title: Elucidation of the timescales and origins of quantum electronic coherence in LHCII.
abstract: Photosynthetic organisms harvest sunlight with near unity quantum efficiency. The complexity of the electronic structure and energy transfer pathways within networks of photosynthetic pigment-protein complexes often obscures the mechanisms behind the efficient light-absorption-to-charge conversion process. Recent experiments, particularly using two-dimensional spectroscopy, have detected long-lived quantum coherence, which theory suggests may contribute to the effectiveness of photosynthetic energy transfer. Here, we present a new, direct method to access coherence signals: a coherence-specific polarization sequence, which isolates the excitonic coherence features from the population signals that usually dominate two-dimensional spectra. With this polarization sequence, we elucidate coherent dynamics and determine the overall measurable lifetime of excitonic coherence in the major light-harvesting complex of photosystem II. Coherence decays on two distinct timescales of 47 fs and ~800 fs. We present theoretical calculations to show that these two timescales are from weakly and moderately strongly coupled pigments, respectively.
authors.affiliation: Department of Chemistry, University of California, Berkeley, California 94720, USA.
authors.forename: Gabriela S
authors.initials: GS
authors.lastname: Schlau-Cohen
authors.forename: Akihito
authors.initials: A
authors.lastname: Ishizaki
authors.forename: Tessa R
authors.initials: TR
authors.lastname: Calhoun
authors.forename: Naomi S
authors.initials: NS
authors.lastname: Ginsberg
authors.forename: Matteo
authors.initials: M
authors.lastname: Ballottari
authors.forename: Roberto
authors.initials: R
authors.lastname: Bassi
authors.forename: Graham R
authors.initials: GR
authors.lastname: Fleming
mesh_terms: D004735:Energy Transfer; D006207:Half-Life; D045332:Photosystem II Protein Complex; D010860:Pigments, Biological; D013057:Spectrum Analysis
chemical_list: D045332:Photosystem II Protein Complex; D010860:Pigments, Biological