An investigation of medium effects on the one and two-dimensional electronic spectroscopy of chlorophyll a
The study of the photosynthetic processes has always had a particular relevance in spectroscopy because of its possible applications in light harvesting and energy storage. Since the light-harvesting pigment-protein complexes have this functional role in nature, many of studies have been focused on understanding photophysical processes occurring in these systems. Our work aims to study the spectroscopic properties of the best known pigment involved in the photosynthesis, Chlorophyll a, and their changes with different solvents. The study of the pigment was conducted by linear spectroscopic studies for water-solvent mixtures, while by the nonlinear technique 2D spectroscopy was applied for pure solvent. The theory and technique of 2D spectroscopy is described. The properties of solvents strongly influence the environment felt by the molecule and its capability of aggregate formation. The solvent properties that were found to be most relevant for our study were viscosity, H-bonding formation and polarity. While the first two were shown to be responsible for a persistent inhomogeneity in the 2D spectra, the kinetics of aggregate formation in water solvent mixtures were found to be influenced by the polarity and the capability of H bonding formation.
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