Probing energy transfer events in the light harvesting complex 2 (LH2) of Rhodobacter sphaeroides with two-dimensional spectroscopy

Excitation energy transfer events in the photosynthetic light harvesting complex 2 (LH2) of Rhodobacter sphaeroides are investigated with polarization controlled two-dimensional electronic spectroscopy. A spectrally broadened pulse allows simultaneous measurement of the energy transfer within and be...

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Bibliographic Details
Published in:The Journal of chemical physics 2013-10, Vol.139 (15), p.155101-155101
Main Authors: Fidler, Andrew F, Singh, Ved P, Long, Phillip D, Dahlberg, Peter D, Engel, Gregory S
Format: Article
Language:English
Subjects:
ABSORPTION
Biological Molecules and Networks
ENERGY TRANSFER
EXCITATION
EXCITED STATES
INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY
INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND TECHNOLOGY
Light-Harvesting Protein Complexes - chemistry
Light-Harvesting Protein Complexes - isolation & purification
Models, Molecular
MOLECULAR STRUCTURE
OPTICAL MICROSCOPY
POLARIZATION
PULSES
RELAXATION
Rhodobacter sphaeroides - chemistry
SPECTRA
SPECTROSCOPY
Spectrum Analysis
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Summary:Excitation energy transfer events in the photosynthetic light harvesting complex 2 (LH2) of Rhodobacter sphaeroides are investigated with polarization controlled two-dimensional electronic spectroscopy. A spectrally broadened pulse allows simultaneous measurement of the energy transfer within and between the two absorption bands at 800 nm and 850 nm. The phased all-parallel polarization two-dimensional spectra resolve the initial events of energy transfer by separating the intra-band and inter-band relaxation processes across the two-dimensional map. The internal dynamics of the 800 nm region of the spectra are resolved as a cross peak that grows in on an ultrafast time scale, reflecting energy transfer between higher lying excitations of the B850 chromophores into the B800 states. We utilize a polarization sequence designed to highlight the initial excited state dynamics which uncovers an ultrafast transfer component between the two bands that was not observed in the all-parallel polarization data. We attribute the ultrafast transfer component to energy transfer from higher energy exciton states to lower energy states of the strongly coupled B850 chromophores. Connecting the spectroscopic signature to the molecular structure, we reveal multiple relaxation pathways including a cyclic transfer of energy between the two rings of the complex.
ISSN:0021-9606
1089-7690
DOI:10.1063/1.4824637