Two-Dimensional Electronic Spectroscopy of Chlorophyll a: Solvent Dependent Spectral Evolution

Area of Science:

• Photochemistry
• Spectroscopy
• Biophysics

Background:

• Chlorophyll is the primary chromophore in light harvesting complexes, crucial for energy transfer.
• Protein environments fine-tune chlorophyll electronic transitions for optimized energy transfer.
• Understanding solvent effects on monomeric chlorophyll is vital for comprehending these processes.

Purpose of the Study:

• Investigate the interaction between monomeric chlorophyll's Q-band electronic transition and solvents.
• Characterize solvent-induced spectral diffusion and reorganization effects.
• Determine the influence of solvent physical-chemical properties on chlorophyll electronic transitions.

Main Methods:

• Two-dimensional electronic spectroscopy (2DES) was employed to study monomeric chlorophyll.
• Analysis utilized a Brownian oscillator model to interpret spectral dynamics.
• Absorption spectra and Stokes shifts were calculated and compared.

Main Results:

• Q-band 2DES exhibited significant inhomogeneous broadening, persisting over nanosecond timescales.
• Spectral reshaping occurred across multiple timescales, primarily attributed to spectral diffusion.
• Inhomogeneous broadening was solvent-dependent, increasing in hydrogen-bonding and viscous solvents.
• Fastest spectral reshaping components were linked to solvent dynamics interacting with chlorophyll.

Conclusions:

• Solvent properties profoundly impact monomeric chlorophyll's electronic transitions and spectral dynamics.
• The observed spectral diffusion and reorganization effects are strongly modulated by solvent interactions.
• This research provides insights into the environmental factors governing light-harvesting processes.