Quantum coherences, or beats, observed in ultrafast optical experiments arise when light-matter interactions from a coherent source drive a system out of thermal equilibrium.  The dynamcis of these coherences can provide insights into the Hamiltonian underlying the energy transfer processes of photosynthetic pigment-protein complexes. Recent work has shown that redox conditions affect the ultrafast energy transfer dynamcis in the Fenna-Matthews-Olson pigment-protein complex in green sulfur bacteria. Here we present ultrafast two-dimensional electronic spectroscopy measurements on the Fenna-Matthews-Olson antenna complex under both oxidizing and reducing conditions. We observe many excited state coherences present in reducing conditions, which more closely mimic the natural conditions of the complex, are absent or attenuated in oxidizing conditions. Further, the presence of these coherences is correlated with increased vibronic coupling in the system and faster, more efficient energy transfer through the complex.

Investigating the effect of redox conditions on quantum beats in 2D electronic spectra of the FMO complex

ACS Fall 2021

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