dephasing. By leveraging 2D IR spectroscopy, this dissertation provides new insights into the regulation of vibrational energy transport, solvent-mediated coupling, and tunable molecular interactions. These insights are further applied to probe catalytic behavior in Cu–peptide complexes, demonstrating how vibrational spectroscopy can guide the design of molecular systems with improved catalytic selectivity and reduced aggregation. These findings have broad implications for biomolecular spectroscopy, materials science, and the design of molecular systems with controlled energy flow.