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  • 51.
    Unger, Eva L.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Physical and Analytical Chemistry, Physical Chemistry.
    Morandeira, Ana
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Chemical Physics.
    Persson, Mats
    Zietz, Burkhard
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Chemical Physics.
    Ripaud, Emilie
    Leriche, Philippe
    Roncali, Jean
    Hagfeldt, Anders
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Physical and Analytical Chemistry, Physical Chemistry.
    Boschloo, Gerrit
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Physical and Analytical Chemistry, Physical Chemistry.
    Contribution from a hole-conducting dye to the photocurrent in solid-state dye-sensitized solar cells2011In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 13, no 45, p. 20172-20177Article in journal (Refereed)
    Abstract [en]

    The hole transporting medium in solid-state dye-sensitized solar cells can be utilized to harvest sunlight. Herein we demonstrate that a triphenylamine-based dye, used as hole-transporting medium, contributes to the photocurrent in a squaraine-sensitized solid-state dye-sensitized solar cell. Steady-state photoluminescence measurements have been used to distinguish between electron transfer and energy transfer processes leading to energy conversion upon light absorption in the hole-transporting dye.

  • 52.
    Viarbitskaya, Sviatlana
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Chemical Physics.
    Ryderfors, Linus
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Chemical Physics.
    Mikaelsson, Therese
    Mukhtar, Emad
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Chemical Physics.
    Johansson, Lennart B. -A.
    Luminescence Enhancement from Silica-Coated Gold Nanoparticle Agglomerates Following Multi-photon Excitation2011In: Journal of Fluorescence, ISSN 1053-0509, E-ISSN 1573-4994, Vol. 21, no 1, p. 257-264Article in journal (Refereed)
    Abstract [en]

    Multi-photon absorption induced luminescence (MAIL) from bare gold nanoparticles, silica-coated particles, as well as silica-coated agglomerated gold nanoparticles suspended in aqueous solution was studied by using time-resolved and steady-state luminescence spectroscopy. The nanoparticles were excited by femtosecond pulses of wavelengths ranging from 630 nm to 900 nm. The luminescence from the particles exhibits a broad spectrum in the UV and VIS region. The time-resolved measurements indicate a luminescence lifetime of a few ps, limited by the response of the experimental system. The studied dependence of the MAIL efficiency on the excitation wavelength showed that the luminescence from silica-coated agglomerates was enhanced over the whole range of excitation wavelengths, when compared to the luminescence from individual gold nanoparticles. The agglomerates show an almost excitation wavelength independent efficiency of the MAIL, while for individual nanoparticles a rapid decrease of the MAIL efficiency was observed with increasing excitation wavelength. The observed enhancement of the MAIL from the agglomerated nanostructures can be attributed to the presence of localized surface plasmon resonances in the spectral region corresponding to the excitation wavelengths. The high MAIL efficiency from the agglomerated nanoparticle structures in the near-infrared could be an advantage in the expanding field of luminescence-based-imaging, as well as in biosensor technology.

  • 53.
    Wallin, Staffan
    et al.
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Chemistry, Department of Physical Chemistry. Department of Biochemistry and Organic Chemistry, Organic Chemistry I. Department of Physical and Analytical Chemistry, Physical Chemistry I. Physics, Department of Physics and Materials Science, Chemical Physics.
    Davidsson, Jan
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Chemistry, Department of Physical Chemistry. Department of Biochemistry and Organic Chemistry, Organic Chemistry I. Department of Physical and Analytical Chemistry, Physical Chemistry I. Physics, Department of Physics and Materials Science, Chemical Physics.
    Modin, Judit
    Department of Chemistry. Department of Biochemistry and Organic Chemistry, Organic Chemistry I. Department of Physical and Analytical Chemistry, Physical Chemistry I. Physics, Department of Physics and Materials Science, Chemical Physics. Organisk kemi.
    Hammarström, Leif
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Chemistry, Department of Physical Chemistry. Department of Biochemistry and Organic Chemistry, Organic Chemistry I. Department of Physical and Analytical Chemistry, Physical Chemistry I. Physics, Department of Physics and Materials Science, Chemical Physics.
    Femtosecond Transient Absorption Anisotropy Study on [Ru(bpy)3]2+ and [Ru(bpy)(py)4]2+. Ultrafast Interligand Randomization of the MLCT State2005In: J. Phys. Chem. A, no 109, p. 4697-4704Article in journal (Refereed)
    Abstract [en]

    It is known that the relaxed excited state of [Ru(bpy)3]2+ is best described as a metal to ligand charge transfer (MLCT) state having one formally reduced bipyridine and two neutral. Previous reports have suggested [Malone, R. et al. J.Chem. Phys 1991, 95, 8970] that the electron "hops" from ligand to ligand in the MLCT state with a time constant of about 50 ps in acetonitrile. However, we have done transient absorption anisotropy measurements indicating that already after one picosecond the molecule has no memory of which bipyridine was initially photoselected, which suggest an ultrafast interligand randomization of the MLCT state.

  • 54.
    Wallin, Staffan
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Chemical Physics.
    Monnereau, Cyrille
    Blart, Errol
    Gankou, Jean-Richard
    Odobel, Fabrice
    Hammarström, Leif
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Chemical Physics.
    State-Selective Electron Transfer in an Unsymmetric Acceptor-Zn(II)porphyrin-Acceptor Triad: Toward a Controlled Directionality of Electron Transfer from the Porphyrin S-2 and S-1 States as a Basis for a Molecular Switch2010In: Journal of Physical Chemistry A, ISSN 1089-5639, E-ISSN 1520-5215, Vol. 114, no 4, p. 1709-1721Article in journal (Refereed)
    Abstract [en]

    A series of Zn(II) porphyrin (ZnP) compounds covalently linked to different electron acceptor units, naphthaleneimide (NI) and naphthalenedimide (NDI), are reported. The aim was to demonstrate a state-selective direction of electron transfer, where excitation to the lowest excited S-1 state of the porphyrin (Q-band excitation) would give electron transfer to the NDI unit, while excitation to the higher S-2 state (Soret-hand excitation) would give electron transfer to the NI unit. This would constitute a basis for an opto-electronic Switch in which the direction of electron transfer and the resulting dipole moment can be controlled by using light input of different color. Indeed, electron transfer from the S-1 state to NDI Occurred in solvents of both high and low polarity, whereas no electron transfer to NDI was observed from the S-2 state. With NI as acceptor instead, very rapid (tau = 200-400 fs) electron transfer from the S-2 state occurred in all solvents. This was followed by an ultrafast (tau approximate to 100 fs) recombination to Populate the porphyrin S-1 state in nearly quantitative yield. The charge-separated state ZnP+NI- was spectroscopically observed, and evidence was obtained that recombination Occurred from a vibrationally excited ("hot") ZnP+NI- state in the more polar solvents. In these solvents, the thermally relaxed ZnP+NI- state lies at lower energy than the S-1 state so that further charge separation occurred from S-1 to form ZnP+NI-. This resulted in a highly unusual "ping-pong" sequence where the reaction went back and forth between locally excited ZnP states and charge-separated states: S-2 double right arrow ZnP+NI"hot"- double right arrow S-1 double right arrow ZnP+NI- double right arrow S-0. The electron transfer dynamics and its solvent dependence are discussed, as well as the function of the present Molecules as molecular switches.

  • 55. Westenhoff, Sebastian
    et al.
    Malmerberg, Erik
    Arnlund, David
    Johansson, Linda
    Nazarenko, Elena
    Cammarata, Marco
    Davidsson, Jan
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Chemical Physics.
    Chaptal, Vincent
    Abramson, Jeff
    Katona, Gergely
    Menzel, Andreas
    Neutze, Richard
    Rapid readout detector captures protein time-resolved WAXS2010In: Nature Methods, ISSN 1548-7091, E-ISSN 1548-7105, Vol. 7, no 10, p. 775-776Article in journal (Refereed)
  • 56. Westenhoff, Sebastian
    et al.
    Nazarenko, Elena
    Malmerberg, Erik
    Davidsson, Jan
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Chemical Physics.
    Katona, Gergely
    Neutze, Richard
    Time-resolved structural studies of protein reaction dynamics: a smorgasbord of X-ray approaches2010In: Acta Crystallographica Section A: Foundations of Crystallography, ISSN 0108-7673, E-ISSN 1600-5724, Vol. 66, no 2, p. 207-219Article, review/survey (Refereed)
    Abstract [en]

    Proteins undergo conformational changes during their biological function. As such, a high-resolution structure of a protein's resting conformation provides a starting point for elucidating its reaction mechanism, but provides no direct information concerning the protein's conformational dynamics. Several X-ray methods have been developed to elucidate those conformational changes that occur during a protein's reaction, including time-resolved Laue diffraction and intermediate trapping studies on three-dimensional protein crystals, and time-resolved wide-angle X-ray scattering and X-ray absorption studies on proteins in the solution phase. This review emphasizes the scope and limitations of these complementary experimental approaches when seeking to understand protein conformational dynamics. These methods are illustrated using a limited set of examples including myoglobin and haemoglobin in complex with carbon monoxide, the simple light-driven proton pump bacteriorhodopsin, and the superoxide scavenger superoxide reductase. In conclusion, likely future developments of these methods at synchrotron X-ray sources and the potential impact of emerging X-ray free-electron laser facilities are speculated upon.

  • 57. Wohri, Annemarie B.
    et al.
    Katona, Gergely
    Johansson, Linda C.
    Fritz, Emelie
    Malmerberg, Erik
    Andersson, Magnus
    Vincent, Jonathan
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Chemical Physics.
    Eklund, Mattias
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Chemical Physics.
    Cammarata, Marco
    Wulff, Michael
    Davidsson, Jan
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Chemical Physics.
    Groenhof, Gerrit
    Neutze, Richard
    Light-Induced Structural Changes in a Photosynthetic Reaction Center Caught by Laue Diffraction2010In: Science, ISSN 0036-8075, E-ISSN 1095-9203, Vol. 328, no 5978, p. 630-633Article in journal (Refereed)
    Abstract [en]

    Photosynthetic reaction centers convert the energy content of light into a transmembrane potential difference and so provide the major pathway for energy input into the biosphere. We applied time-resolved Laue diffraction to study light-induced conformational changes in the photosynthetic reaction center complex of Blastochloris viridis. The side chain of TyrL162, which lies adjacent to the special pair of bacteriochlorophyll molecules that are photooxidized in the primary light conversion event of photosynthesis, was observed to move 1.3 angstroms closer to the special pair after photoactivation. Free energy calculations suggest that this movement results from the deprotonation of this conserved tyrosine residue and provides a mechanism for stabilizing the primary charge separation reactions of photosynthesis.

  • 58.
    Zhang, Ming-Tian
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Chemical Physics.
    Hammarström, Leif
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Chemical Physics.
    Proton-Coupled Electron Transfer from Tryptophan: A Concerted Mechanism with Water as Proton Acceptor2011In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 133, no 23, p. 8806-8809Article in journal (Refereed)
    Abstract [en]

    The mechanism of proton-coupled electron transfer (PCET) from tyrosine in enzymes and synthetic model complexes is under intense discussion, in particular the pH dependence of the PCET rate with water as proton acceptor. Here we report on the intramolecular oxidation kinetics of tryptophan derivatives linked to [Ru(bpy)(3)](2+) units with water as proton acceptor, using laser flash-quench methods. It is shown that tryptophan oxidation can proceed not only via a stepwise electron proton transfer (ETPT) mechanism that naturally shows a pH-independent rate, but also via another mechanism with a pH-dependent rate and higher kinetic isotope effect that is assigned to concerted electron-proton transfer (CEP). This is in contrast to current theoretical models, which predict that CEP from tryptophan with water as proton acceptor can never compete with ETPT because of the energetically unfavorable PT part (pK(a)(Trp(center dot)H(+)) = 4.7 >> pK(a)(H3O+) approximate to -1.5). The moderate pH dependence we observe for CEP cannot be explained by first-order reactions with OH- or the buffers and is similar to what has been demonstrated for intramolecular PCET in [Ru(bpy)(3)](3+) -tyrosine complexes (Sjodin, M.; et al. J. Am. Chem. Soc. 2000, 122, 3932. Irebo, T.; et al. J. Am. Chem. Soc. 2007, 129, 15462). Our results suggest that CEP with water as the proton acceptor proves a general feature of amino acid oxidation, and provide further experimental support for understanding of the PCET process in detail.

  • 59.
    Zhang, Ming-Tian
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Chemical Physics.
    Irebo, Tania
    Johansson, Olof
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science.
    Hammarstrom, Leif
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Chemical Physics.
    Proton-Coupled Electron Transfer from Tyrosine: A Strong Rate Dependence on Intramolecular Proton Transfer Distance2011In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 133, no 34, p. 13224-13227Article in journal (Refereed)
    Abstract [en]

    Proton-coupled electron transfer (PCET) was examined in a series of biomimetic, covalently linked Ru(II)(bpy)(3)-tyrosine complexes where the phenolic proton was H-bonded to an internal base (a benzimidazyl or pyridyl group). Photooxidation in laser flash/quench experiments generated the Ru(III) species, which triggered long-range electron transfer from the tyrosine group concerted with short-range proton transfer to the base. The results give an experimental demonstration of the strong dependence of the rate constant and kinetic isotope effect for this intramolecular PCET reaction on the effective proton transfer distance, as reflected by the experimentally determined proton donor-acceptor distance.

12 51 - 59 of 59
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