The nature of coherences in the B820 bacteriochlorophyll dimer revealed by two-dimensional electronic spectroscopy

Marco Ferretti, Vladimir I. Novoderezhkin, Elisabet Romero, Ramunas Augulis, Anjali Pandit, Donatas Zigmantas, Rienk van Grondelle

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Light-harvesting in photosynthesis is determined by the excitonic interactions in disordered antennae and the coupling of collective electronic excitations to fast nuclear motions, producing efficient energy transfer with a complicated interplay between exciton and vibrational coherences. Two-dimensional electronic spectroscopy (2DES) is a powerful tool to study the presence of these coherences in photosynthetic complexes. However, the unambiguous assignment of the nature of the observed coherences is still under debate. In this paper we apply 2DES to an excitonically coupled bacteriochlorophyll dimer, the B820 subunit of the light harvesting complex 1 (LH1-RC) of R. rubrum G9. Fourier analysis of the measured kinetics and modeling of the spectral responses in a complete basis of electronic and vibrational states allow us to distinguish between pure vibrational, mixed exciton-vibrational (vibronic), and predominantly exciton coherences. The mixed coherences have been found in a wide range of oscillation frequencies, whereas exciton coherences give the biggest contributions for the frequencies in the 400-550 cm(-1) range, corresponding to the exciton splitting energy of the B820 dimer. Significant exciton coherences are also present at higher frequencies, i.e., up to 800 cm(-1), which are determined by realizations of the disorder with a large energy gap between the two pigments (which increases the apparent value of the exciton splitting). Although the B820 dimer is a model system, the approach presented here represents a basis for further analyses of more complicated systems, providing a tool for studying the interplay between electronic and vibrational coherences in disordered photosynthetic antennae and reaction centres.
Original languageEnglish
Pages (from-to)9930-9939
JournalPhysical Chemistry Chemical Physics
Issue number21
Publication statusPublished - 2014

Bibliographical note

The information about affiliations in this record was updated in December 2015.
The record was previously connected to the following departments: Chemical Physics (S) (011001060)

Subject classification (UKÄ)

  • Atom and Molecular Physics and Optics


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