Ultrafast pump-probe spectroscopy of bacteriochlorophyll c antennae in bacteriochlorophyll a-containing chlorosomes from the green photosynthetic bacterium Chloroflexus aurantiacus

Su Lin, Herbert Van Amerongen, Walter S. Struve

Research output: Contribution to journalArticle

45 Scopus citations

Abstract

Time-dependent isotropic and anisotropic absorption difference profiles have been obtained with 2 ps resolution for the (BChl) bacteriochlorophyll c antenna in BChl a-containing chlorosomes from the green photosynthetic bacterium Chloroflexus aurantiacus. The isotropic absorption difference spectra are bipolar; they are dominated by excited state absorption at wavelengths < 725 nm, and by ground state photobleaching at wavelengths > 735 nm. The entire isotropic spectrum exhibits a dynamic blue shift over approx. 4 nm with a time constant of approx. 7 ps. All of these phenomena are rationalized in terms of a linear exciton model that resembles the theory of J-aggregates. In this theory, the occurrence of the dynamic blue shift corresponds to relaxation between Qy excitation components; it cannot readily be explained using a model that assumes that the excitations are localized on single chromophores within 1 ps. The anisotropic decay times, resolved here for the first time with our 2 ps fwhm instrument function, are approx. 7 ± 1 ps at 720 nm and 4 ± 1 ps at 740 nm. The residual anisotropy r(∞) is 0.32 ± 0.02 at 740 nm, which is in good agreement with fluorescence and linear dichroism measurements. These anisotropy functions initialize to 0.4 within error, indicating that subpicosecond depolarization is not prevalent.

Original languageEnglish (US)
Pages (from-to)13-24
Number of pages12
JournalBBA - Bioenergetics
Volume1060
Issue number1
DOIs
StatePublished - Sep 27 1991
Externally publishedYes

Keywords

  • (C. aurantiacus)
  • Antenna
  • Bacterial photosynthesis
  • Bacteriochlorophyll
  • Chlorosome
  • Pump-probe spectroscopy
  • Ultrafast spectroscopy

ASJC Scopus subject areas

  • Biophysics
  • Biochemistry
  • Cell Biology

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