Role of Coherence in Excitation Transfer Efficiency to the Reaction Center in Photosynthetic Bacteria Chlorobium tepidum

Abstract

We investigate the effect of coherence to the excitation transfer efficiency (ETE) in photosynthetic bacteria Chlorobium tepidum. We have modelled the monomer of Fenna‐Matthews‐Olson (FMO) complex as consisting of eight bacteriochlorophyll‐a sites, while explicitly consider reaction center core complex (RCC) as an additional site. With the use of realistic bath spectrum and several dominant vibronic modes in the non‐Markovian master equation, in an effective 9‐site model, we have compared the ETE for an initial pure state and an initial mixed state. We observe that the initial pure state relaxes efficiently to increase the trapping at the RCC. We further illustrate that the coherence play a competitive role to block the back transfer of excitation from RCC pigment to FMO complex and hence to maximize the ETE.

Importance of Intermonomer Couplings of the FMO Complex in Coherently Initiated Dynamics

“…The experimental observations using time-resolved absorption and fluorescence spectroscopy shows that, in the energetically connected FMO-RCC complexes, 76% excitation moves from the FMO to RCC . To confirm the experimental observation using the HEOM approach, we considered the following initial pure state (obtained by the interaction of femtosecond laser pulse with FMO complex): …”

“…It implies that, under in vivo conditions, energy transfers via all the monomers of the FMO to RCC, as the adjacent monomers have nonzero intermonomer couplings . However, in the theoretical studies, it has been assumed that the excitation moves almost independently via each monomer to the RCC. ,,,− The assumption is considered without the explicit study of the role of the intermonomer couplings, which implies that the detailed study of the affect of the intermonomer couplings on the excitation transfer dynamics is urgently required.…”

Coherent Speedup of Excitation Energy Transfer in PC645

“…The noisy physiological environment had been hypothesized to quickly dephase the coherence, which led to the discrete hopping (instead of coherent delocalization) of excitation between the pigments . However, recent spectroscopic observations of the EET in PPCs indicate the existence of the quantum coherence for the relevant time scales of the EET. − Following this, various theoretical models − were developed to study the role of quantum coherence in the EET. − Still, the relevance of quantum coherence in the EET is controversial.…”