Title: Ultrafast energy relaxation in single light-harvesting complexes

Abstract

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. Lastly,more » our findings thus agree with the commonly used notion of an ensemble of identical LH2 complexes experiencing slow random fluctuations.« less

Authors:

Malý, Pavel ^[1]; Gruber, J. Michael ^[2]; Cogdell, Richard J. ^[3]; Mančal, Tomáš ^[4]; van Grondelle, Rienk ^[2]

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+ Show Author Affiliations

1. Department of Physics and Astronomy, Faculty of Sciences, Vrije Universiteit Amsterdam, 1081HV Amsterdam, The Netherlands,, Institute of Physics, Faculty of Mathematics and Physics, Charles University in Prague, 121 16 Prague, Czech Republic,
2. Department of Physics and Astronomy, Faculty of Sciences, Vrije Universiteit Amsterdam, 1081HV Amsterdam, The Netherlands,
3. Institute of Molecular, Cellular and Systems Biology, College of Medical, Veterinary and Life Sciences, University of Glasgow, Glasgow G128QQ, United Kingdom
4. Institute of Physics, Faculty of Mathematics and Physics, Charles University in Prague, 121 16 Prague, Czech Republic,

Publication Date:

2016-02-22

Research Org.:

Energy Frontier Research Centers (EFRC) (United States). Photosynthetic Antenna Research Center (PARC)

Sponsoring Org.:

USDOE Office of Science (SC), Basic Energy Sciences (BES)

OSTI Identifier:

1238807

Alternate Identifier(s):

OSTI ID: 1387502

Grant/Contract Number:  

SC0001035

Resource Type:

Published Article

Journal Name:

Proceedings of the National Academy of Sciences of the United States of America

Additional Journal Information:

Journal Name: Proceedings of the National Academy of Sciences of the United States of America Journal Volume: 113 Journal Issue: 11; Journal ID: ISSN 0027-8424

Publisher:

Proceedings of the National Academy of Sciences

Country of Publication:

United States

Language:

English

Subject:

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; solar (fuels); photosynthesis (natural and artificial); biofuels (including algae and biomass); bio-inspired; charge transport; membrane; synthesis (novel materials); synthesis (self-assembly)