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. 2002 Feb;82(2):1030–1039. doi: 10.1016/S0006-3495(02)75462-3

Excitonic coupling of chlorophylls in the plant light-harvesting complex LHC-II.

Axel Schubert 1, Wichard J D Beenken 1, Holger Stiel 1, Bernd Voigt 1, Dieter Leupold 1, Heiko Lokstein 1
PMCID: PMC1301909  PMID: 11806942

Abstract

Manifestation and extent of excitonic interactions in the red Chl-absorption region (Q(y) band) of trimeric LHC-II were investigated using two complementary nonlinear laser-spectroscopic techniques. Nonlinear absorption of 120-fs pulses indicates an increased absorption cross section in the red wing of the Q(y) band as compared to monomeric Chl a in organic solution. Additionally, the dependence of a nonlinear polarization response on the pump-field intensity was investigated. This approach reveals that one emitting spectral form, characterized by a 2.3(+/-0.8)-fold larger dipole strength than monomeric Chl a, dominates the fluorescence spectrum of LHC-II. Considering available structural and spectroscopic data, these results can be consistently explained assuming the existence of an excitonically coupled dimer located at Chl-bindings sites a2 and b2 (referring to the original notation of W. Nühlbrandt, D.N. Wang, and Y. Fujiyoshi, Nature, 1994, 367:614-621), which must not necessarily correspond to Chls a and b). This fluorescent dimer, terminating the excitation energy-transfer chain of the LHC-II monomeric subunit, is discussed with respect to its relevance for intra- and inter-antenna excitation energy transfer.

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Selected References

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