Suppression of quantum oscillations and the dependence on site energies in electronic excitation transfer in the Fenna-Matthews-Olson trimer

TL;DR

This study models energy transfer in the FMO complex, revealing how site energies and initial excitation sites influence transfer dynamics and suppression of quantum oscillations, with implications for understanding photosynthetic efficiency.

Contribution

It provides a detailed theoretical analysis of energy transfer in the FMO complex considering all subunits and the eighth BChl, highlighting the impact of site energies and initial excitation sites.

Findings

Excitation at site 8 leads to slow exponential decay.

Excitation at sites 1 or 6 causes oscillations and faster transfer.

Variations in electronic transition energies significantly affect transfer dynamics.

Abstract

Energy transfer in the photosynthetic complex of the Green Sulfur Bacteria known as the Fenna-Matthews-Olson (FMO) complex is studied theoretically taking all three subunits (monomers) of the FMO trimer and the recently found eighth bacteriochlorophyll (BChl) molecule into account. We find that in all considered cases there is very little transfer between the monomers. Since it is believed that the eighth BChl is located near the main light harvesting antenna we look at the differences in transfer between the situation when BChl 8 is initially excited and the usually considered case when BChl 1 or 6 is initially excited. We find strong differences in the transfer dynamics, both qualitatively and quantitatively. When the excited state dynamics is initialized at site eight of the FMO complex, we see a slow exponential-like decay of the excitation. This is in contrast to the oscillations and a relatively fast transfer that occurs when only seven sites or initialization at sites 1 and 6 is considered. Additionally we show that differences in the values of the electronic transition energies found in the literature lead to a large difference in the transfer dynamics.