| 1. |
- Camacho Dejay, Rafael, et al.
(författare)
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Fluorescence polarization measures energy funneling in single light-harvesting antennas-LH2 vs conjugated polymers.
- 2015
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Ingår i: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322. ; 5
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Tidskriftsartikel (refereegranskat)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.
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| 2. |
- Camacho Dejay, Rafael, et al.
(författare)
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Inhomogeneous Quenching as a Limit of the Correlation Between Fluorescence Polarization and Conformation of Single Molecules
- 2013
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Ingår i: The Journal of Physical Chemistry Letters. - : American Chemical Society (ACS). - 1948-7185. ; 4:6, s. 1053-1058
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Tidskriftsartikel (refereegranskat)abstract
- The photophysical properties of conjugated polymers (CPs) largely depend on the interactions between the CP and its environment. We present a study of two polymers with identical conjugated backbones, bare and insulated, that showed different fluorescence excitation modulation depth histograms. However, the polarization differences are not related to differences in conformation, as commonly believed, but to the existence of "dark" chromophores in the bare polymer that are statically quenched. This results in inhomogeneous quenching of the polymer chain that breaks the correlation between excitation fluorescence polarization and conjugated polymer chain conformation.
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| 3. |
- Camacho Dejay, Rafael, et al.
(författare)
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Polarization Imaging of Emissive Charge Transfer States in Polymer/Fullerene Blends
- 2014
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Ingår i: Chemistry of Materials. - : American Chemical Society (ACS). - 0897-4756 .- 1520-5002. ; 26:23, s. 6695-6704
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Tidskriftsartikel (refereegranskat)abstract
- Photoexcitation of conjugated polymerfullerene blends results in population of a local charge transfer (CT) state at the interface between the two materials. The competition between recombination and dissociation of this interfacial state limits the generation of fully separated free charges. Therefore, a detailed understanding of the CT states is critical for building a comprehensive picture of the organic solar cells operation. We applied a new fluorescence microscopy method called two-dimensional polarization imaging to gain insight into the orientation of the transition dipole moments of the CT states, and the associated excitation energy transfer processes in TQ1:PCBM blend films. The polymer phase was oriented mechanically to relate the polymer dipole moment orientation to that of the CT states. CT state formation was observed to be much faster than energy transfer in the polymer phase. However, after being formed an emissive CT state does not exchange excitation energy with other CT states, suggesting that they are spatially and/or energetically isolated. We found that the quantum yield of the CT emission is smaller for CT states spatially located in the highly oriented polymer domains, which is interpreted as the result of enhanced CT state dissociation in highly ordered structures.
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| 4. |
- Camacho Dejay, Rafael
(författare)
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Polarization portraits of lightharvesting antennas: from single molecule spectroscopy to imaging
- 2014
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Multichromophoric systems are very important in photosynthesis and any device that uses solar energy for its operation. This is because multichromophoric light-harvesting antennas are responsible for the absorption of light and the efficient transfer of the absorbed energy toward distinct places where it is to be used or stored. Over the last 10 years polarization sensitive single molecule methods have been extensively used to study the chromophore organisation and excitation energy transfer processes in lightharvesting antennas. In general, these methods probe in separate experiments the fluorescence excitation and emission polarization properties of the sample. This approach unfortunately averages out meaningful correlations between the polarization properties of the chromophores preferentially absorbing light, and the polarization state of the emitted fluorescence. Therefore, in 2009 an alternative method was proposed to detect these correlations called two dimensional polarization imaging. This is done by measuring a two dimensional function that describes the fluorescence intensity and polarization of a single object as a function of the electric field´s direction of the linearly polarized excitation light. However, in spite of the development of the technique, the main challenge still was to extract the excitation energy transfer information from the data. In this thesis we report the further understanding of the theoretical and experimental challenges developed for two dimension polarization imaging. Our development made possible the quantitative characterization of the excitation energy transfer efficiency of individual light-harvesting antennas, such as the LH2 complex and conjugated polymers, through a model based on a single funnel approximation. This method can be used to assess the “quality” of an artificial light harvesting antenna before trying it in a device. Further, we showed that our methodology is not only beneficial for studying of single molecules, but also can be used as a fluorescence imaging microscopy where parameters related to energy transfer and the chromophore organisation serve as imaging contrast. Two dimensional polarization imaging in combination with the single funnel approximation was successfully used to study thin films of a solar cell material, and is being tested on cell cultures and histological samples. The energy transfer sensitivity of our imaging technique opens exciting applications in life sciences for the study of biologically relevant systems, such as the aggregation of proteins involved in the causes of various diseases.
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| 5. |
- Camacho Dejay, Rafael, et al.
(författare)
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Quantitative characterization of light-harvesting efficiency in single molecules and nanoparticles by 2D polarization microscopy: Experimental and theoretical challenges
- 2012
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Ingår i: Chemical Physics. - : Elsevier BV. - 0301-0104. ; 406, s. 30-40
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Tidskriftsartikel (refereegranskat)abstract
- General problem of extracting intramolecular energy transfer information from fluorescence and fluorescence excitation polarization experiments at single molecule level is presented. A single funnel approximation is shown to be a very powerful approach to model the polarization data obtained by recently emerged 2-dimensional polarization single molecule imaging technique [O. Mirzov et al., Small 5 (2009) 1877]. Using this approximation a parameter characterising quantitatively light-harvesting efficiency of an individual light-harvesting antenna can be readily obtained. Technical details of 2D polarization imaging and practical methods of avoiding polarization artefact in fluorescence microscopy are discussed. (C) 2012 Elsevier B. V. All rights reserved.
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| 6. |
- Lin, Hongzhen, et al.
(författare)
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Collective Fluorescence Blinking in Linear J-Aggregates Assisted by Long-Distance Exciton Migration.
- 2010
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Ingår i: Nano Letters. - : American Chemical Society (ACS). - 1530-6992 .- 1530-6984. ; 10:2, s. 620-626
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Tidskriftsartikel (refereegranskat)abstract
- Fluorescence blinking corresponding to collective quenching of up to 100 dye monomers is reported for individual J-aggregates of a perylene bisimide (PBI) dye. This implies an exciton diffusion length up to 70 nm in these one-dimensional assemblies. The number of quenched monomers was directly measured by comparing the fluorescence brightness of the J-aggregates with that of noncoupled PBI molecules. This brightness analysis technique is useful for unraveling photophysical parameters of any individual fluorescent nanosystem.
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| 7. |
- Merdasa, Aboma, et al.
(författare)
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Single Levy States-Disorder Induced Energy Funnels in Molecular Aggregates
- 2014
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Ingår i: Nano Letters. - : American Chemical Society (ACS). - 1530-6992 .- 1530-6984. ; 14:12, s. 6774-6781
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Tidskriftsartikel (refereegranskat)abstract
- Using fluorescence super-resolution microscopy we studied simultaneous spectral, spatial localization, and blinking behavior of individual 1D J-aggregates. Excitons migrating 100 nm are funneled to a trap appearing as an additional red-shifted blinking fluorescence band. We propose that the trap is a Frenkel exciton state formed much below the main exciton band edge due to an environmentally induced heavy-tailed Levy disorder. This points to disorder engineering as a new avenue in controlling light-harvesting in molecular ensembles.
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| 8. |
- Siebert, Ronald, et al.
(författare)
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Fluorescence quenching in Zn2+-bis-terpyridine coordination polymers: a single molecule study
- 2012
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Ingår i: Journal of Materials Chemistry. - : Royal Society of Chemistry (RSC). - 1364-5501 .- 0959-9428. ; 22:31, s. 16041-16050
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Tidskriftsartikel (refereegranskat)abstract
- A Zn2+-bis-terpyridine coordination polymer is investigated by single-molecule fluorescence spectroscopy (SMS). The bis-terpyridine ligands of the coordination polymers bear conjugated chromophores connecting the terpyridine spheres of the ligands, which resemble structural features of MEH-PPV. To the best of our knowledge this paper presents the first systematic SMS study on Zn2+-bis-terpyridine coordination polymers. Upon incorporation of free chromophores into the polymer, the fluorescence quantum yield of individual chromophores appears to be reduced. The reason for the reduced emission per chromophore in a polymer is investigated by brightness studies on single isolated polymer molecules. Furthermore, the experiments reveal that the Zn2+-bis-terpyridine coordination polymer contains a significantly larger fraction of effective chromophores, compared to one of the most common conjugated polymers, e. g., MEH-PPV. This finding is attributed to the particularly rigid geometry of the system at hand, which was corroborated by polarization-dependent experiments. Time-resolved experiments identified two different types of intensity fluctuations: small amplitude intensity fluctuations might correlate with switching of individual chromophores by structural fluctuations, while large amplitude jumps switch off the emission of the entire molecule. Finally, experiments under different atmospheric conditions offer further insights into the molecular mechanism and the nature of the quenchers involved in the blinking.
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| 9. |
- Thomsson, Daniel, et al.
(författare)
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Cyclodextrin Insulation Prevents Static Quenching of Conjugated Polymer Fluorescence at the Single Molecule Level.
- 2013
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Ingår i: Small. - : Wiley. - 1613-6829 .- 1613-6810. ; 9:15, s. 2619-2627
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Tidskriftsartikel (refereegranskat)abstract
- Conjugated polymers (CPs) are promising materials for fluorescence imaging application. However, a significant problem in this field is the unexplained abnormally low fluorescence brightness (or number of fluorescence photons detected per one excitation photon) exhibited by most of CP single chains in solid polymer hosts. Here it is shown that this detrimental effect can be fully avoided for short chains of polyfluorene-bis-vinylphenylene (PFBV) embedded in a host polymer matrix of PMMA, if the conjugated backbone is insulated by cyclodextrin rings to form a polyrotaxane (PFBV-Rtx). Fluorescence kinetics and quantum yields are measured for the polymers in liquid solutions, pristine films, and solid PMMA blends. The fluorescence brightness of PFBV-Rtx single chains dispersed in a solid PMMA is very close to that expected for a chain with 100% fluorescence quantum yield, while the unprotected PFBV chains of the same length possess 4 times lower brightness. Despite this, the fluorescence decay kinetics are the same for both polymers, suggesting the presence of static or ultrafast fluorescence quenching in the unprotected polymer. About 80% of an unprotected PFBV chain is estimated to be completely quenched. The hypothesis is that the cyclodextrin rings prevent the quenching by working as 'bumpers' reducing the mechanical forces applied by the host polymer to the conjugated backbone and help retaining its conformational freedom. While providing a recipe for making CP fluorescence bright at the single-molecule level, these results identify a lack of fundamental understanding in the community of the influence of the environment on excited states in conjugated materials.
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| 10. |
- Tian, Yuxi, et al.
(författare)
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Organization of Bacteriochlorophylls in Individual Chlorosomes from Chlorobaculum tepidum Studied by 2-Dimensional Polarization Fluorescence Microscopy
- 2011
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Ingår i: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 1520-5126 .- 0002-7863. ; 133:43, s. 17192-17199
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Tidskriftsartikel (refereegranskat)abstract
- Chlorosomes are the largest and most efficient natural light-harvesting systems and contain supramolecular assemblies of bacteriochlorophylls that are organized without proteins. Despite a recent structure determination for chlorosomes from Chlorobaculum tepidum (Ganapathy et al. Proc. Natl. Acad. Sci. U.S.A. 2009, 106, 8525), the issue of a possible large structural disorder is still discussed controversially. We have studied individual chlorosomes prepared under very carefully controlled growth condition by a novel 2-dimensional polarization single molecule imaging technique giving polarization information for both fluorescence excitation and emission simultaneously. Contrary to the existing literature data, the polarization degree or modulation depth (M) for both excitation (absorption) and emission (fluorescence) showed extremely narrow distributions. The fluorescence was always highly polarized with M approximate to 0.77, independent of the excitation wavelength. Moreover, the fluorescence spectra of individual chlorosomes were identical within the error limits. These results lead us to conclude that all chlorosomes possess the same type of internal organization in terms of the arrangement of the bacteriochlorophyll c transition dipole moments and their total excitonic transition dipole possess a cylindrical symmetry in agreement with the previously suggested concentric multitubular chlorophyll aggregate organization (Ganapathy et al. Proc. Natl. Acad. Sci. U.S.A. 2009, 106, 8525).
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