Influence of intra-pigment vibrations on dynamics of photosynthetic exciton

Abstract

We have numerically investigated the effect of an underdamped intra-pigment vibrational mode on an exciton's quantum coherence and energy transfer efficiency. Our model describes a bacteriochlorophyll a pigment-protein dimer under the conditions at which photosynthetic energy transfer occurs. The dimer is modeled using a theoretical treatment of a vibronic exciton, and its dynamics are numerically analyzed using a non-Markovian and non-perturbative method. We examined the system's response to various values of the Huang-Rhys factor, site energy difference, reorganization energy, and reorganization energy difference. We found that the inclusion of the intra-pigment vibronic mode allows for long-lived oscillatory quantum coherences to occur. This excitonic coherence is robust against static site-energy disorder. The vibrational mode also promotes exciton transfer along the site-energy landscape thus improving the overall energy transfer efficiency.

Effect of an underdamped vibration with both diagonal and off‐diagonal exciton–phonon interactions on excitation energy transfer

“…and correctly capture the essence of the type‐A regime. It is noted that the reorganization‐energy dependence of the resonant frequency has also been reported in previous work …”

“…It is instructive to reinspect a special case that the exciton–phonon interaction is only in the diagonal term, that is, φ = 0, which has been broadly investigated, though, under an independent bath model . It can be proved (see Ref.…”

“…The well‐designed experiments on the photosystem II reaction center, light‐harvesting complex II, cryptophyte light‐harvesting protein PC645 and conjugated polymers have shown the vibronic natures of the observed long‐lasting coherent dynamics and have demonstrated their tight connections to the ultrafast EET and charge separation processes. Theoretically, various calculations have confirmed the existence of resonant vibration‐assisted ultrafast carrier dynamics, and the resonant frequency has been demonstrated to be relevant to the reorganization energy . The synergistic effect of multiple underdamped vibrations has also been reported .…”

“…One of possible origins is the vibronic coherence from the interactions between the exciton and underdamped vibrations as the vibrational frequencies are resonant with the excitonic energy gap, first proposed by Christensson et al From then on, more and more attentions have been paid on the role of these vibrations on the beating signals as well as the corresponding carrier dynamics. It is now accepted that the underdamped vibrations with resonant frequencies may facilitate the EET, charge separation and singlet fission, which have largely extended the knowledge about resonant vibration‐assisted carrier dynamics. Along this way, various fascinating results have been obtained.…”

Vibrationally assisted quantum energy pumps

“…While recent experiments indicate an important role for vibrations in exciton transport [11][12][13], most theoretical investigations consider the effects of weakly coupled vibrational dynamics through the environment for the exciton dynamics [14][15][16][17][18][19][20][21][22]. Others consider the case when a single vibrational mode is globally coupled to the excitons in an exciton-vibronic Hamiltonian [23][24][25][26]. However, investigation into directed charge transport such as the recent models of [22,27], make the assumption of an overall 'downhill' spatial bias in the molecular energies or require noise to achieve transport directionality.…”