Physical origins and models of energy transfer in photosynthetic light-harvesting

Abstract

We perform a quantitative comparison of different energy transfer theories, i.e. modified Redfield, standard and generalized Förster theories, as well as combined Redfield-Förster approach. Physical limitations of these approaches are illustrated and critical values of the key parameters indicating their validity are found. We model at a quantitative level the spectra and dynamics in two photosynthetic antenna complexes: in phycoerythrin 545 from cryptophyte algae and in trimeric LHCII complex from higher plants. These two examples show how the structural organization determines a directed energy transfer and how equilibration within antenna subunits and migration between subunits are superimposed.

Light-harvesting and structural organization of Photosystem II: From individual complexes to thylakoid membrane

“…The results are qualitatively in agreement with those of Novoderezhkin et al [111,113] although there are several differences in exciton positions and peak amplitudes. Therefore, a new model was developed and the site energies were adjusted to give better agreement with the 2-D data.…”

Energy transfer dynamics in trimers and aggregates of light-harvesting complex II probed by 2D electronic spectroscopy

“…26 Regardless of the mechanism of dissipation, there is ample evidence that structural changes within the LHCII Chl energy transfer pathways and dynamics in the unquenched trimeric LHCII have been extensively studied using pump-probe spectroscopy. 5,[27][28][29] Similar dynamics of energy transfer were obtained in monomeric LHCII, indicating energy transfer processes within the monomeric subunits. 30 While pump-probe technique has been proven useful for studying Chl excited states, in the case of spatially unresolved Chl excitonic states, pump-probe spectroscopy alone cannot directly provide information on which Chl excitonic states are coupled.…”

Scalable High-Performance Algorithm for the Simulation of Exciton Dynamics. Application to the Light-Harvesting Complex II in the Presence of Resonant Vibrational Modes

“…57 The time-scale for the Chlb/Chla transfer obtained by both methods differs by one order of magnitude. 27,32,[34][35][36][37] The combined Förster-Redfield theory requires an empirical parameter M cr for separating the exciton Hamiltonian between a strongly coupled part H strong ex with all off-diagonal elements set to zero except those |J mn | > M cr and the remaining weakly coupled sites. 58 Suggested values for LHC II are M cr = 20 cm −1 or smaller.…”

“…58 Suggested values for LHC II are M cr = 20 cm −1 or smaller. 27,35 method is free of these restrictions and allows one to track the exciton-dynamics also through a network with the excitation emanating from a localized site. This initial condition is important for gaining insight into the physical mechanism underlying efficient transfer 15,59 and its relation to the spectral density.…”

“…10 Due to the lack of computational capabilities, energy-transfer in LHC II had been previously calculated only with approximate methods [32][33][34] with non-conclusive results for the transfer timescales. The predictions for the relaxation time differ by more than one order of magnitude 27,32,[35][36][37] from the results of Renger et al 34 Approximate methods work best in specific limits of delocalized (Redfield type) or incoherent dynamics (Förster transfer), or alternatively try to interpolate between the two cases. Any interpolation and combination of Förster/Redfield methods requires to introduce an empirical cut-off parameter, which depends on the precise system parameters (excitonic energies) as well as on the environment (temperature).…”