Nonlinear Spectroscopy in Chlorophyll Dimers Embedded in an Asymmetric Phonon Bath.

Area of Science:

• Quantum Biology
• Spectroscopy
• Biophysics

Background:

• Photosynthetic complexes utilize intricate pigment-protein interactions for efficient energy transfer.
• Understanding exciton-phonon coupling is key to elucidating these energy transfer mechanisms.
• Existing models often simplify the spectral density of phonons, limiting accuracy.

Purpose of the Study:

• To develop a novel 4-point time correlation function for electronic transition dipole moments in dimeric photosynthetic complexes.
• To incorporate experimentally fit spectral densities, including asymmetric phonon-sidebands, into theoretical models.
• To provide a computationally tractable method for analyzing nonlinear optical signals and exciton-phonon coupling.

Main Methods:

• Calculation of the 4-point time correlation function for the electronic transition dipole moment.
• Utilizing an experimentally determined spectral density of photosynthetic phonons.
• Modeling the asymmetric phonon-sideband and its impact on optical signals.
• Accounting for both excitonic and exciton-phonon couplings within Liouville space pathways.

Main Results:

• The developed method accurately captures the asymmetry in phonon-sidebands, arising from unequal phonon contributions.
• The 4-point time correlation function explicitly reflects the spectral connection between phonon-sidebands and the 1-phonon profile.
• The approach allows for fine-tuning of electron-phonon coupling and modeling of bath symmetry.

Conclusions:

• The 4-point time correlation function offers a convenient, tractable, and computationally expedient tool for studying complex photosynthetic systems.
• This method provides deeper insights into exciton-phonon coupling strength and phonon relaxation mechanisms.
• It enables accurate characterization of pigment-protein interactions and energy transfer dynamics.