Excitonic optical line shapes of trimers and tetramers: influence of dichotomous coloured transfer integral fluctuations

As most biological species, photosynthetic lifeforms have evolved to function optimally, despite thermal disorder and with fault tolerance. It remains a challenge to understand how this is achieved. To address this challenge the function of the protein-pigment complex photosystem I (PSI) of the cyanobacterium Synechococcus elongatus is investigated theoretically. The recently obtained high resolution structure of this complex exhibits an aggregate of 96 chlorophylls that are electronically coupled to function as a light-harvesting antenna complex. This paper constructs an effective Hamiltonian for the chlorophyll aggregate to describe excitation transfer dynamics and spectral properties of PSI. For this purpose, a new kinetic expansion method, the sojourn expansion, is introduced. Our study shows that at room temperature fluctuations of site energies have little effect on the calculated excitation lifetime and quantum yield, which compare favorably with experimental results. The efficiency of the system is found to be robust against 'pruning' of individual chlorophylls. An optimality of the arrangement of chlorophylls is identified through the quantum yield in comparison with an ensemble of randomly oriented chlorophylls, though, the quantum yield is seen to change only within a narrow interval in such an ensemble.

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“…For a discussion of dynamic disorder in a light-harvesting complex the reader is referred to Refs. [37,38].…”

Section: Random Matrix Theory As a Description Of Thermal Disordermentioning

confidence: 99%

Robustness and Optimality of Light Harvesting in Cyanobacterial Photosystem I

et al. 2002

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“…The two-state Markovian noise (or dichotomous noise) presents the archetype discrete state process which allows for an exact study of stochastically driven two-level quantum systems [40,[44][45][46][47][48][49][50]. Furthermore, the multistate case of an exciton transfer in molecular aggregates with many independent noise sources modeled by independent two-state Markovian noises is also solvable, in the sense that it can be reduced to solving numerically an algebraic relation [51]. This dichotomous noise can serve to model a pseudo-spin 1/2 stochastic bath degree of freedom.…”

Section: Introductionmentioning

confidence: 99%

Quantum two-state dynamics driven by stationary non-Markovian discrete noise: Exact results

Goychuk

Hänggi

2006

Chemical Physics

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We consider the problem of stochastic averaging of a quantum two-state dynamics driven by non-Markovian, discrete noises of the continuous time random walk type (multistate renewal processes). The emphasis is put on the proper averaging over the stationary noise realizations corresponding, e.g., to a stationary environment. A two-state non-Markovian process with an arbitrary non-exponential distribution of residence times (RTDs) in its states with a finite mean residence time provides a paradigm. For the case of a two-state quantum relaxation caused by such a classical stochastic field we obtain the explicit exact, analytical expression for the averaged Laplace-transformed relaxation dynamics. In the limit of Markovian noise (implying an exponential RTD), all previously known results are recovered. We exemplify new more general results for the case of non-Markovian noise with a biexponential RTD. The averaged, real-time relaxation dynamics is obtained in this case by numerically exact solving of a resulting algebraic polynomial problem. Moreover, the case of manifest non-Markovian noise with an infinite range of temporal autocorrelation (which in principle is not accessible to any kind of perturbative treatment) is studied, both analytically (asymptotic long-time dynamics) and numerically (by a precise numerical inversion of the Laplace-transformed averaged quantum relaxation).

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“…Such simulations have been used previously to model the optical response of polysilanes, 12,13 the temperaturedependent fluorescence 14 and transport 15 properties of J aggregates, and single molecular spectroscopy of circular aggregates. 16 Alternatively, stochastic models have been applied to describe the scattering of excitons on vibrations in disordered aggregates and the resulting spectral line shape 17,18 and relaxation dynamics. 19 In this paper, we report on a systematic theoretical study of dephasing of weakly localized Frenkel excitons in onedimensional systems, focusing on the effect of the scattering of the excitons on the vibrational modes ͑phonons͒ of the host.…”

Section: Introductionmentioning

confidence: 99%

Thermal broadening of the J-band in disordered linear molecular aggregates: A theoretical study

Heijs

Малышев

Knoester

2005

The Journal of Chemical Physics

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Take-down policy If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim.Downloaded from the University of Groningen/UMCG research database (Pure): http://www.rug.nl/research/portal. For technical reasons the number of authors shown on this cover page is limited to 10 maximum. We theoretically study the temperature dependence of the J-band width in disordered linear molecular aggregates, caused by dephasing of the exciton states due to scattering on vibrations of the host matrix. In particular, we consider inelastic one-and two-phonon scatterings between different exciton states ͑energy-relaxation-induced dephasing͒, as well as the elastic two-phonon scattering of the excitons ͑pure dephasing͒. The exciton states follow from numerical diagonalization of a Frenkel exciton Hamiltonian with diagonal disorder; the scattering rates between them are obtained using the Fermi golden rule. A Debye-type model for the one-and two-phonon spectral densities is used in the calculations. We find that, owing to the disorder, the dephasing rates of the individual exciton states are distributed over a wide range of values. We also demonstrate that the dominant channel of two-phonon scattering is not the elastic one, as is often tacitly assumed, but rather comes from a similar two-phonon inelastic scattering process. In order to study the temperature dependence of the J-band width, we simulate the absorption spectrum, accounting for the dephasing-induced broadening of the exciton states. We find a power-law ͑T p ͒ temperature scaling of the effective homogeneous width, with an exponent p that depends on the shape of the spectral density of the host vibrations. In particular, for a Debye model of vibrations, we find p Ϸ 4, which is in good agreement with the experimental data on J aggregates of pseudoisocyanine ͓I.

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Excitonic optical line shapes of trimers and tetramers: influence of dichotomous coloured transfer integral fluctuations

Cited by 12 publications

References 8 publications

Robustness and Optimality of Light Harvesting in Cyanobacterial Photosystem I

Robustness and Optimality of Light Harvesting in Cyanobacterial Photosystem I

Quantum two-state dynamics driven by stationary non-Markovian discrete noise: Exact results

Thermal broadening of the J-band in disordered linear molecular aggregates: A theoretical study

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