title: Ultrafast infrared observation of exciton equilibration from oriented single crystals of photosystem II.
abstract: In oxygenic photosynthesis, two photosystems work in series. Each of them contains a reaction centre that is surrounded by light-harvesting antennae, which absorb the light and transfer the excitation energy to the reaction centre where electron transfer reactions are driven. Here we report a critical test for two contrasting models of light harvesting by photosystem II cores, known as the trap-limited and the transfer-to-the trap-limited model. Oriented single crystals of photosystem II core complexes of Synechococcus elongatus are excited by polarized visible light and the transient absorption is probed with polarized light in the infrared. The dichroic amplitudes resulting from photoselection are maintained on the 60 ps timescale that corresponds to the dominant energy transfer process providing compelling evidence for the transfer-to-the-trap limitation of the overall light-harvesting process. This finding has functional implications for the quenching of excited states allowing plants to survive under high light intensities.
authors.affiliation: Imperial College London, South Kensington Campus, Sir Ernst Chain Building, London SW7 2AZ, UK.
authors.forename: Marius
authors.initials: M
authors.lastname: Kaucikas
authors.affiliation: Imperial College London, South Kensington Campus, Sir Ernst Chain Building, London SW7 2AZ, UK.
authors.forename: Karim
authors.initials: K
authors.lastname: Maghlaoui
authors.affiliation: Imperial College London, South Kensington Campus, Sir Ernst Chain Building, London SW7 2AZ, UK.
authors.forename: Jim
authors.initials: J
authors.lastname: Barber
authors.affiliation: Johannes Kepler University Linz, Institute of Theoretical Physics, Altenberger Str. 69, AT-4040 Linz, Austria.
authors.forename: Thomas
authors.initials: T
authors.lastname: Renger
authors.affiliation: Imperial College London, South Kensington Campus, Sir Ernst Chain Building, London SW7 2AZ, UK.
authors.forename: Jasper J
authors.initials: JJ
authors.lastname: van Thor
mesh_terms: D003460:Crystallization; D007259:Infrared Rays; D008958:Models, Molecular; D045332:Photosystem II Protein Complex / Q000737:chemistry*; D046940:Synechococcus / Q000737:chemistry*
chemical_list: D045332:Photosystem II Protein Complex