Ultrafast energy relaxation in single light-harvesting complexes

Malý, P., Gruber, J. M., Cogdell, R. J. , Mančal, T. and van Grondelle, R. (2016) Ultrafast energy relaxation in single light-harvesting complexes. Proceedings of the National Academy of Sciences of the United States of America, 113(11), pp. 2934-2939. (doi: 10.1073/pnas.1522265113) (PMID:26903650) (PMCID:PMC4801264)

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Energy relaxation in light-harvesting complexes has been extensively studied by various ultrafast spectroscopic techniques, the fastest processes being in the sub–100-fs range. At the same time, much slower dynamics have been observed in individual complexes by single-molecule fluorescence spectroscopy (SMS). In this work, we use a pump–probe-type SMS technique to observe the ultrafast energy relaxation in single light-harvesting complexes LH2 of purple bacteria. After excitation at 800 nm, the measured relaxation time distribution of multiple complexes has a peak at 95 fs and is asymmetric, with a tail at slower relaxation times. When tuning the excitation wavelength, the distribution changes in both its shape and position. The observed behavior agrees with what is to be expected from the LH2 excited states structure. As we show by a Redfield theory calculation of the relaxation times, the distribution shape corresponds to the expected effect of Gaussian disorder of the pigment transition energies. By repeatedly measuring few individual complexes for minutes, we find that complexes sample the relaxation time distribution on a timescale of seconds. Furthermore, by comparing the distribution from a single long-lived complex with the whole ensemble, we demonstrate that, regarding the relaxation times, the ensemble can be considered ergodic. Our findings thus agree with the commonly used notion of an ensemble of identical LH2 complexes experiencing slow random fluctuations.

Item Type:Articles
Additional Information:ACKNOWLEDGMENTS. P.M., J.M.G., and R.v.G. were supported by Vrije Universiteit and by Advanced Investigator Grant 267333 (PHOTPROT) from the European Research Council (to R.v.G.); R.v.G. was also supported by the Nederlandse Organisatie voor Wetenschappelijk Onderzoek, Council of Chemical Sciences, via TOP Grant 700.58.305, and by the EU FP7 Project PAPETS (GA 323901). R.v.G. gratefully acknowledges his Academy Professor grant from the Netherlands Royal Academy of Sciences. P.M. and T.M. received financial support from Czech Science Foundation Grant 14-25752S. R.J.C. was supported as part of the Photosynthetic Antenna Research Center, an Energy Frontier Research Center funded by the US Department of Energy, Office of Science, Basic Energy Sciences, under Award DE-SC0001035.
Glasgow Author(s) Enlighten ID:Cogdell, Professor Richard
Authors: Malý, P., Gruber, J. M., Cogdell, R. J., Mančal, T., and van Grondelle, R.
College/School:College of Medical Veterinary and Life Sciences > Institute of Molecular Cell and Systems Biology
Journal Name:Proceedings of the National Academy of Sciences of the United States of America
Publisher:National Academy of Sciences
ISSN (Online):1091-6490

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Project CodeAward NoProject NamePrincipal InvestigatorFunder's NameFunder RefLead Dept
502612Photosynthetic Antenna Research Center (PARC)Richard CogdellUS Department of Energy (DEN)DE-SC0001035RI MOLECULAR CELL & SYSTEMS BIOLOGY