title: Fluorescence polarization measures energy funneling in single light-harvesting antennas--LH2 vs conjugated polymers.
abstract: Numerous approaches have been proposed to mimic natural photosynthesis using artificial antenna systems, such as conjugated polymers (CPs), dendrimers, and J-aggregates. As a result, there is a need to characterize and compare the excitation energy transfer (EET) properties of various natural and artificial antennas. Here we experimentally show that EET in single antennas can be characterized by 2D polarization imaging using the single funnel approximation. This methodology addresses the ability of an individual antenna to transfer its absorbed energy towards a single pool of emissive states, using a single parameter called energy funneling efficiency (ε). We studied individual peripheral antennas of purple bacteria (LH2) and single CP chains of 20 nm length. As expected from a perfect antenna, LH2s showed funneling efficiencies close to unity. In contrast, CPs showed lower average funneling efficiencies, greatly varying from molecule to molecule. Cyclodextrin insulation of the conjugated backbone improves EET, increasing the fraction of CPs possessing ε = 1. Comparison between LH2s and CPs shows the importance of the protection systems and the protein scaffold of LH2, which keep the chromophores in functional form and at such geometrical arrangement that ensures excellent EET.
authors.affiliation: Chemical Physics, Lund University, PO Box 124, Lund, SE-22100, Sweden.
authors.forename: Rafael
authors.initials: R
authors.lastname: Camacho
authors.affiliation: Chemical Physics, Lund University, PO Box 124, Lund, SE-22100, Sweden.
authors.forename: Sumera
authors.initials: S
authors.lastname: Tubasum
authors.affiliation: Glasgow Biomedical Research Centre, University of Glasgow, G12 8QQ, United Kingdom.
authors.forename: June
authors.initials: J
authors.lastname: Southall
authors.affiliation: Glasgow Biomedical Research Centre, University of Glasgow, G12 8QQ, United Kingdom.
authors.forename: Richard J
authors.initials: RJ
authors.lastname: Cogdell
authors.affiliation: Department of Chemistry, University of Oxford, Mansfield Road, Oxford, OX1 3TA, United Kingdom.
authors.forename: Giuseppe
authors.initials: G
authors.lastname: Sforazzini
authors.affiliation: Department of Chemistry, University of Oxford, Mansfield Road, Oxford, OX1 3TA, United Kingdom.
authors.forename: Harry L
authors.initials: HL
authors.lastname: Anderson
authors.affiliation: Chemical Physics, Lund University, PO Box 124, Lund, SE-22100, Sweden.
authors.forename: Tõnu
authors.initials: T
authors.lastname: Pullerits
authors.affiliation: Chemical Physics, Lund University, PO Box 124, Lund, SE-22100, Sweden.
authors.forename: Ivan G
authors.initials: IG
authors.lastname: Scheblykin
mesh_terms: D000465:Algorithms; D004735:Energy Transfer; D005454:Fluorescence Polarization; D008027:Light; D008962:Models, Theoretical; D010788:Photosynthesis; D011108:Polymers
chemical_list: D011108:Polymers