| 1. |
- Aissaoui, Nesrine, 1983, et al.
(författare)
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FRET enhancement close to gold nanoparticles positioned in DNA origami constructs
- 2017
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Ingår i: Nanoscale. - Cambridge, United Kingdom : Royal Society of Chemistry (RSC). - 2040-3372 .- 2040-3364. ; 9:2, s. 673-683
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Tidskriftsartikel (refereegranskat)abstract
- Here we investigate the energy transfer rates of a Förster resonance energy transfer (FRET) pair positioned in close proximity to a 5 nm gold nanoparticle (AuNP) on a DNA origami construct. We study the distance dependence of the FRET rate by varying the location of the donor molecule, D, relative to the AuNP while maintaining a fixed location of the acceptor molecule, A. The presence of the AuNP induces an alteration in the spontaneous emission of the donor (including radiative and non-radiative rates) which is strongly dependent on the distance between the donor and AuNP surface. Simultaneously, the energy transfer rates are enhanced at shorter D-A (and D-AuNP) distances. Overall, in addition to the direct influence of the acceptor and AuNP on the donor decay there is also a significant increase in decay rate not explained by the sum of the two interactions. This leads to enhanced energy transfer between donor and acceptor in the presence of a 5 nm AuNP. We also demonstrate that the transfer rate in the three "particle" geometry (D + A + AuNP) depends approximately linearly on the transfer rate in the donor-AuNP system, suggesting the possibility to control FRET process with electric field induced by 5 nm AuNPs close to the donor fluorophore. It is concluded that DNA origami is a very versatile platform for studying interactions between molecules and plasmonic nanoparticles in general and FRET enhancement in particular.
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| 2. |
- Albinsson, Bo, 1963, et al.
(författare)
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Polarized Spectroscopy with Fluorescent Biomolecular Building Blocks
- 2016
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Ingår i: Fluorescent Analogues of Biomolecular Building Blocks: Design and Applications: Design and Applications (eds M. Wilhelmsson and Y. Tor). - Hoboken, NJ, USA : John Wiley & Sons, Inc. - 9781118175866 ; , s. 40-54
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Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- © 2016 by John Wiley & Sons, Inc. All rights reserved. This chapter considers linear dichroism (LD), magnetic circular dichroism (MCD), and Forster resonance energy transfer (FRET) and how these phenomena are related to and may report on transition moment orientations and on molecular structure. MCD is an asset in combination with LD and fluorescence anisotropy for the deciphering of transition moment directions in biophysically important chromophores, and many examples of applications are found among nucleobases. A property corresponding to the absorption anisotropy (linear dichroism) for emission is the fluorescence anisotropy. The amino acid tryptophan, with indole as its photoactive aromatic chromophore, is the most frequently used natural fluorescent probe in biophysical contexts, due to its relatively high fluorescence quantum yield and well-resolved absorption profile in the near-UV. The single-molecule fluorescence-detected linear dichroism (smFLD) method is a useful complement to smFRET since it can help to avoid misinterpretation of false smFRET signals.
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| 3. |
- Dzebo, Damir, 1986, et al.
(författare)
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Intramolecular Triplet-Triplet Annihilation Upconversion in 9,10-Diphenylanthracene Oligomers and Dendrimers
- 2016
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Ingår i: Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 120:41, s. 23397-23406
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Tidskriftsartikel (refereegranskat)abstract
- An important challenge when developing materials for triplet triplet annihilation upconversion (TTA-UC) is achieving efficient and well-functioning solid-state systems. We here explore the effect of intramolecular TTA in oligomers and dendrimers based on the 9,10-diphenylanthracene (DPA) chromophore. The macromolecules are sensitized using palladium porphyrin, both in solution and in solid poly(methyl methacrylate) (PMMA), demonstrating a positive effect on overall upconversion in the solid state correlating with the well-controlled size of the DPA constructs. The UC kinetics is modeled and fit to steady-state and time-resolved emission data to give further insight into the intramolecular excited-state migration and annihilation in the macromolecular annihilator systems.
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| 4. |
- Dzebo, Damir, 1986, et al.
(författare)
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Robust triplet-triplet annihilation photon upconversion by efficient oxygen scavenging
- 2017
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Ingår i: Photochemical and Photobiological Sciences. - : Springer Science and Business Media LLC. - 1474-9092 .- 1474-905X. ; 16:8, s. 1327-1334
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Tidskriftsartikel (refereegranskat)abstract
- We hereby present a simple method for reducing the effect of oxygen quenching in Triplet-Triplet Annihilation Upconversion (TTA-UC) systems. A number of commercially available thioethers and one thiol have been tested as singlet oxygen scavengers. Recording of the upconverted emission from a well-studied PdOEP (sensitizer)-DPA (annihilator/emitter) couple has been made over time with steady-state excitation capturing the steady-state kinetics of the TTA-UC process as the solubilized oxygen is depleted by reaction with the scavengers. The efficiency of the TTA-UC process is compared between chemical oxygen scavenging and mechanical removal by inert gas purging or the freeze-pump-thaw method. Selected methods are combined to explore the highest attainable TTA-UC quantum yield. A maximum TTA-UC quantum yield of 21% with the shortest UC onset time was obtained with dimethylthiomethane (DMTM) as the scavenger in an air-saturated solvent and slightly higher quantum yields were obtained in combination with other deoxygenation techniques. Samples containing DMTM displayed little decrease in the quantum yield over four hours of continuous high intensity irradiation, which illustrates the robustness of applying chemical oxygen removal in TTA-UC instead of more time-consuming mechanical processes that usually require specialized equipment.
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| 5. |
- Edhborg, Fredrik, 1990, et al.
(författare)
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Singlet Energy Transfer in Anthracene-Porphyrin Complexes: Mechanism, Geometry, and Implications for Intramolecular Photon Upconversion
- 2019
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Ingår i: Journal of Physical Chemistry B. - : American Chemical Society (ACS). - 1520-5207 .- 1520-6106. ; 123:46, s. 9934-9943
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Tidskriftsartikel (refereegranskat)abstract
- In this work we show that the mechanism for singlet excitation energy transfer (SET) in coordination complexes changes upon changing a single atom. SET is governed by two different mechanisms; Förster resonance energy transfer (FRET) based on Coulombic, through-space interactions, or Dexter energy transfer relying on exchange, through-bond interactions. On the basis of time-resolved fluorescence and transient absorption measurements, we conduct a mechanistic study of SET from a set of photoexcited anthracene donors to axially coordinated porphyrin acceptors, revealing the effect of coordination geometry and a very profound effect of the porphyrin central metal atom. We found that FRET is the dominating mechanism of SET for complexes with zinc-octaethylporphyrin (ZnOEP) as the acceptor, while Dexter energy transfer is the dominating mechanism of SET in a corresponding ruthenium complex (RuOEP). In addition, by analyzing the coordination geometry of the complexes and its temperature dependence, the binding angle potential energy of axially coordinated porphyrin complexes could be estimated. The results of this study are of fundamental importance and are discussed with respect to the consequences for developing intramolecular triplet-Triplet annihilation photon upconversion in coordination complexes.
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| 6. |
- Gilbert Gatty, Melina, 1986, et al.
(författare)
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Hopping versus Tunneling Mechanism for Long-Range Electron Transfer in Porphyrin Oligomer Bridged Donor-Acceptor Systems
- 2015
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Ingår i: Journal of Physical Chemistry B. - : American Chemical Society (ACS). - 1520-5207 .- 1520-6106. ; 119:24, s. 7598-7611
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Tidskriftsartikel (refereegranskat)abstract
- Achieving long-range charge transport in molecular systems is interesting to foresee applications of molecules in practical devices. However, designing molecular systems with pre-defined wire-like properties remains difficult due to the lack of understanding of the mechanism for charge transfer. Here we investigate a series of porphyrin oligomer-bridged donor–acceptor systems Fc–Pn–C60 (n = 1–4, 6). In these triads, excitation of the porphyrin-based bridge generates the fully charge-separated state, Fc•+–Pn–C60•-, through a sequence of electron transfer steps. Temperature dependence of both charge separation (Fc–Pn*–C60 → Fc–Pn•+–C60•-) and recombination (Fc•+–Pn–C60•– → Fc–Pn–C60) processes was probed by time-resolved fluorescence and femtosecond transient absorption. In the long triads, two mechanisms contribute to recombination of Fc•+–Pn–C60•– to the ground state. At high temperatures (≥280 K), recombination via tunneling dominates for the entire series. At low temperatures (
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| 7. |
- Gilbert Gatty, Melina, 1986, et al.
(författare)
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Photoinduced charge and energy transfer in molecular wires
- 2015
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Ingår i: Chemical Society Reviews. - : Royal Society of Chemistry (RSC). - 1460-4744 .- 0306-0012. ; 44:4, s. 845-862
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Forskningsöversikt (refereegranskat)abstract
- Exploring charge and energy transport in donor-bridge-acceptor systems is an important research field which is essential for the fundamental knowledge necessary to develop future applications. These studies help creating valuable knowledge to respond to today's challenges to develop functionalized molecular systems for artificial photosynthesis, photovoltaics or molecular scale electronics. This tutorial review focuses on photo-induced charge/energy transfer in covalently linked donor-bridge-acceptor (D-B-A) systems. Of utmost importance in such systems is to understand how to control signal transmission, i.e. how fast electrons or excitation energy could be transferred between the donor and acceptor and the role played by the bridge (the "molecular wire"). After a brief description of the electron and energy transfer theory, we aim to give a simple yet accurate picture of the complex role played by the bridge to sustain donor-acceptor electronic communication. Special emphasis is put on understanding bridge energetics and conformational dynamics effects on the distance dependence of the donor-acceptor electronic coupling and transfer rates. Several examples of donor-bridge-acceptor systems from the literature are described as a support to the discussion. Finally, porphyrin-based molecular wires are introduced, and the relationship between their electronic structure and photophysical properties is outlined. In strongly conjugated porphyrin systems, limitations of the existing electron transfer theory to interpret the distance dependence of the transfer rates are also discussed.
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| 8. |
- Gray, Victor, 1988, et al.
(författare)
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Loss channels in triplet-triplet annihilation photon upconversion: importance of annihilator singlet and triplet surface shapes
- 2017
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Ingår i: Physical Chemistry Chemical Physics. - : Royal Society of Chemistry (RSC). - 1463-9084 .- 1463-9076. ; 19:17, s. 10931-10939
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Tidskriftsartikel (refereegranskat)abstract
- Triplet-triplet annihilation photon upconversion (TTA-UC) can, through a number of energy transfer processes, efficiently combine two low frequency photons into one photon of higher frequency. TTA-UC systems consist of one absorbing species (the sensitizer) and one emitting species (the annihilator). Herein, we show that the structurally similar annihilators, 9,10-diphenylanthracene (DPA, 1), 9-(4-phenylethynyl)10-phenylanthracene (2) and 9,10-bis(phenylethynyl) anthracene (BPEA, 3) have very different upconversion efficiencies, 15.2 +/- 2.8%, 15.9 +/- 1.3% and 1.6 +/- 0.8%, respectively (of a maximum of 50%). We show that these results can be understood in terms of a loss channel, previously unaccounted for, originating from the difference between the BPEA singlet and triplet surface shapes. The difference between the two surfaces results in a fraction of the triplet state population having geometries not energetically capable of forming the first singlet excited state. This is supported by TD-DFT calculations of the annihilator excited state surfaces as a function of phenyl group rotation. We thereby highlight that the commonly used "spin-statistical factor'' should be used with caution when explaining TTA-efficiencies. Furthermore, we show that the precious metal free zinc octaethylporphyrin (ZnOEP) can be used for efficient sensitization and that the upconversion quantum yield is maximized when sensitizer-annihilator spectral overlap is minimized (ZnOEP with 2).
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| 9. |
- Gray, Victor, 1988, et al.
(författare)
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Photophysical characterization of the 9,10-disubstituted anthracene chromophore and its applications in triplet-triplet annihilation photon upconversion
- 2015
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Ingår i: Journal of Materials Chemistry C. - : Royal Society of Chemistry (RSC). - 2050-7526 .- 2050-7534. ; 3:42, s. 11111-11121
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Tidskriftsartikel (refereegranskat)abstract
- Molecules based on anthracene are commonly used in applications such as OLEDs and triplet-triplet annihilation upconversion. In future design of blue emitting materials it is useful to know which part of the molecule can be altered in order to obtain new physical properties without losing the inherent optical properties. We have studied the effect of substitution of 9,10-substituted anthracenes. Eight anthracenes with aromatic phenyl and thiophene substituents were synthesised, containing both electron donating and accepting groups. The substitutions were found to affect the UV/Vis absorption only to a small extent, however the fluorescence properties were more affected with the thiophene substituents that decreased the fluorescence quantum yield from unity to
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| 10. |
- Gray, Victor, 1988, et al.
(författare)
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Porphyrin-Anthracene Complexes: Potential in Triplet-Triplet Annihilation Upconversion
- 2016
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Ingår i: Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 120:34, s. 19018-19026
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Tidskriftsartikel (refereegranskat)abstract
- Triplet-triplet annihilation photon upconversion (TTA-UC) systems contain both an absorbing and an emitting molecule, the sensitizer and annihilator, respectively. Through a series of energy-transfer steps, two low frequency,photons can be combined into one high frequency photon. In organic solvents, the required energy transfer steps are limited by diffusion and are relatively efficient. In solid-state systems, however, the diffusion is slower, which usually results in lower efficiencies for these systems. An interesting way around this is to connect the sensitizer and annihilator. In order to increase understanding of the TTA-UC process in supramolecular systems, we synthesized four pyridine-substituted anthracene annihilators capable of coordinating axially to a zinc octaethylporphyrin sensitizer with a maximum binding constant of 6000 M-1 in toluene. This is a first example of a sensitizer-annihilator coordination complex for TTA-UC. Both the upconversion efficiency and the parasitic quenching of excited annihilator singlets by the sensitizer through Forster resonant energy transfer (FRET) were studied. On the basis of the findings herein, possible strategies for future supramolecular TTA systems with minimized FRET quenching are discussed.
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