Dynamics of exciton relaxation in LH2 antenna probed by multipulse nonlinear spectroscopy

J Phys Chem A. 2011 Apr 28;115(16):3834-44. doi: 10.1021/jp108187m. Epub 2011 Jan 26.

Abstract

We explain the relaxation dynamics in the LH2-B850 antenna as revealed by multipulse pump-dump-probe spectroscopy (Th. A. Cohen Stuart, M. Vengris, V. I. Novoderezhkin, R. J. Cogdell, C. N. Hunter, R. van Grondelle, submitted). The theory of pump-dump-probe response is evaluated using the doorway-window approach in combination with the modified Redfield theory. We demonstrate that a simultaneous fit of linear spectra, pump-probe, and pump-dump-probe kinetics can be obtained at a quantitative level using the disordered exciton model, which is essentially the same as used to model the spectral fluctuations in single LH2 complexes (Novoderezhkin, V.; Rutkauskas, D.; van Grondelle, R. Biophys. J. 2006, 90, 2890). The present studies suggest that the observed relaxation rates are strongly dependent on the realization of the disorder. A big spread of the rates (exceeding 3 orders of magnitude) is correlated with the disorder-induced changes in delocalization length and overlap of the exciton wave functions. We conclude that the bulk kinetics reflect a superposition of many pathways corresponding to different physical limits of energy transfer, varying from sub-20 fs relaxation between delocalized and highly spatially overlapping exciton states to >20 ps jumps between states localized at the opposite sides of the ring.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Bacterial Proteins / chemistry*
  • Kinetics
  • Light-Harvesting Protein Complexes / chemistry*
  • Models, Chemical
  • Rhodopseudomonas / chemistry
  • Spectrum Analysis
  • Thermodynamics*

Substances

  • B800-850 light-harvesting complex, bacteria
  • Bacterial Proteins
  • Light-Harvesting Protein Complexes