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  • 1.
    Abrahamsson, Maria
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Chemical Physics.
    Becker, Hans-Christian
    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.
    Bonnefous, Celine
    Chamchoumis, Charles
    Thummel, Randolph
    Six-membered Ring Chelate Complexes of Ru(II): Structural and photophysical effects2007In: Inorganic Chemistry, ISSN 0020-1669, E-ISSN 1520-510X, Vol. 46, no 24, p. 10354-10364Article in journal (Refereed)
    Abstract [en]

    The structural and photophysical properties of Ru(II)−polypyridyl complexes with five- and six-membered chelate rings were studied for two bis-tridentate and two tris-bidentate complexes. The photophysical effect of introducing a six-membered chelate ring is most pronounced for the tridentate complex, leading to a room-temperature excited-state lifetime of 810 ns, a substantial increase from 180 ns for the five-membered chelate ring model complex. Contrasting this, the effect is the opposite in tris-bidentate complexes, in which the lifetime decreases from 430 ns to around 1 ns in going from a five-membered to six-membered chelate ring. All of the complexes were studied spectroscopically at both 80 K and ambient temperatures, and the temperature dependence of the excited-state lifetime was investigated for both of the bis-tridentate complexes. The main reason for the long excited-state lifetime in the six-membered chelate ring bis-tridentate complex was found to be a strong retardation of the activated decay via metal-centered states, largely due to an increased ligand field splitting due to the complex having a more-octahedral geometry.

  • 2.
    Abrahamsson, Maria
    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.
    Tocher, Derek
    Nag, Samik
    Datta, Dipankar
    Modulation of the lowest metal-to-ligand charge-transfer state in [Ru(bpy)(2)(N-N)](2+) systems by changing the N-N from hydrazone to azine: Photophysical Consequences2006In: Inorganic Chemistry, ISSN 0020-1669, E-ISSN 1520-510X, Vol. 45, no 23, p. 9580-9586Article in journal (Refereed)
    Abstract [en]

    Two Ru( II) complexes, [ Ru( bpy) L-2]( ClO4) 2 ( 1) and [ Ru( bpy)(2)L']( BF4) 2 ( 2), where bpy is 2,2'-bipyridine, L is diacetyl dihydrazone, and L' 1: 2 is the condensate of L and acetone, are synthesized. From X-ray crystal structures, both are found to contain distorted octahedral RuN62+ cores. NMR spectra show that the cations in 1 and 2 possess a C-2 axis in solution. They display the expected metal-to-ligand charge transfer ( (MLCT)-M-1) band in the 400 - 500 nm region. Complex 1 is nonemissive at room temperature in solution as well as at 80 K. In contrast, complex 2 gives rise to an appreciable emission upon excitation at 440 nm. The room-temperature emission is centered at 730 nm ( lambda(max)(em)) with a quantum yield ( em) of 0.002 and a lifetime ( tau(em)) of 42 ns in an air-equilibrated methanol - ethanol solution. At 80 K, Phi(em) = 0.007 and tau(em)= 178 ns, with a lambda(max)(em) of 690 nm, which is close to the 0 - 0 transition, indicating an (MLCT)-M-3 excited-state energy of 1.80 eV. The radiative rate constant ( 5 x 10(4) s(-1)) at room temperature and 80 K is almost temperature independent. From spectroelectrochemistry, it is found that bpy is easiest to reduce in 2 and that L is easiest in 1. The implications of this are that in 2 the lowest (MLCT)-M-3 state is localized on a bpy ligand and in 1 it is localized on L. Transient absorption results also support these assignments. As a consequence, even though 2 shows a fairly strong and long-lived emission from a Ru( II) -> bpy CT state, the Ru( II) -> L CT state in 1 shows no detectable emission even at 80 K.

  • 3.
    Beyler, Maryline
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science.
    Ezzaher, Salah
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science.
    Karnahl, Michael
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Molecular Biomimetics.
    Santoni, Marie-Pierre
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Molecular Biomimetics.
    Lomoth, Reiner
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Chemical Physics.
    Ott, Sascha
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Molecular Biomimetics.
    Pentacoordinate iron complexes as functional models of the distal iron in [FeFe] hydrogenases2011In: Chemical Communications, ISSN 1359-7345, E-ISSN 1364-548X, Vol. 47, no 42, p. 11662-11664Article in journal (Refereed)
    Abstract [en]

    Mononuclear pentacoordinate iron complexes with a free coordination site were prepared as mimics of the distal Fe (Fe(d)) in the active site of [FeFe] hydrogenases. The complexes catalyze the electrochemical reduction of protons at mild overpotential.

  • 4. Boixel, Julien
    et al.
    Fortage, Jerome
    Blart, Errol
    Pellegrin, Yann
    Hammarström, Leif
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Chemical Physics.
    Becker, Hans-Christian
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Chemical Physics.
    Odobel, Fabrice
    Extension of the charge separated-state lifetime by supramolecular association of a tetrathiafulvalene electron donor to a zinc/gold bisporphyrin2010In: Dalton Transactions, ISSN 1477-9226, E-ISSN 1477-9234, Vol. 39, no 6, p. 1450-1452Article in journal (Refereed)
    Abstract [en]

    Supramolecular triads were prepared by self-assembly of 4'-pyridyl-2-tetrathiafulvalene axially bound on ZnP-spacer-AuP+ dyads; the lifetime of the charge separated state (+TTF-ZnP-Spacer-AuP center dot) formed upon light excitation of the triad is greatly increased with respect to that found in the parent dyad.

  • 5.
    Borg, O Anders
    et al.
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Quantum Chemistry. Chemistry, Department of Physical and Analytical Chemistry, Quantum Chemistry. Department of Physics and Materials Science, Chemical Physics. Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Chemistry, Department of Physical and Analytical Chemistry. Avdelningen för kvantkemi.
    Liu, Ya-Jun
    Persson, Petter
    Lunell, Sten
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Quantum Chemistry. Chemistry, Department of Physical and Analytical Chemistry, Quantum Chemistry. Department of Physics and Materials Science, Chemical Physics. Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Chemistry, Department of Physical and Analytical Chemistry. Avdelningen för kvantkemi.
    Karlsson, Daniel
    Department of Photochemistry and Molecular Science. Chemistry, Department of Physical and Analytical Chemistry, Quantum Chemistry. Department of Physics and Materials Science, Chemical Physics.
    Kadi, Malin
    Davidsson, Jan
    Department of Photochemistry and Molecular Science. Chemistry, Department of Physical and Analytical Chemistry, Quantum Chemistry. Department of Physics and Materials Science, Chemical Physics.
    Photochemistry of bromofluorobenzenes.2006In: J Phys Chem A Mol Spectrosc Kinet Environ Gen Theory, ISSN 1089-5639, Vol. 110, no 22, p. 7045-56Article in journal (Refereed)
  • 6.
    Cappel, Ute B.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Physical and Analytical Chemistry, Physical Chemistry.
    Smeigh, Amanda L.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Chemical Physics.
    Plogmaker, Stefan
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Surface and Interface Science.
    Johansson, Erik M. J.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Physical and Analytical Chemistry, Physical Chemistry.
    Rensmo, Håkan
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Surface and Interface Science.
    Hammarström, Leif
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Chemical Physics.
    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.
    Characterization of the Interface Properties and Processes in Solid State Dye-Sensitized Solar Cells Employing a Perylene Sensitizer2011In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 115, no 10, p. 4345-4358Article in journal (Refereed)
    Abstract [en]

    We recently reported on a perylene sensitizer, ID176, which performs much better in solid state dye-sensitized solar cells than in those using liquid electrolytes with iodide/tri-iodide as the redox couple (J. Phys. Chem. C2009, 113, 14595-14597). Here, we present a characterization of the sensitizer and of the TiO2/dye interface by UV-visible absorption and fluorescence spectroscopy, spectroelectrochemistry, photoelectron spectroscopy, electroabsorption spectroscopy, photoinduced absorption spectroscopy, and femtosecond transient absorption measurements. We report that the absorption spectrum of the sensitizer is red-shifted by addition of lithium ions to the surface due to a downward shift of the excited state level of the sensitizer, which is of the same order of magnitude as the downward shift of the titanium dioxide conduction band edge. Results from photoelectron spectroscopy and electrochemistry suggest that the excited state is largely located below the conduction band edge of TiO2 but that there are states in the band gap of TiO2 which might be available for photoinduced electron injection. The sensitizer was able to efficiently inject into TiO2, when a lithium salt was present on the surface, while injection was much less effective in the absence of lithium ions or in the presence of solvent. In the presence of the hole conductor 2,2-,7,7-tetrakis-(N,N-di-p-methoxyphenyl-amine)-9,9-spirobifluorene (spiro-MeOTAD) and LiTFSI, charge separation was monitored by the emergence of a Stark shift of the dye in transient absorption spectra, and both injection and regeneration appear to be completed within 1 ps. Regeneration by spiro-MeOTAD is therefore several orders of magnitude faster than regeneration by iodide, and ID176 can even be photoreduced by spiro-MeOTAD.

  • 7. Chaignon, Frederique
    et al.
    Blart, Errol
    Borgström, Magnus
    Hammarström, Leif
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Chemistry, Department of Photochemistry and Molecular Science. Physics, Department of Physics and Materials Science, Chemical Physics.
    Odobel, Fabrice
    Design of molecular architectures to mimic photosynthesis2006In: Actualite Chimique, Vol. 297, p. 23-27Article in journal (Refereed)
  • 8. Chaignon, Frederique
    et al.
    Falkenström, Magnus
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Chemical Physics.
    Karlsson, Susanne
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Chemical Physics.
    Blart, Errol
    Odobel, Fabrice
    Hammarström, Leif
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Chemical Physics.
    Very large acceleration of the photoinduced electron transfer in a Ru(bpy) 3-naphthalene bisimide dyad bridged on the naphthyl core2007In: Chemical Communications, ISSN 1359-7345, E-ISSN 1364-548X, no 1, p. 64-66Article in journal (Refereed)
    Abstract [en]

    By linking a naphthalenebisimide (NBI) unit to [Ru(bpy)3] 2+ on the naphthyl core the rate of photoinduced Ru-to-NBI electron transfer was 1000-fold increased compared to the case with a conventional linking on the nitrogen.

  • 9. Chaignon, Frederique
    et al.
    Torroba, Javier
    Blart, Errol
    Borgström, Magnus
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Chemistry, Department of Physical Chemistry. Physics, Department of Physics and Materials Science, Chemical Physics.
    Hammarström, Leif
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Chemistry, Department of Physical Chemistry. Physics, Department of Physics and Materials Science, Chemical Physics.
    Odobel, Fabrice
    Distance-independent photoinduced energy transfer over 1.1 to 2.3 nm in ruthenium tris-bipyridine-fullerene assemblies2005In: New Journal of Chemistry, Vol. 29, no 10, p. 1272-1284Article in journal (Refereed)
  • 10. Corden, Vincent A.
    et al.
    Duhme-Klair, Anne-K
    Hostachy, Sarah
    Perutz, Robin N.
    Reddig, Nicole
    Becker, Hans-Christian
    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.
    Spectroscopic and Structural Investigations Reveal the Signaling Mechanism of a Luminescent Molybdate Sensor2011In: Inorganic Chemistry, ISSN 0020-1669, E-ISSN 1520-510X, Vol. 50, no 3, p. 1105-1115Article in journal (Refereed)
    Abstract [en]

    A heteroditopic ligand H(2)-L consisting of a dihydroxybenzene (catechol)-unit linked via an amide bond to a pyridyl-unit and its methyl-protected precursor Me(2)-L were synthesized, characterized, and their photophysical properties investigated. The three accessible protonation states of the ligand, H(3)-L(+), H(2)-L, and H-L(-), showed distinct (1)H NMR, absorption and emission spectroscopic characteristics that allow pH-sensing. The spectroscopic signatures obtained act as a guide to understand the signaling mechanism of the luminescent pH and molybdate sensor [Re-(bpy)(CO)(3)(H(2)-L)](+). It was found that upon deprotonation of the 2-hydroxy group of H(2)-L, a ligand-based absorption band emerges that overlaps with the Re(d pi)-> bpy metal-to-ligand charge transfer (MLCT) band of the sensor, reducing the quantum yield for emission on excitation in the 370 nm region. In addition, deprotonation of the catechol-unit leads to quenching of the emission from the Re(d pi)-> bpy (3)MLCT state, consistent with photoinduced electron transfer from the electron-rich, deprotonated catecholate to the Re-based luminophore. Finally, reaction of 2 equiv of [Re(bpy)(CO)(3)(H(2)-L)](+) with molybdate was shown to give the zwitterionic Mo(VI) complex [MoO(2){Re(CO)(3)-(bpy)(L)}(2)], as confirmed by electrospray ionization (ESI) mass spectrometry and X-ray crystallography. The crystal structure determination revealed that two fully deprotonated sensor molecules are bound via their oxygen-donors to a cis-dioxo-MoO(2) center.

  • 11. Fortage, Jérôme
    et al.
    Göransson, Erik
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Chemical Physics.
    Blart, Errol
    Becker, Hans-Christian
    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.
    Odobel, Fabrice
    Strongly coupled zinc phthalocyanine-tin porphyrin dyad performing ultra-fast single step charge separation over a 34 Å distance2007In: Chemical Communications, ISSN 1359-7345, E-ISSN 1364-548X, no 44, p. 4629-4631Article in journal (Refereed)
    Abstract [en]

    A zinc(ii) phthalocyanine-tin(iv) porphyrin dyad with a strong electronic coupling was synthesized and upon light excitation shown to exhibit ultra-fast, long-range electron transfer in a single step.

  • 12. Georgiou, Panayiotis
    et al.
    Vincent, Jonathan
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Chemistry, Department of Photochemistry and Molecular Science. Physics, Department of Physics and Materials Science, Chemical Physics.
    Andersson, Magnus
    Wohri, Annemarie B
    Gourdon, Pontus
    Poulsen, Jens
    Davidsson, Jan
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Chemistry, Department of Photochemistry and Molecular Science. Physics, Department of Physics and Materials Science, Chemical Physics.
    Neutze, Richard
    Picosecond calorimetry: time-resolved x-ray diffraction studies of liquid CH2Cl2.2006In: J Chem Phys, ISSN 0021-9606, Vol. 124, no 23, p. 234507-Article in journal (Refereed)
  • 13.
    Gibson, Elizabeth A.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Physical and Analytical Chemistry, Physical Chemistry.
    Smeigh, Amanda L.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science.
    Le Pleux, Loic
    Fortage, Jerome
    Boschloo, Gerrit
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Physical and Analytical Chemistry, Physical Chemistry.
    Blart, Errol
    Pellegrin, Yann
    Odobel, Fabrice
    Hagfeldt, Anders
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Physical and Analytical Chemistry, Physical Chemistry.
    Hammarström, Leif
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Chemical Physics.
    A p-Type NiO-Based Dye-Sensitized Solar Cell with an Open-Circuit Voltage of 0.35 V2009In: Angewandte Chemie International Edition, ISSN 1433-7851, E-ISSN 1521-3773, Vol. 48, no 24, p. 4402-4405Article in journal (Refereed)
    Abstract [en]

    In tandem: Employing a molecular dyad and a cobalt-based electrolyte gives a threefold-increase in open-circuit voltage (VOC) for a p-type NiO device (VOC=0.35 V), and a fourfold better energy conversion efficiency. Incorporating these improvements in a TiO2/NiO tandem dye-sensitized solar cell (TDSC), results in a TDSC with a VOC=0.91 V

  • 14.
    Gibson, Elizabeth A.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Physical and Analytical Chemistry.
    Smeigh, Amanda L.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science.
    Le Pleux, Loic
    Hammarström, Leif
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Chemical Physics.
    Odobel, Fabrice
    Boschloo, Gerrit
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Physical and Analytical Chemistry, Physical Chemistry.
    Hagfeldt, Anders
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Physical and Analytical Chemistry, Physical Chemistry.
    Cobalt Polypyridyl-Based Electrolytes for p-Type Dye-Sensitized Solar Cells2011In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 115, no 19, p. 9772-9779Article in journal (Refereed)
    Abstract [en]

    A series of polypyridyl cobalt complexes with different substituents was applied as redox mediators in p-type dye-sensitized solar cells (p-DSCs), consisting of mesoporous NiO sensitized with a perylenemonoimide naphthalenediimide (PMI-NDI) dyad. The photocurrent and photovoltages of the devices were found to depend on the steric bulk of the redox species rather than their electrochemical potential. Bulky substituents were found to slow the detrimental charge recombination reactions between holes in the NiO semiconductor and the reduced form of the redox couple. The open-circuit potential (V-OC) of each of the devices was superior to the equivalent PMI-NDIsensitized p-DSCs containing the triiodide/iodide redox couple.

  • 15.
    Göransson, Erik
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Chemical Physics.
    Boixel, Julien
    Monnereau, Cyrille
    Blart, Errol
    Pellegrin, Yann
    Becker, Hans-Christian
    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.
    Odobel, Fabrice
    Photoinduced Electron Transfer in Zn(II)porphyrin-Bridge-Pt(II)acetylide Complexes: Variation in Rate with Anchoring Group and Position of the Bridge2010In: Inorganic Chemistry, ISSN 0020-1669, E-ISSN 1520-510X, Vol. 49, no 21, p. 9823-9832Article in journal (Refereed)
    Abstract [en]

    The synthesis and photophysical characterization of two sets of zinc porphyrin platinum acetylide complexes are reported. The two sets of molecules differ in the way the bridging phenyl-ethynyl unit is attached to the porphyrin ring. One set is attached via an ethynyl unit on the beta position, while the other set is attached via a phenyl unit on the meso position of the porphyrin. These were compared with previously studied complexes where attachment was made via an ethynyl unit on the meso position. Femtosecond transient absorption measurements showed in all systems a rapid quenching of the porphyrin singlet state. Electron transfer is suggested as the quenching mechanism, followed by an even faster recombination to form both the porphyrin ground and triplet excited states. This is supported by the variation in quenching rate and porphyrin triplet yield with solvent polarity, and the observation of an intermediate state in the meso-phenyl linked systems. The different linking motifs between the dyads resulted in significant variations in electron transfer rates.

  • 16.
    Hammarström, Leif
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Chemical Physics.
    Johansson, Olof
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Molecular Biomimetics.
    Expanded bite angles in tridentate ligands: improving the photophysical properties in bistridentate Ru-II polypyridine complexes2010In: Coordination chemistry reviews, ISSN 0010-8545, E-ISSN 1873-3840, Vol. 254, no 21-22, p. 2546-2559Article in journal (Refereed)
    Abstract [en]

    Bistridentate metal complexes as photosensitizers are ideal building blocks in the construction of rodlike isomer-free assemblies for intramolecular photoinduced charge separation. Approaches to obtain long-lived luminescent metal-to-ligand charge transfer excited states in bistridentate Run polypyridine complexes via the manipulation of metal-centered state energies are discussed. Following an introduction to general strategies to prolong the excited state lifetimes, more recent work is explored in detail where tridentate ligands with expanded 2,2':6',2 ''-terpyridine cores are utilized. The synthesis of these tridentate ligands and their corresponding Ru-II complexes is covered. Bistridentate Run complexes with microsecond metal-to-ligand charge transfer excited state lifetimes are described, and are used in electron donor-photosensitizer-electron acceptor assemblies for efficient vectorial photoinduced charge separation.

  • 17.
    Hammarström, Leif
    et al.
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Chemistry, Department of Photochemistry and Molecular Science. Physics, Department of Physics and Materials Science, Chemical Physics. Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Chemistry, Department of Photochemistry and Molecular Science, Molecular Biomimetics.
    Johansson, Olof
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Chemistry, Department of Photochemistry and Molecular Science. Physics, Department of Physics and Materials Science, Chemical Physics. Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Chemistry, Department of Photochemistry and Molecular Science, Molecular Biomimetics.
    Magnuson, Ann
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Chemistry, Department of Photochemistry and Molecular Science. Physics, Department of Physics and Materials Science, Chemical Physics. Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Chemistry, Department of Photochemistry and Molecular Science, Molecular Biomimetics.
    Artificial Photosynthesis Edited by Anthony F. Collings and Christa Critchley2006In: Angewandte Chemie, International Edition, 2006Chapter in book (Other (popular scientific, debate etc.))
  • 18.
    Hammarström, Leif
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Chemical Physics.
    Styring, Stenbjörn
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Molecular Biomimetics.
    Proton-coupled electron transfer of tyrosines in Photosystem II and model systems for artificial photosynthesis: the role of a redox-active link between catalyst and photosensitizer2011In: Energy & Environmental Science, ISSN 1754-5692, E-ISSN 1754-5706, Vol. 4, no 7, p. 2379-2388Article in journal (Refereed)
    Abstract [en]

    Water oxidation in Photosystem II is dependent on a particular amino acid residue, Tyrosine(Z). This is a redox intermediate in steady state oxygen evolution and transfers electrons from the water splitting CaMn4 cluster to the central chlorophyll radical P-680(+). This Perspective discusses the functional principles of Tyrosine(Z) as a proton-coupled redox active link, as well as mechanistic studies of synthetic model systems and implications for artificial photosynthesis. Experimental studies of temperature dependence and kinetic isotope effects are important tools to understand these reactions. We emphasize the importance of proton transfer distance and hydrogen bond dynamics that are responsible for variation in the rate of PCET by several orders of magnitude. The mechanistic principles discussed and their functional significance are not limited to tyrosine and biological systems, but are important to take into account when constructing artificial photosynthetic systems. Of particular importance is the role of proton transfer management in water splitting and solar fuel catalysis.

  • 19.
    Hammarström, Leif
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Chemical Physics.
    Winkler, Jay R.
    Gray, Harry B.
    Styring, Stenbjörn
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Molecular Biomimetics.
    Shedding Light on Solar Fuel Efficiencies2011In: Science, ISSN 0036-8075, E-ISSN 1095-9203, Vol. 333, no 6040, p. 288-288Article in journal (Refereed)
  • 20.
    Huang, Ping
    et al.
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Chemistry, Department of Photochemistry and Molecular Science. Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Chemistry, Department of Photochemistry and Molecular Science, Molecular Biomimetics. Physics, Department of Physics and Materials Science, Chemical Physics.
    Shaikh, Nizamuddin
    Anderlund, Magnus F
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Chemistry, Department of Photochemistry and Molecular Science. Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Chemistry, Department of Photochemistry and Molecular Science, Molecular Biomimetics. Physics, Department of Physics and Materials Science, Chemical Physics.
    Styring, Stenbjörn
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Chemistry, Department of Photochemistry and Molecular Science. Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Chemistry, Department of Photochemistry and Molecular Science, Molecular Biomimetics. Physics, Department of Physics and Materials Science, Chemical Physics.
    Hammarström, Leif
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Chemistry, Department of Photochemistry and Molecular Science. Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Chemistry, Department of Photochemistry and Molecular Science, Molecular Biomimetics. Physics, Department of Physics and Materials Science, Chemical Physics.
    Consistent simulation of X- and Q-band EPR spectra of an unsymmetric dinuclear Mn2(II,III) complex.2006In: J Inorg Biochem, ISSN 0162-0134, Vol. 100, no 5-6, p. 1139-46Article in journal (Refereed)
  • 21.
    Irebo, Tania
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Chemical Physics.
    Proton-Coupled Electron Transfer from Hydrogen-Bonded Phenols2010Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Proton-coupled electron transfer (PCET) is one of the elementary reactions occurring in many chemical and biological systems, such as photosystem II where the oxidation of tyrosine (TyrZ) is coupled to deprotonation of the phenolic proton. This reaction is here modelled by the oxidation of a phenol covalently linked to a Ru(bpy)32+-moitey, which is photo-oxidized by a laser flash-quench method. This model system is unusual as mechanism of PCET is studied in a unimolecular system in water solution. Here we address the question how the nature of the proton accepting base and its hydrogen bond to phenol influence the PCET reaction.

    In the first part we investigate the effect of an internal hydrogen bond PCET from. Two similar phenols are compared. For both these the proton accepting base is a carboxylate group linked to the phenol on the ortho-position directly or via a methylene group. On the basis of kinetic and thermodynamic arguments it is suggested that the PCET from these occurs via a concerted electron proton transfer (CEP). Moreover, numerical modelling of the kinetic data provides an in-depth analysis of this CEP reaction, including promoting  vibrations  along the O–H–O coordinate that are required to explain the data.

    The second part describes the study on oxidation of phenol where either water or an external base the proton acceptor. The pH-dependence of the kinetics reveals four mechanistic regions for PCET within the same molecule when water is the base. It is shown that the competition between the mechanisms can be tuned by the strength of the oxidant. Moreover, these studies reveal the conditions that may favour a buffer-assisted PCET over that with deprotonation to water solution.

    List of papers
    1. The rate ladder of proton-coupled tyrosine oxidation in water: A systematic dependence on hydrogen bonds and protonation state
    Open this publication in new window or tab >>The rate ladder of proton-coupled tyrosine oxidation in water: A systematic dependence on hydrogen bonds and protonation state
    2008 (English)In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 130, no 29, p. 9194-+Article in journal (Refereed) Published
    Abstract [en]

    Proton coupled electron transfer (PCET) from tyrosine covalently linked to Ru(bPY)(3)(2+) has been studied with laser flash-quench techniques. Two new complexes with internal hydrogen bonding bases to the phenolic proton have been synthesized. Depending on the hydrogen bonding and protonation situation the rate constant of PCET spanned over 5 orders of magnitude and revealed a systematic dependence on pH. This resulted in a previously predicted "rate ladder" scheme: (i) pH dependent concerted electron-proton transfer (CEP) with deprotonation to bulk water, giving low PCET rates, (ii) pH independent CEP with deprotonation to the internal base, giving intermediate PCET rates, and (iii) pure electron transfer from tyrosinate, giving high rates. This behavior is reminiscent of Y-z oxidation in Mn-depleted and native photosystem II. The study also revealed important differences in rates between phenols with strong and weak hydrogen bonds, and for the latter a hydrogen bond-gated PCET was observed.

    National Category
    Chemical Sciences
    Identifiers
    urn:nbn:se:uu:diva-109962 (URN)10.1021/ja802076v (DOI)000257796500008 ()
    Available from: 2009-11-02 Created: 2009-11-02 Last updated: 2017-12-12Bibliographically approved
    2. Proton-coupled electron transfer of tyrosine oxidation: buffer dependence and parallel mechanisms
    Open this publication in new window or tab >>Proton-coupled electron transfer of tyrosine oxidation: buffer dependence and parallel mechanisms
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    2007 (English)In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 129, no 50, p. 15462-15464Article in journal (Refereed) Published
    Abstract [en]

    The proton-coupled electron transfer (PCET) from tyrosine covalently linked to a metal complex has been studied. The reaction was induced by laser flash excitation of the metal complex, and PCET was bidirectional, with electron transfer to the excited or flash-quenched oxidized metal complex and proton transfer to water or added buffers in the solution. We found a competition between three different PCET mechanisms: (1) A concerted PCET with water as the proton acceptor, which indeed shows a pH-dependence as earlier reported (Sjödin, M.; Styring, S.; Åkermark, B.; Sun, L.; Hammarström, L. J. Am. Chem. Soc. 2000, 122, 3932); (2) a stepwise electron transfer-proton transfer (ETPT) that is pH-independent; (3) a buffer-assisted concerted PCET. The relative importance of reaction 2 increases with oxidant strength, while that of reaction 1 increases with pH. At higher buffer concentrations reaction 3 becomes important, and the rate follows the expected first-order dependence on the concentration of the buffer base. Most importantly, the pH-dependence of reaction 1, with a slope of 0.4-0.5 in a plot of log k vs pH, is independent of buffer and cannot be explained by reaction schemes with simple first-order dependencies on [OH-], [H3O+], or buffer species.

    Keywords
    Chemistry, Multidisciplinary
    National Category
    Chemical Sciences
    Identifiers
    urn:nbn:se:uu:diva-12424 (URN)10.1021/ja073012u (DOI)000251581900026 ()18027937 (PubMedID)
    Available from: 2007-12-18 Created: 2007-12-18 Last updated: 2017-12-11Bibliographically approved
    3. Spanning Four Mechanistic Regions of Intramolecular Proton-Coupled Electron Transfer in a Ru(bpy)32+-Tyrosine Complex
    Open this publication in new window or tab >>Spanning Four Mechanistic Regions of Intramolecular Proton-Coupled Electron Transfer in a Ru(bpy)32+-Tyrosine Complex
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    2012 (English)In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 134, no 39, p. 16247-16254Article in journal (Refereed) Published
    Abstract [en]

    Proton-coupled electron transfer (PCET) from tyrosine (TyrOH) to a covalently linked [Ru(bpy)(3)](2+) photosensitizer in aqueous media has been systematically reinvestigated by laser flash-quench kinetics as a model system for PCET in radical enzymes and in photochemical energy conversion. Previous kinetic studies on Ru-TyrOH molecules (Sjodin et al. J. Am. Chem. Soc. 2000, 122, 3932; Irebo et al. J. Am. Chem. Soc. 2007, 129, 15462) have established two mechanisms. Concerted electron-proton (CEP) transfer has been observed when pH < pK(a)(TyrOH), which is pH-dependent but not first-order in [OH-] and not dependent on the buffer concentration when it is sufficiently low (less than ca. 5 mM). In addition, the pH-independent rate constant for electron transfer from tyrosine phenolate (TyrO(-)) was reported at pH >10. Here we compare the PCET rates and kinetic isotope effects (k(H)/k(D)) of four Ru-TyrOH molecules with varying Ru-III/II oxidant strengths over a pH range of 1-12.5. On the basis of these data, two additional mechanistic regimes were observed and identified through analysis of kinetic competition and kinetic isotope effects (KIE): (i) a mechanism dominating at low pH assigned to a stepwise electron-first PCET and (ii) a stepwise proton-first PCET with OH- as proton acceptor that dominates around pH = 10. The effect of solution pH and electrochemical potential of the Ru-III/II oxidant on the competition between the different mechanisms is discussed. The systems investigated may serve as models for the mechanistic diversity of PCET reactions in general with water (H2O, OH-) as primary proton acceptor.

    Keywords
    proton-coupled electron transfer, phenol oxidation, artificial photosynthesis
    National Category
    Chemical Sciences
    Research subject
    Physical Chemistry
    Identifiers
    urn:nbn:se:uu:diva-112056 (URN)10.1021/ja3053859 (DOI)000309335000029 ()
    Note

    De 2 första författarna delar förstaförfattarskapet.

    Available from: 2010-01-07 Created: 2010-01-07 Last updated: 2017-12-12Bibliographically approved
    4. The Kinetic Effect of Internal Hydrogen Bonds on Proton-Coupled Electron Transfer from Phenols: A Theoretical Analysis with Modeling of Experimental Data
    Open this publication in new window or tab >>The Kinetic Effect of Internal Hydrogen Bonds on Proton-Coupled Electron Transfer from Phenols: A Theoretical Analysis with Modeling of Experimental Data
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    2009 (English)In: Journal of Physical Chemistry B, ISSN 1520-6106, E-ISSN 1520-5207, Vol. 113, no 50, p. 16214-16225Article in journal (Refereed) Published
    Abstract [en]

    Proton-coupled electron transfer (PCET) was studied in two biomimetic covalently linked Ru(bpy)3−tyrosine complexes with the phenolic proton hydrogen-bonded to an internal carboxylate group. The phenolic group is either a salicylic acid (o-hydroxybenzoic acid, SA) or an o-hydroxyphenyl-acetic acid (PA), where the former gives a resonance-assisted hydrogen bond. Transient absorption data allowed direct determination of the rate constant for these intramolecular, bidirectional, and concerted PCET (CEP) reactions, as a function of temperature and H/D isotope. We found, unexpectedly, that the hydrogen bond in SA is in fact weaker than the hydrogen bond in the complex with PA, which forced us to reassess an earlier hypothesis that the proton coupling term for CEP with SA is increased by a stronger hydrogen bond. Consequently, the kinetic data was modeled numerically using a quantum mechanical rate expression. Sufficient experimentally determined observables were available to give robust and well-determined parameter values. This analysis, coupled with DFT/B3LYP and MP2 calculations and MD simulations, gave a detailed insight into the parameters that control the CEP reactions, and the effect of internal hydrogen bonds. We observed that a model with a static proton-tunneling distance is unable to describe the reaction correctly, requiring unrealistic values for the equilibrium proton-tunneling distances. Instead, when promoting vibrations that modulate the proton donor−acceptor distance were included, satisfactory fits to the experimental data were obtained, with parameter values that agree with DFT calculations and MD simulations. According to these results, it is in fact the weaker hydrogen bond of SA which increases the proton coupling. The inner reorganization energy of the phenolic groups is a significant factor contributing to the CEP barriers, but this is reduced by the hydrogen bonds to 0.35 and 0.50 eV for the two complexes. The promoting vibrations increase the rate of CEP by over 2 orders of magnitude, and dramatically reduce the kinetic isotope effect from ca. 40 for the static case to a modest value of 2−3.

    National Category
    Chemical Sciences
    Identifiers
    urn:nbn:se:uu:diva-111831 (URN)10.1021/jp9048633 (DOI)000272560100015 ()
    Available from: 2009-12-22 Created: 2009-12-22 Last updated: 2017-12-12Bibliographically approved
    5. Kinetic effects of hydrogen bonds on proton-coupled electron transfer from phenols
    Open this publication in new window or tab >>Kinetic effects of hydrogen bonds on proton-coupled electron transfer from phenols
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    2006 (English)In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 128, no 40, p. 13076-13083Article in journal (Refereed) Published
    Abstract [en]

    The kinetics and mechanism of proton-coupled electron transfer (PCET) from a series of phenols to a laser flash generated [Ru(bpy)(3)](3+) oxidant in aqueous solution was investigated. The reaction followed a concerted electron-proton transfer mechanism (CEP), both for the substituted phenols with an intramolecular hydrogen bond to a carboxylate group and for those where the proton was directly transferred to water. Without internal hydrogen bonds the concerted mechanism gave a characteristic pH-dependent rate for the phenol form that followed a Marcus free energy dependence, first reported for an intramolecular PCET in Sjodin, M. et al. J. Am. Chem. Soc. 2000, 122, 3932-3962 and now demonstrated also for a bimolecular oxidation of unsubstituted phenol. With internal hydrogen bonds instead, the rate was no longer pH-dependent, because the proton was transferred to the carboxylate base. The results suggest that while a concerted reaction has a relatively high reorganization energy (lambda), this may be significantly reduced by the hydrogen bonds, allowing for a lower barrier reaction path. It is further suggested that this is a general mechanism by which proton-coupled electron transfer in radical enzymes and model complexes may be promoted by hydrogen bonding. This is different from, and possibly in addition to, the generally suggested effect of hydrogen bonds on PCET in enhancing the proton vibrational wave function overlap between the reactant and donor states. In addition we demonstrate how the mechanism for phenol oxidation changes from a stepwise electron transfer-proton transfer with a stronger oxidant to a CEP with a weaker oxidant, for the same series of phenols. The hydrogen bonded CEP reaction may thus allow for a low energy barrier path that can operate efficiently at low driving forces, which is ideal for PCET reactions in biological systems.

    National Category
    Chemical Sciences
    Identifiers
    urn:nbn:se:uu:diva-83646 (URN)10.1021/ja063264f (DOI)000241030500024 ()17017787 (PubMedID)
    Available from: 2006-11-07 Created: 2006-11-07 Last updated: 2017-12-14Bibliographically approved
  • 22.
    Irebo, Tania
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science.
    Reece, Steven Y.
    Sjödin, Martin
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science.
    Nocera, Daniel G.
    Hammarström, Leif
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Chemical Physics.
    Proton-coupled electron transfer of tyrosine oxidation: buffer dependence and parallel mechanisms2007In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 129, no 50, p. 15462-15464Article in journal (Refereed)
    Abstract [en]

    The proton-coupled electron transfer (PCET) from tyrosine covalently linked to a metal complex has been studied. The reaction was induced by laser flash excitation of the metal complex, and PCET was bidirectional, with electron transfer to the excited or flash-quenched oxidized metal complex and proton transfer to water or added buffers in the solution. We found a competition between three different PCET mechanisms: (1) A concerted PCET with water as the proton acceptor, which indeed shows a pH-dependence as earlier reported (Sjödin, M.; Styring, S.; Åkermark, B.; Sun, L.; Hammarström, L. J. Am. Chem. Soc. 2000, 122, 3932); (2) a stepwise electron transfer-proton transfer (ETPT) that is pH-independent; (3) a buffer-assisted concerted PCET. The relative importance of reaction 2 increases with oxidant strength, while that of reaction 1 increases with pH. At higher buffer concentrations reaction 3 becomes important, and the rate follows the expected first-order dependence on the concentration of the buffer base. Most importantly, the pH-dependence of reaction 1, with a slope of 0.4-0.5 in a plot of log k vs pH, is independent of buffer and cannot be explained by reaction schemes with simple first-order dependencies on [OH-], [H3O+], or buffer species.

  • 23.
    Johannissen, Linus O.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science.
    Irebo, Tania
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Chemical Physics.
    Sjödin, Martin
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science.
    Johansson, Olof
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science.
    Hammarström, Leif
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Chemical Physics.
    The Kinetic Effect of Internal Hydrogen Bonds on Proton-Coupled Electron Transfer from Phenols: A Theoretical Analysis with Modeling of Experimental Data2009In: Journal of Physical Chemistry B, ISSN 1520-6106, E-ISSN 1520-5207, Vol. 113, no 50, p. 16214-16225Article in journal (Refereed)
    Abstract [en]

    Proton-coupled electron transfer (PCET) was studied in two biomimetic covalently linked Ru(bpy)3−tyrosine complexes with the phenolic proton hydrogen-bonded to an internal carboxylate group. The phenolic group is either a salicylic acid (o-hydroxybenzoic acid, SA) or an o-hydroxyphenyl-acetic acid (PA), where the former gives a resonance-assisted hydrogen bond. Transient absorption data allowed direct determination of the rate constant for these intramolecular, bidirectional, and concerted PCET (CEP) reactions, as a function of temperature and H/D isotope. We found, unexpectedly, that the hydrogen bond in SA is in fact weaker than the hydrogen bond in the complex with PA, which forced us to reassess an earlier hypothesis that the proton coupling term for CEP with SA is increased by a stronger hydrogen bond. Consequently, the kinetic data was modeled numerically using a quantum mechanical rate expression. Sufficient experimentally determined observables were available to give robust and well-determined parameter values. This analysis, coupled with DFT/B3LYP and MP2 calculations and MD simulations, gave a detailed insight into the parameters that control the CEP reactions, and the effect of internal hydrogen bonds. We observed that a model with a static proton-tunneling distance is unable to describe the reaction correctly, requiring unrealistic values for the equilibrium proton-tunneling distances. Instead, when promoting vibrations that modulate the proton donor−acceptor distance were included, satisfactory fits to the experimental data were obtained, with parameter values that agree with DFT calculations and MD simulations. According to these results, it is in fact the weaker hydrogen bond of SA which increases the proton coupling. The inner reorganization energy of the phenolic groups is a significant factor contributing to the CEP barriers, but this is reduced by the hydrogen bonds to 0.35 and 0.50 eV for the two complexes. The promoting vibrations increase the rate of CEP by over 2 orders of magnitude, and dramatically reduce the kinetic isotope effect from ca. 40 for the static case to a modest value of 2−3.

  • 24.
    Johansson, Olof
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Physical Chemistry. Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Molecular Biomimetics. Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Chemical Physics. Avdelningen för molekylär biomimetik.
    Lomoth, Reiner
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Physical Chemistry. Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Molecular Biomimetics. Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Chemical Physics.
    Rapid electrochemically induced linkage isomerism in a ruthenium(II) polypyridyl complex2005In: Chemical Communications, ISSN 1359-7345, E-ISSN 1364-548X, no 12, p. 1578-80Article in journal (Refereed)
  • 25.
    Jäger, Michael
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Molecular Biomimetics.
    Smeigh, Amanda
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Chemical Physics.
    Lombeck, Florian
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science.
    Gorls, Helmar
    Collin, Jean-Paul
    Sauvage, Jean-Pierre
    Hammarström, Leif
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Chemical Physics.
    Johansson, Olof
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Molecular Biomimetics.
    Cyclometalated Ru-II Complexes with Improved Octahedral Geometry: Synthesis and Photophysical Properties2010In: Inorganic Chemistry, ISSN 0020-1669, E-ISSN 1520-510X, Vol. 49, no 2, p. 374-376Article in journal (Refereed)
    Abstract [en]

    Cyclometalated bis-tridentate ruthenium(II) complexes incorporating 2,6-diquinolin-8-ylpyridine ligands and exhibiting broad visible absorptions are described. A [Ru(N boolean AND N boolean AND N)(N boolean AND C boolean AND N)](+) complex based only on ligands with expanded bite angles has a metal-to-ligand charge-transfer excited-state lifetime of 16 ns, which is attributed to a strong ligand field and therefore reduced deactivation via metal-centered states.

  • 26.
    Karlsson, Susanne
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Chemical Physics.
    Single and Accumulative Electron Transfer – Prerequisites for Artificial Photosynthesis2010Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Photoinduced electron transfer is involved in a number of photochemical and photobiological processes. One example of this is photosynthesis, where the absorption of sunlight leads to the formation of charge-separated states by electron transfer. The redox equivalents built up by successive photoabsorption and electron transfer is further used for the oxidation of water and reduction of carbon dioxide to sugars. The work presented in this thesis is part of an interdisciplinary effort aiming at a functional mimic of photosynthesis. The goal of this project is to utilize sunlight to produce renewable fuels from sun and water. Specifically, this thesis concerns photoinduced electron transfer in donor(D)-photosensitizer(P)-acceptor(A) systems, in mimic of the primary events of photosynthesis.

    The absorption of a photon typically leads to transfer of a single electron, i.e., charge separation to produce a single electron-hole pair. This fundamental process was studied in several molecular systems. The purpose of these studies was optimization of single electron transfer as to obtain charge separation in high yields, with minimum losses to competing photoreactions such as energy transfer. Also, the lifetime of the charge separated state and the confinement of the electron and hole in three-dimensional space are important in practical applications. This led us to explore molecular motifs for linear arrays based on Ru(II)bis-tridentate and Ru(II)tris-bidentate complexes.

    The target multi-electron catalytic reactions of water-splitting and fuel production require a build-up of redox equivalents upon successive photoexcitation and electron transfer events. The possibilities and challenges associated with such processes in molecular systems were investigated. One of the studied systems was shown to accumulate two electrons and two holes upon two successive excitations, without sacrificial redox agents and with minimum yield losses. From these studies, we have gained better understanding of the obstacles associated with step-wise photoaccumulation of charge and how to overcome them.

    List of papers
    1. How Close Can You Get?: Studies of Ultrafast Light-Induced Processes in Ruthenium-[60] Fullerene Dyads with Short Pyrazolino and Pyrrolidino Links
    Open this publication in new window or tab >>How Close Can You Get?: Studies of Ultrafast Light-Induced Processes in Ruthenium-[60] Fullerene Dyads with Short Pyrazolino and Pyrrolidino Links
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    2008 (English)In: Inorganic Chemistry, ISSN 0020-1669, E-ISSN 1520-510X, Vol. 47, no 16, p. 7286-7294Article in journal (Refereed) Published
    Abstract [en]

    Two pyrazoline- and one pyrrolidine-bridged Ru(II)bipyridine-[60]fullerene dyads have been prepared and studied by ultrafast time-resolved spectroscopy. A silver-assisted synthesis route, in which Ag(I) removes the chlorides from the precursor complex Ru(bpy)(2)Cl-2 facilitates successful coordination of the [60]fullerene-substituted third ligand. Upon light excitation of the ruthenium moiety, the emission was strongly quenched by the fullerene. The main quenching mechanism is an exceptionally fast direct energy transfer (k(obs) > , 1 x 10(12) s(-1) in the pyrazoline-bridged dyads), resulting in population of the lowest excited triplet state of fullerene. No evidence for electron transfer was found, despite the extraordinarily short donor-acceptor distance that could kinetically favor that process. The observations have implications on the ongoing development of devices built from Ru-polypyridyl complexes and nanostructured carbon, such as C-60 or nanotubes.

    National Category
    Other Basic Medicine
    Research subject
    Organic Chemistry
    Identifiers
    urn:nbn:se:uu:diva-87346 (URN)10.1021/ic800168d (DOI)000258332900030 ()
    Available from: 2008-10-07 Created: 2008-10-07 Last updated: 2018-01-12Bibliographically approved
    2. Vectorial Electron Transfer in Donor-Photosensitizer-Acceptor Triads Based on Novel Bis-tridentate Ruthenium Polypyridyl Complexes
    Open this publication in new window or tab >>Vectorial Electron Transfer in Donor-Photosensitizer-Acceptor Triads Based on Novel Bis-tridentate Ruthenium Polypyridyl Complexes
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    2010 (English)In: Chemistry - A European Journal, ISSN 0947-6539, E-ISSN 1521-3765, Vol. 16, no 9, p. 2830-2842Article in journal (Refereed) Published
    Abstract [en]

    The first examples of rodlikedonor–photosensitizer–acceptor arrays based on bis-2,6-di(quinolin-8-yl)pyridineRuII complexes 1a and 3a for photoinduced electron transfer have been synthesized and investigated. The complexes are synthesized in a convergent manner and are isolated as linear, single isomers. Time-resolved absorption spectroscopy reveals long-lived, photoinduced charge-separated states(tCSS (1a)=140 ns, tCSS (3a)=200 ns) formed by stepwise electron transfer.The overall yields of charge separation (Yield 50% for complex 1a and Yield 95% for complex 3a) are unprecedented for bis-tridentate RuII polypyridyl complexes.This is attributed to the longlived excited state of the [Ru(dqp)2]2+ complex combined with fast electron transfer from the donor moiety following the initial charge separation. The rodlike arrangement of donor and acceptor gives controlled, vectorial electron transfer, free from the complications of stereoisomeric diversity. Thus, such arrays provide an excellent system for the study of photoinduced electron transfer and, ultimately, the harvesting of solar energy.

    Place, publisher, year, edition, pages
    Weinhem: Wiley-VCH, 2010
    Keywords
    donor-acceptor systems, electron transfer, photochemistry, ruthenium, tridentate ligands
    National Category
    Physical Chemistry
    Identifiers
    urn:nbn:se:uu:diva-113609 (URN)10.1002/chem.200902716 (DOI)000275943000024 ()20087914 (PubMedID)
    Available from: 2010-03-22 Created: 2010-02-01 Last updated: 2017-12-12Bibliographically approved
    3. Towards [Ru(bpy)3]2+-Based Linear Donor (D)-Photosensitizer (P)-Acceptor (A) Arrays: Using the 5,5´-Positions in [Ru(bpy)3]2+-Benzoquinone Dyads
    Open this publication in new window or tab >>Towards [Ru(bpy)3]2+-Based Linear Donor (D)-Photosensitizer (P)-Acceptor (A) Arrays: Using the 5,5´-Positions in [Ru(bpy)3]2+-Benzoquinone Dyads
    Show others...
    Manuscript (Other academic)
    Identifiers
    urn:nbn:se:uu:diva-98070 (URN)
    Available from: 2009-02-04 Created: 2009-02-04 Last updated: 2010-04-07Bibliographically approved
    4. Double-pulse Excitation of a Mn2-Ru(II)-Naphthalenediimide Triad: Challenges for Accumulative Electron Transfer
    Open this publication in new window or tab >>Double-pulse Excitation of a Mn2-Ru(II)-Naphthalenediimide Triad: Challenges for Accumulative Electron Transfer
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    (English)Manuscript (preprint) (Other academic)
    National Category
    Other Basic Medicine
    Research subject
    Chemistry with specialization in Chemical Physics
    Identifiers
    urn:nbn:se:uu:diva-113613 (URN)
    Available from: 2010-04-07 Created: 2010-02-01 Last updated: 2018-01-12
    5. Accumulative charge separation inspired by photosynthesis
    Open this publication in new window or tab >>Accumulative charge separation inspired by photosynthesis
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    2010 (English)In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 132, no 51, p. 17977-17979Article in journal (Refereed) Published
    Abstract [en]

    Molecular systems that follow the functional principles of photosynthesis have attracted increasing attention as a method for the direct production of solar fuels. This could give a major carbon-neutral energy contribution to our future society. An outstanding challenge in this research is to couple the light-induced charge separation (which generates a single electron-hole pair) to the multielectron processes of water oxidation and fuel generation. New design considerations are needed to allow for several cycles of photon absorption and charge separation of a single artificial photosystem. Here we demonstrate a molecular system with a regenerative photosensitizer that shows two successive events of light-induced charge separation, leading to high-yield accumulation of redox equivalents on single components without sacrificial agents.

    National Category
    Chemical Sciences
    Research subject
    Chemistry with specialization in Chemical Physics
    Identifiers
    urn:nbn:se:uu:diva-122184 (URN)10.1021/ja104809x (DOI)000285818700001 ()21138258 (PubMedID)
    Available from: 2010-04-07 Created: 2010-04-07 Last updated: 2017-12-12Bibliographically approved
    6. Multiple Excitation Studies of Ru(II)polypyridyl-Oligotriarylamine Dye-Nanocrystalline TiO2 Systems for Photoinduced Charge Accumulation
    Open this publication in new window or tab >>Multiple Excitation Studies of Ru(II)polypyridyl-Oligotriarylamine Dye-Nanocrystalline TiO2 Systems for Photoinduced Charge Accumulation
    Show others...
    (English)Manuscript (preprint) (Other (popular science, discussion, etc.))
    Research subject
    Chemistry with specialization in Chemical Physics
    Identifiers
    urn:nbn:se:uu:diva-122185 (URN)
    Available from: 2010-04-07 Created: 2010-04-07 Last updated: 2010-04-07
  • 27.
    Karlsson, Susanne
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Chemical Physics.
    Boixel, Julien
    Chimie et Inerdiciplinarité, Synthèse, Analyse, Modélisation, Université de Nantes.
    Pelegrin, Yann
    Chimie et Inerdiciplinarité, Synthèse, Analyse, Modélisation, Université de Nantes.
    Becker, Hans-Christian
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Chemical Physics.
    Blart, Errol
    Chimie et Inerdiciplinarité, Synthèse, Analyse, Modélisation, Université de Nantes.
    Odobel, Fabrice
    Chimie et Inerdiciplinarité, Synthèse, Analyse, Modélisation, Université de Nantes.
    Hammarström, Leif
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Chemical Physics.
    Multiple Excitation Studies of Ru(II)polypyridyl-Oligotriarylamine Dye-Nanocrystalline TiO2 Systems for Photoinduced Charge AccumulationManuscript (preprint) (Other (popular science, discussion, etc.))
  • 28.
    Karlsson, Susanne
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Chemical Physics.
    Boixel, Julien
    Chimie et Interdisciplinarité, Synthèse, Analyse, Modélisation, Université de Nantes.
    Pelegrin, Yann
    Chimie et Interdisciplinarité, Synthèse, Analyse, Modélisation, Université de Nantes.
    Blart, Errol
    Chimie et Interdisciplinarité, Synthèse, Analyse, Modélisation, Université de Nantes.
    Becker, Hans-Christian
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Chemical Physics.
    Odobel, Fabrice
    Chimie et Interdisciplinarité, Synthèse, Analyse, Modélisation, Université de Nantes.
    Hammarström, Leif
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Chemical Physics.
    Accumulative charge separation inspired by photosynthesis2010In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 132, no 51, p. 17977-17979Article in journal (Refereed)
    Abstract [en]

    Molecular systems that follow the functional principles of photosynthesis have attracted increasing attention as a method for the direct production of solar fuels. This could give a major carbon-neutral energy contribution to our future society. An outstanding challenge in this research is to couple the light-induced charge separation (which generates a single electron-hole pair) to the multielectron processes of water oxidation and fuel generation. New design considerations are needed to allow for several cycles of photon absorption and charge separation of a single artificial photosystem. Here we demonstrate a molecular system with a regenerative photosensitizer that shows two successive events of light-induced charge separation, leading to high-yield accumulation of redox equivalents on single components without sacrificial agents.

  • 29.
    Karlsson, Susanne
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Chemical Physics.
    Streich, Daniel
    Johansson, Olof
    Anderlund, Magnus
    Becker, Hans-Christian
    Hammarström, Leif
    Double-pulse Excitation of a Mn2-Ru(II)-Naphthalenediimide Triad: Challenges for Accumulative Electron TransferManuscript (preprint) (Other academic)
  • 30.
    Kaur-Ghumaan, Sandeep
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Molecular Biomimetics.
    Schwartz, Lennart
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Molecular Biomimetics.
    Lomoth, Reiner
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Chemical Physics.
    Stein, Matthias
    Ott, Sascha
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Molecular Biomimetics.
    Catalytic Hydrogen Evolution from Mononuclear Iron(II) Carbonyl Complexes as Minimal Functional Models of the [FeFe] Hydrogenase Active Site2010In: Angewandte Chemie International Edition, ISSN 1433-7851, E-ISSN 1521-3773, Vol. 49, no 43, p. 8033-8036Article in journal (Refereed)
    Abstract [en]

    How much iron does it take? Mononuclear complexes [FeII(3,6-R2bdt)(CO)2(PMe3)2] (bdt=1,2-C6H4(S)2; R=H, Cl) can be reversibly protonated at the sulfur ligands, can catalyze the electrochemical reduction of protons, and are thus minimal functional models of the [FeFe] hydrogenases (see scheme). DFT calculations show that cleavage of an FeS bond leads to the generation of a free coordination site, which is crucial for the formation of hydrides that are key intermediates in the generation of hydrogen.

  • 31.
    Kumar, Rohan J
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Molecular Biomimetics.
    Karlsson, Susanne
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Chemical Physics.
    Streich, Daniel
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Chemical Physics.
    Rolandini Jensen, Alice
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Chemical Physics.
    Jäger, Michael
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Molecular Biomimetics.
    Becker, Hans-Christian
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Chemical Physics.
    Bergquist, Jonas
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Physical and Analytical Chemistry, Analytical Chemistry.
    Johansson, Olof
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Molecular Biomimetics.
    Hammarström, Leif
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Chemical Physics.
    Vectorial Electron Transfer in Donor-Photosensitizer-Acceptor Triads Based on Novel Bis-tridentate Ruthenium Polypyridyl Complexes2010In: Chemistry - A European Journal, ISSN 0947-6539, E-ISSN 1521-3765, Vol. 16, no 9, p. 2830-2842Article in journal (Refereed)
    Abstract [en]

    The first examples of rodlikedonor–photosensitizer–acceptor arrays based on bis-2,6-di(quinolin-8-yl)pyridineRuII complexes 1a and 3a for photoinduced electron transfer have been synthesized and investigated. The complexes are synthesized in a convergent manner and are isolated as linear, single isomers. Time-resolved absorption spectroscopy reveals long-lived, photoinduced charge-separated states(tCSS (1a)=140 ns, tCSS (3a)=200 ns) formed by stepwise electron transfer.The overall yields of charge separation (Yield 50% for complex 1a and Yield 95% for complex 3a) are unprecedented for bis-tridentate RuII polypyridyl complexes.This is attributed to the longlived excited state of the [Ru(dqp)2]2+ complex combined with fast electron transfer from the donor moiety following the initial charge separation. The rodlike arrangement of donor and acceptor gives controlled, vectorial electron transfer, free from the complications of stereoisomeric diversity. Thus, such arrays provide an excellent system for the study of photoinduced electron transfer and, ultimately, the harvesting of solar energy.

  • 32. Le Pleux, Loic
    et al.
    Smeigh, Amanda L.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science.
    Gibson, Elizabeth
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Physical and Analytical Chemistry.
    Pellegrin, Yann
    Blart, Errol
    Boschloo, Gerrit
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Physical and Analytical Chemistry.
    Hagfeldt, Anders
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Physical and Analytical Chemistry.
    Hammarström, Leif
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Chemical Physics.
    Odobel, Fabrice
    Synthesis, photophysical and photovoltaic investigations of acceptor-functionalized perylene monoimide dyes for nickel oxide p-type dye-sensitized solar cells2011In: ENERGY & ENVIRONMENTAL SCIENCE, ISSN 1754-5692, Vol. 4, no 6, p. 2075-2084Article in journal (Refereed)
    Abstract [en]

    We report on the synthesis, electrochemical, photophysical, and photovoltaic properties of a series of three organic dyads comprising a perylene monoimide (PMI) dye connected to a naphthalene diimide (NDI) or a fullerene (C-60) for application in dye-sensitized solar cells (DSCs) with nanocrystalline NiO electrodes. It was found that the secondary electron acceptor (NDI or C-60) in all the three dyads extends the charge separated state lifetime by about five orders of magnitude compared to the respective parent PMI dye. Nanosecond pump-probe experiments of the NiO/dyads in the presence of the electrolyte show that the reduction of triiodide by the secondary electron acceptor is slow in all the dyads, which we ascribe to a weak driving force for this reaction. This reaction is significantly faster with the cobalt electrolyte (tris(4,4'-di-tert-butyl-2,2'-bipyridine)cobalt(II/III)), whose driving force is larger; however, its reaction with the reduced dyads is still rather slow. We demonstrate that the larger photovoltage observed with the cobalt electrolyte (V-OC = 285 mV) relative to the iodide electrolyte (V-OC = 120 mV) is due to a decrease in the dark current for the former owing to slower interfacial electron transfer of the reduced mediator with the injected holes into the NiO electrode. In terms of photovoltaic performances, the most efficient dyad is the system in which the NDI is directly connected to the PMI (eta = 0.14% under AM 1.5 with the cobalt electrolyte), but the dyad containing the fullerene acceptor exhibits the highest IPCE and the highest short circuit current density (IPCE = 57%, J(SC) = 1.88 mA cm(-2)) with the iodide electrolyte. The latter performances are attributed to the slightly stronger reducing power of C-60 relative to NDI, which favours the reduction of the mediator in the electrolyte.

  • 33.
    Lignell, Martin
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Chemical Physics.
    Structural Transitions in Helical Peptides: The Influence of Water – Implications for Molecular Recognition and Protein Folding2009Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Fluctuations in protein structure are vital to function. This contrasts the dominating structure-function paradigm, which connects the well-defined three-dimensional protein structure to its function. However, catalysis is observed in disordered enzymes, which lack a defined structure. Disordered proteins are involved in molecular recognition events as well. The aim of this Thesis is to describe the structural changes occuring in protein structure and to investigate the mechanism of molecular recognition.

    Protein architecture is classified in a hierarchical manner, that is, it is categorized into primary, secondary, and tertiary levels. One of the major questions in biology today is how proteins fold into a defined three-dimensional structure. Some protein folding models, like the framework model, suggest that the secondary structure, like α-helices, is formed before the tertiary structure. This Thesis raises two questions: First, are structural fluctuations that occur in the protein related to the folding of the protein structure? Second, is the hierarchic classification of the protein architecture useful to describe said structural fluctuations?

    Kinetic studies of protein folding show that important dynamical processes of the folding occur on the microsecond timescale, which is why time-resolved fluorescence spectroscopy was chosen as the principal method for studying structural fluctuations in the peptides. Time-resolved fluorescence spectroscopy offers a number of experimental advantages and is useful for characterizing typical structural elements of the peptides on the sub-microsecond timescale. By observing the fluorescence lifetime distribution of the fluorescent probe, which is a part of the hydrophobic core of a four-helix bundle, it is shown that the hydrophobic core changes hydration state, from a completely dehydrated to a partly hydrated hydrophobic core. These fluctuations are related to the tertiary structure of the four-helix bundle and constitute structural transitions between the completely folded four-helix bundle and the molten globule version. Equilibrium unfolding of the four-helix bundle, using chemical denaturants or increased temperature, shows that the tertiary structure unfolds before the secondary structure, via the molten globule state, which suggests a hierarchic folding mechanism of the four-helix bundle.

    Fluctuations of a 12 amino acid long helical segment, without tertiary structure, involve a conformational search of different helical organizations of the backbone.

    Binding and recognition of a helix-loop-helix to carbonic anhydrase occurs through a partly folded intermediate before the final tertiary and bimolecular structure is formed between the two biomolecules. This confirms the latest established theory of recognition that the binding and the folding processes are coupled for the binding molecules.

    List of papers
    1. Conformational Switching Between 310, α and ∏-helical States in a 12 Amino Acid Long Peptide Studied by Time-resolved Fluorescence and CD Spectroscopy
    Open this publication in new window or tab >>Conformational Switching Between 310, α and ∏-helical States in a 12 Amino Acid Long Peptide Studied by Time-resolved Fluorescence and CD Spectroscopy
    (English)Article in journal (Refereed) In press
    Abstract [en]

    We have measured the end-to-end distance of a small peptide using time-resolved fluorescence energy transfer experiments and CD spectroscopy at various concentrations of TFE. The peptide comprises tryptophan as the donor and nitrotyrosine as the acceptor. The results show that the peptide is to a large degree helical even in the absence of TFE, and that addition of TFE to the solutions favors short, α-helical structures. Because of the nanosecond time resolution in the time-resolved fluorescence experiments, we are able to resolve four groups of donor–acceptor distances. The distances themselves do not change much with addition of TFE, however, the populations of the subgroups changes with TFE concentration. We assign the four resolvable distances to be, in decreasing length order, two forms of elongated, 310-helical structures, π-helical, and α-helical structures. The presence of multiple helical forms is supported by the fact that at least three components are needed to describe the change in CD upon addition of TFE. As we are observing the peptide under equilibrium conditions, the results tell that the peptide is at all TFE concentrations undergoing length changes, which are also accompanied by changes in hydration/solvent exposure. Addition of TFE does not appear to change the peptide structures, but changes the energy landscape in favor of short, α-helical structures.

    Keywords
    Time-resolved fluorescence spectroscopy, CD spectroscopy, conformational dynamics
    Identifiers
    urn:nbn:se:uu:diva-109392 (URN)
    Available from: 2009-10-14 Created: 2009-10-14 Last updated: 2010-01-14Bibliographically approved
    2. Sequential Equilibrium Unfolding of a Four-helix Bundle Peptide Shows that Urea and Guanidine have Different Effects on Tertiary and Secondary Structure. A CD and Time-resolved Fluorescence Spectroscopy Study
    Open this publication in new window or tab >>Sequential Equilibrium Unfolding of a Four-helix Bundle Peptide Shows that Urea and Guanidine have Different Effects on Tertiary and Secondary Structure. A CD and Time-resolved Fluorescence Spectroscopy Study
    (English)In: Biophysical Journal, ISSN 0006-3495, E-ISSN 1542-0086Article in journal (Refereed) Submitted
    Abstract [en]

    In this paper we show, using time-resolved fluorescence and CD spectroscopy, that equilibrium unfolding of the homodimeric four-helix bundle peptide (KE2D15)2 occurs via different pathways depending on the denaturant. The initial effect of guanidine hydrochloride (GdHCl) and urea is similar insofar that the tertiary structure is slightly destabilized. This is accompanied by a slight increase in helicity, which we believe is due to stabilization of the backbone at the expense of hydrophobic core stability. With GdHCl we observe an almost immediate (≥2 M GdHCl) dissociation of the dimer into helical monomers, while the effect of urea is to stabilize the helices and induce a solvent- or urea-separated state that persists up to about 5 M urea. At high urea concentrations, the peptide exists in monomeric but helical form. The partial and full dissociation of the dimeric four-helix bundle is monitored through time-resolved fluorescence spectroscopy. Through the use of time-resolved fluorescence, we can assess the heterogeneity of the partly and fully denatured states even though the denaturation is carried out at equilibrium conditions. The width of the fluorescence lifetime distributions are analyzed in terms of conformational space of the peptide.

    Keywords
    conformational dynamics, protein folding, chemical denaturants, time-resolved fluorescence spectroscopy, CD spectroscopy
    Identifiers
    urn:nbn:se:uu:diva-109375 (URN)
    Available from: 2009-10-14 Created: 2009-10-14 Last updated: 2017-12-12Bibliographically approved
    3. Recognition and binding of a helix-loop-helix peptide to carbonic anhydrase occurs via partly folded intermediate structures
    Open this publication in new window or tab >>Recognition and binding of a helix-loop-helix peptide to carbonic anhydrase occurs via partly folded intermediate structures
    2010 (English)In: Biophysical Journal, ISSN 0006-3495, E-ISSN 1542-0086, Vol. 98, no 3, p. 425-433Article in journal (Refereed) Published
    Abstract [en]

    We have studied the association of a fluorescently labeled helix–loop–helix peptide scaffold carrying a benzensulfonamide ligand to carbonic anhydrase using steady state and time-resolved fluorescence spectroscopy. The helix–loop–helix peptide, developed for biosensing applications, is labeled with the fluorescent probe dansyl, which serves as a polarity-sensitive reporter of the binding event. Using maximum entropy analysis of the fluorescence lifetime of the dansyl at 1:1 stoichiometry reveals three characteristic fluorescence lifetime groups, which are interpreted as differently interacting peptide–protein structures. We characterize these as mostly bound but unfolded, bound and partly folded, and strongly bound and folded peptide–protein complexes. Furthermore, analysis of the fluorescence anisotropy decay resulted in three different dansyl rotational correlation times, namely 0.18, 1.2, and 23 ns. Using their amplitudes, we can correlate the lifetime groups with the corresponding fluorescence lifetime group. The 23 ns rotational correlation time, which appears with the same amplitude as a 17 ns fluorescence lifetime, shows that the dansyl fluophorophore follows the rotational diffusion of carbonic anhydrase when it is a part of the folded peptide–protein complex. A partly folded and partly hydrated interfacial structure is manifested by a 8 ns dansyl fluorescence lifetime and a 1.2 ns rotational correlation time. This structure, we believe, is similar to a molten-globule-like interfacial structure which allows faster segmental movements and a higher degree of solvent exposure of dansyl. Excitation of dansyl on the helix–loop–helix peptide through Förster energy transfer from one or several tryptophans in the carbonic anhydrase, shows that the helix–loop–helix scaffold binds to a tryptophan-rich domain of the carbonic anhydrase. We conclude that the binding of the peptide to carbonic anhydrase involves a transition from a disordered to ordered structure of the helix–loop–helix scaffold.

    Keywords
    molecular recognition, protein dynamics, time-resolved fluorescence spectroscopy, disordered proteins, disordered to ordered structural transition
    National Category
    Chemical Sciences
    Identifiers
    urn:nbn:se:uu:diva-109373 (URN)10.1016/j.bpj.2009.10.038 (DOI)000274313200010 ()20141756 (PubMedID)
    Available from: 2009-10-14 Created: 2009-10-14 Last updated: 2017-12-12Bibliographically approved
    4. Hydrated and Dehydrated Tertiary Interactions - Opening and Closing - of a Four-helix Bundle Peptide
    Open this publication in new window or tab >>Hydrated and Dehydrated Tertiary Interactions - Opening and Closing - of a Four-helix Bundle Peptide
    2009 (English)In: Biophysical Journal, ISSN 0006-3495, E-ISSN 1542-0086, Vol. 97, no 2, p. 572-580Article in journal (Refereed) Published
    Abstract [en]

    The structural heterogeneity and thermal denaturation of a dansyl-labeled four-helix bundle homodimeric peptide has been studied with steady state and time-resolved fluorescence spectroscopy and with circular dichroism. At room temperature the fluorescence decay of the polarity-sensitive dansyl, located in the hydrophobic core region, can be described by a broad distribution of fluorescence lifetimes, reflecting the heterogeneous microenvironment. However, the lifetime distribution is nearly bimodal, which we ascribe to the presence of two major conformational subgroups. Since the fluorescence lifetime reflects the water content of the four-helix bundle conformations we can use the lifetime analysis to monitor the change of hydration state of the hydrophobic core of the four-helix bundle. Increasing the temperature from 9 °C to 23 °C leads to an increased population of molten-globule-like conformations with a less ordered helical backbone structure. The fluorescence emission maximum remains constant in this temperature interval, and the hydrophobic core is not strongly affected. Above 30 °C the structural dynamics involve transient openings of the four-helix bundle structure as evidenced by the emergence of a water-quenched component and less negative CD. Above 60 °C the homodimer starts to dissociate, as shown by the increasing loss of CD and narrow, short-lived fluorescence lifetime distributions.

    Place, publisher, year, edition, pages
    Elsevier, 2009
    Keywords
    time-resolved fluorescence spectroscopy, protein dynamics, CD-spectroscopy
    National Category
    Other Basic Medicine
    Identifiers
    urn:nbn:se:uu:diva-109369 (URN)10.1016/j.bpj.2009.04.055 (DOI)000268428700019 ()
    Available from: 2009-10-14 Created: 2009-10-14 Last updated: 2018-01-12Bibliographically approved
  • 34.
    Lignell, Martin
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Chemical Physics.
    Becker, Hans-Christian
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Chemical Physics.
    Conformational Switching Between 310, α and ∏-helical States in a 12 Amino Acid Long Peptide Studied by Time-resolved Fluorescence and CD SpectroscopyArticle in journal (Refereed)
    Abstract [en]

    We have measured the end-to-end distance of a small peptide using time-resolved fluorescence energy transfer experiments and CD spectroscopy at various concentrations of TFE. The peptide comprises tryptophan as the donor and nitrotyrosine as the acceptor. The results show that the peptide is to a large degree helical even in the absence of TFE, and that addition of TFE to the solutions favors short, α-helical structures. Because of the nanosecond time resolution in the time-resolved fluorescence experiments, we are able to resolve four groups of donor–acceptor distances. The distances themselves do not change much with addition of TFE, however, the populations of the subgroups changes with TFE concentration. We assign the four resolvable distances to be, in decreasing length order, two forms of elongated, 310-helical structures, π-helical, and α-helical structures. The presence of multiple helical forms is supported by the fact that at least three components are needed to describe the change in CD upon addition of TFE. As we are observing the peptide under equilibrium conditions, the results tell that the peptide is at all TFE concentrations undergoing length changes, which are also accompanied by changes in hydration/solvent exposure. Addition of TFE does not appear to change the peptide structures, but changes the energy landscape in favor of short, α-helical structures.

  • 35.
    Lignell, Martin
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Chemical Physics.
    Becker, Hans-Christian
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Chemical Physics.
    Recognition and binding of a helix-loop-helix peptide to carbonic anhydrase occurs via partly folded intermediate structures2010In: Biophysical Journal, ISSN 0006-3495, E-ISSN 1542-0086, Vol. 98, no 3, p. 425-433Article in journal (Refereed)
    Abstract [en]

    We have studied the association of a fluorescently labeled helix–loop–helix peptide scaffold carrying a benzensulfonamide ligand to carbonic anhydrase using steady state and time-resolved fluorescence spectroscopy. The helix–loop–helix peptide, developed for biosensing applications, is labeled with the fluorescent probe dansyl, which serves as a polarity-sensitive reporter of the binding event. Using maximum entropy analysis of the fluorescence lifetime of the dansyl at 1:1 stoichiometry reveals three characteristic fluorescence lifetime groups, which are interpreted as differently interacting peptide–protein structures. We characterize these as mostly bound but unfolded, bound and partly folded, and strongly bound and folded peptide–protein complexes. Furthermore, analysis of the fluorescence anisotropy decay resulted in three different dansyl rotational correlation times, namely 0.18, 1.2, and 23 ns. Using their amplitudes, we can correlate the lifetime groups with the corresponding fluorescence lifetime group. The 23 ns rotational correlation time, which appears with the same amplitude as a 17 ns fluorescence lifetime, shows that the dansyl fluophorophore follows the rotational diffusion of carbonic anhydrase when it is a part of the folded peptide–protein complex. A partly folded and partly hydrated interfacial structure is manifested by a 8 ns dansyl fluorescence lifetime and a 1.2 ns rotational correlation time. This structure, we believe, is similar to a molten-globule-like interfacial structure which allows faster segmental movements and a higher degree of solvent exposure of dansyl. Excitation of dansyl on the helix–loop–helix peptide through Förster energy transfer from one or several tryptophans in the carbonic anhydrase, shows that the helix–loop–helix scaffold binds to a tryptophan-rich domain of the carbonic anhydrase. We conclude that the binding of the peptide to carbonic anhydrase involves a transition from a disordered to ordered structure of the helix–loop–helix scaffold.

  • 36.
    Lignell, Martin
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Chemical Physics.
    Becker, Hans-Christian
    Sequential Equilibrium Unfolding of a Four-helix Bundle Peptide Shows that Urea and Guanidine have Different Effects on Tertiary and Secondary Structure. A CD and Time-resolved Fluorescence Spectroscopy StudyIn: Biophysical Journal, ISSN 0006-3495, E-ISSN 1542-0086Article in journal (Refereed)
    Abstract [en]

    In this paper we show, using time-resolved fluorescence and CD spectroscopy, that equilibrium unfolding of the homodimeric four-helix bundle peptide (KE2D15)2 occurs via different pathways depending on the denaturant. The initial effect of guanidine hydrochloride (GdHCl) and urea is similar insofar that the tertiary structure is slightly destabilized. This is accompanied by a slight increase in helicity, which we believe is due to stabilization of the backbone at the expense of hydrophobic core stability. With GdHCl we observe an almost immediate (≥2 M GdHCl) dissociation of the dimer into helical monomers, while the effect of urea is to stabilize the helices and induce a solvent- or urea-separated state that persists up to about 5 M urea. At high urea concentrations, the peptide exists in monomeric but helical form. The partial and full dissociation of the dimeric four-helix bundle is monitored through time-resolved fluorescence spectroscopy. Through the use of time-resolved fluorescence, we can assess the heterogeneity of the partly and fully denatured states even though the denaturation is carried out at equilibrium conditions. The width of the fluorescence lifetime distributions are analyzed in terms of conformational space of the peptide.

  • 37.
    Lignell, Martin
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Chemical Physics.
    Tegler, Lotta
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Biochemistry and Organic Chemistry.
    Becker, Hans-Christian
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Chemical Physics.
    Hydrated and Dehydrated Tertiary Interactions - Opening and Closing - of a Four-helix Bundle Peptide2009In: Biophysical Journal, ISSN 0006-3495, E-ISSN 1542-0086, Vol. 97, no 2, p. 572-580Article in journal (Refereed)
    Abstract [en]

    The structural heterogeneity and thermal denaturation of a dansyl-labeled four-helix bundle homodimeric peptide has been studied with steady state and time-resolved fluorescence spectroscopy and with circular dichroism. At room temperature the fluorescence decay of the polarity-sensitive dansyl, located in the hydrophobic core region, can be described by a broad distribution of fluorescence lifetimes, reflecting the heterogeneous microenvironment. However, the lifetime distribution is nearly bimodal, which we ascribe to the presence of two major conformational subgroups. Since the fluorescence lifetime reflects the water content of the four-helix bundle conformations we can use the lifetime analysis to monitor the change of hydration state of the hydrophobic core of the four-helix bundle. Increasing the temperature from 9 °C to 23 °C leads to an increased population of molten-globule-like conformations with a less ordered helical backbone structure. The fluorescence emission maximum remains constant in this temperature interval, and the hydrophobic core is not strongly affected. Above 30 °C the structural dynamics involve transient openings of the four-helix bundle structure as evidenced by the emergence of a water-quenched component and less negative CD. Above 60 °C the homodimer starts to dissociate, as shown by the increasing loss of CD and narrow, short-lived fluorescence lifetime distributions.

  • 38.
    Lissau, Jonas Sandby
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Chemical Physics.
    Gardner, James M.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Chemical Physics.
    Morandeira, Ana
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Chemical Physics.
    Photon Upconversion on Dye-Sensitized Nanostructured ZrO2 Films2011In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 115, no 46, p. 23226-23232Article in journal (Refereed)
    Abstract [en]

    Photon upconversion based on sensitized triplet triplet annihilation has been observed on nanocrystalline ZrO(2) films cosensitized with platinum(II) octaethylporphyrin (triplet sensitizer) and 9,10-diphenylanthracene (singlet emitter) under sunlight-like conditions (noncoherent excitation source, excitation light intensity as low as 5 mW/cm(2)). Time-resolved emission measurements showed a fast rise of the upconverted signal (<= 10 ns), suggesting that triplet energy migration most probably occurs through a "static" Dexter mechanism. To the best of our knowledge, this is the first observation of photon upconversion based on sensitized triplet triplet annihilation on a sensitized mesoporous metal oxide. Implementation of similar systems in dye-sensitized solar cells would increase the maximum theoretical efficiency of these devices from 30% to over 40%.

  • 39.
    Lomoth, Reiner
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Chemical Physics. Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Molecular Biomimetics.
    Magnuson, Ann
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Chemical Physics. Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Molecular Biomimetics.
    Sjödin, Martin
    Huang, Ping
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Chemical Physics. Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Molecular Biomimetics.
    Styring, Stenbjörn
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Chemical Physics. Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Molecular Biomimetics.
    Hammarström, Leif
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Chemical Physics. Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Molecular Biomimetics.
    Mimicking the electron donor side of Photosystem II in artificial photosynthesis.2006In: Photosynthesis Research, ISSN 0166-8595, E-ISSN 1573-5079, p. 1-16Article in journal (Refereed)
  • 40.
    Magnuson, Ann
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Physical Chemistry. Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Molecular Biomimetics. Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Chemical Physics. Avdelningen för molekylär biomimetik.
    Styring, Stenbjörn
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Molecular Biomimetics.
    Hammarström, L.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Physical Chemistry. Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Molecular Biomimetics. Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Chemical Physics.
    Understanding Photosystem II function by artificial photosynthesis2005In: Photosystem II: The Water/Plastoquinone Oxido-Reductase in Photosynthesis / [ed] Wydrzynski, T, Springer, Dordrecht, Netherlands , 2005, p. 753-775Chapter in book (Other academic)
  • 41. Monnereau, Cyrille
    et al.
    Gomez, Julio
    Blart, Errol
    Odobel, Fabrice
    Wallin, Staffan
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Chemistry, Department of Physical Chemistry. Physics, Department of Physics and Materials Science, Chemical Physics.
    Fallberg, Anna
    Hammarström, Leif
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Chemistry, Department of Physical Chemistry. Physics, Department of Physics and Materials Science, Chemical Physics.
    Photoinduced electron transfer in platinum(II) terpyridinyl acetylide complexes connected to a porphyrin unit.2005In: Inorg Chem, ISSN 0020-1669, Vol. 44, no 13, p. 4806-17Article in journal (Refereed)
  • 42.
    Ott, Sascha
    et al.
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Chemistry, Department of Photochemistry and Molecular Science. Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Chemistry, Department of Photochemistry and Molecular Science, Molecular Biomimetics. Physics, Department of Physics and Materials Science, Chemical Physics.
    Borgström, Magnus
    Hammarström, Leif
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Chemistry, Department of Photochemistry and Molecular Science. Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Chemistry, Department of Photochemistry and Molecular Science, Molecular Biomimetics. Physics, Department of Physics and Materials Science, Chemical Physics.
    Johansson, Olof
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Chemistry, Department of Photochemistry and Molecular Science. Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Chemistry, Department of Photochemistry and Molecular Science, Molecular Biomimetics. Physics, Department of Physics and Materials Science, Chemical Physics.
    Rapid energy transfer in bichromophoric tris-bipyridyl/cyclometallated ruthenium(II) complexes.2006In: Dalton Trans, ISSN 1477-9226, no 11, p. 1434-43Article in journal (Refereed)
  • 43.
    Petersson, Jonas
    et al.
    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.
    Davidsson, Jan
    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.
    Ultrafast Electron Transfer Dynamics of a Zn(II)porphyrin-Viologen Complex Revisited S-2 vs S-1 Reactions and Survival of Excess Excitation Energy2010In: Journal of Physical Chemistry B, ISSN 1520-6106, E-ISSN 1520-5207, Vol. 114, no 45, p. 14329-14338Article in journal (Refereed)
    Abstract [en]

    The photoinduced electron transfer reactions in a self-assembled 1 1 complex of zinc(II)tetrasulphonatophe nylporphyrin (ZnTPPS4-) and methylviologen (MV2+) in aqueous solution were investigated with transient absorption spectroscopy ZnTPPS4- was excited either in the Soret or one of the two Q-bands corresponding to excitation into the S-2 and S-1 states respectively The resulting electron transfer to MV2+ occurred surprisingly with the same time constant of tau(FET) = 180 fs from both electronic states The subsequent back electron transfer was rapid and the kinetics was independent of the initially excited state (tau(BET) = 700 fs) However ground state reactants in a set of vibrationally excited states were observed The amount of vibrationally excited ground states detected increased with increasing energy of the initial excited state showing that excess excitation energy survived a two-step electron transfer reaction in solution Differences in the ZnTPSS3-/MV+. spectra suggest that the forward election transfer from the S-2 state at least partially produces an electronically excited charge transfer state which effectively suppresses the influence of the inverted regime Other possible reasons for the similar election transfer rates for the different excited states are also discussed

  • 44. Planas, Nora
    et al.
    Vigara, Laura
    Cady, Clyde
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science.
    Miro, Pere
    Huang, Ping
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Molecular Biomimetics.
    Hammarström, Leif
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Chemical Physics.
    Styring, Stenbjorn
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Molecular Biomimetics.
    Leidel, Nils
    Dau, Holger
    Haumann, Michael
    Gagliardi, Laura
    Cramer, Christopher J.
    Llobet, Antoni
    Electronic Structure of Oxidized Complexes Derived from cis-Ru(II)(bpy)(2)(H(2)O)(2)](2+) and Its Photoisomerization Mechanism2011In: Inorganic Chemistry, ISSN 0020-1669, E-ISSN 1520-510X, Vol. 50, no 21, p. 11134-11142Article in journal (Refereed)
    Abstract [en]

    The geometry and electronic structure of cis-[Ru(II)(bpy)(2)(H(2)O)(2)](2+) and its higher oxidation state species up formally to Ru(VI) have been studied by means of UV-vis, EPR, XAS, and DFT and CASSCF/CASPT2 calculations. DFT calculations of the molecular structures of these species show that, as the oxidation state increases, the Ru-O bond distance decreases, indicating increased degrees of Ru-O multiple bonding. In addition, the O-Ru-O valence bond angle increases as the oxidation state increases. EPR spectroscopy and quantum chemical calculations indicate that low-spin configurations are favored for all oxidation states. Thus, cis-[Ru(IV)(bpy)(2)(OH)(0)](2+) (d(4)) has a singlet ground state and is EPR-silent at low temperatures, while cis-[Ru(V)(bpy)(2)(O)(OH)](2+) (d(3)) has a doublet ground state. XAS spectroscopy of higher oxidation state species and DFT calculations further illuminate the electronic structures of these complexes, particularly with respect to the covalent character of the O-Ru-O fragment. In addition, the photochemical isomerization of cis-[Ru(II)(bpy)(2)(H(2)O)(2)](2+) to its trans-[Ru(II)(bpy)(2)(H(2)O)(2)](2+) isomer has been fully characterized through quantum chemical calculations. The excited-state process is predicted to involve decoordination of one aqua ligand, which leads to a coordinatively unsaturated complex that undergoes structural rearrangement followed by recoordination of water to yield the trans isomer.

  • 45.
    Sascha, Ott
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Molecular Biomimetics.
    Stenbjörn, Styring
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Molecular Biomimetics.
    Hammarström, Leif
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Chemical Physics.
    Johansson, Olof
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Molecular Biomimetics.
    Towards Solar Fuels using a Biomimetic Approach: Progress in the Swedish Consortium for Artificial Photosyntesis2010In: Energy Production and Storage: Inorganic Chemical Strategies for a Warming World / [ed] Crabtree, R.H., Chichester, UK: Wiley , 2010Chapter in book (Other academic)
  • 46.
    Sjödin, Martin
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Chemical Physics.
    Irebo, Tania
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Chemical Physics.
    Utas, Josefin E.
    Lind, Johan
    Merenyi, Gabor
    Åkermark, Björn
    Hammarström, Leif
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Chemical Physics.
    Kinetic effects of hydrogen bonds on proton-coupled electron transfer from phenols2006In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 128, no 40, p. 13076-13083Article in journal (Refereed)
    Abstract [en]

    The kinetics and mechanism of proton-coupled electron transfer (PCET) from a series of phenols to a laser flash generated [Ru(bpy)(3)](3+) oxidant in aqueous solution was investigated. The reaction followed a concerted electron-proton transfer mechanism (CEP), both for the substituted phenols with an intramolecular hydrogen bond to a carboxylate group and for those where the proton was directly transferred to water. Without internal hydrogen bonds the concerted mechanism gave a characteristic pH-dependent rate for the phenol form that followed a Marcus free energy dependence, first reported for an intramolecular PCET in Sjodin, M. et al. J. Am. Chem. Soc. 2000, 122, 3932-3962 and now demonstrated also for a bimolecular oxidation of unsubstituted phenol. With internal hydrogen bonds instead, the rate was no longer pH-dependent, because the proton was transferred to the carboxylate base. The results suggest that while a concerted reaction has a relatively high reorganization energy (lambda), this may be significantly reduced by the hydrogen bonds, allowing for a lower barrier reaction path. It is further suggested that this is a general mechanism by which proton-coupled electron transfer in radical enzymes and model complexes may be promoted by hydrogen bonding. This is different from, and possibly in addition to, the generally suggested effect of hydrogen bonds on PCET in enhancing the proton vibrational wave function overlap between the reactant and donor states. In addition we demonstrate how the mechanism for phenol oxidation changes from a stepwise electron transfer-proton transfer with a stronger oxidant to a CEP with a weaker oxidant, for the same series of phenols. The hydrogen bonded CEP reaction may thus allow for a low energy barrier path that can operate efficiently at low driving forces, which is ideal for PCET reactions in biological systems.

  • 47.
    Sjödin, Martin
    et al.
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Chemistry, Department of Physical Chemistry. Physics, Department of Physics and Materials Science, Chemical Physics. Department of Photochemistry and Molecular Science, Molecular Biomimetics.
    Styring, Stenbjörn
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Chemistry, Department of Physical Chemistry. Physics, Department of Physics and Materials Science, Chemical Physics. Department of Photochemistry and Molecular Science, Molecular Biomimetics. Avdelningen för molekylär biomimetik.
    Wolpher, Henriette
    Xu, Yunhua
    Sun, Licheng
    Hammarström, Leif
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Chemistry, Department of Physical Chemistry. Physics, Department of Physics and Materials Science, Chemical Physics. Department of Photochemistry and Molecular Science, Molecular Biomimetics.
    Switching the redox mechanism: models for proton-coupled electron transfer from tyrosine and tryptophan.2005In: J Am Chem Soc, ISSN 0002-7863, Vol. 127, no 11, p. 3855-63Article in journal (Refereed)
  • 48.
    Streich, Daniel
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Chemical Physics.
    Astuti, Yeni
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Chemical Physics.
    Orlandi, Michele
    Schwartz, Lennart
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Molecular Biomimetics.
    Lomoth, Reiner
    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.
    Ott, Sascha
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Molecular Biomimetics.
    High-Turnover Photochemical Hydrogen Production Catalyzed by a Model Complex of the [FeFe]-Hydrogenase Active Site2010In: Chemistry - A European Journal, ISSN 0947-6539, E-ISSN 1521-3765, Vol. 16, no 1, p. 60-63Article in journal (Refereed)
  • 49.
    Streich, Daniel
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Chemical Physics.
    Karnahl, Michael
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Molecular Biomimetics.
    Astuti, Yeni
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science.
    Cady, Clyde W.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science.
    Hammarström, Leif
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Chemical Physics.
    Lomoth, Reiner
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Chemical Physics.
    Ott, Sascha
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Molecular Biomimetics.
    Comparing the Reactivity of Benzenedithiolate- versus Alkyldithiolate-Bridged Fe2(CO)6 Complexes with Competing Ligands2011In: European Journal of Inorganic Chemistry, ISSN 1434-1948, E-ISSN 1099-1948, no 7, p. 1106-1111Article in journal (Refereed)
    Abstract [en]

    The reactivity of [(mu-X(2)bdt)Fe-2(CO)(6)] [(bdt)1, X(2)bdt = 3,6-di-substituted bezenedithiolate; X = H, Cl] with ligands of different donor strengths is investigated and compared to that of [(mu-pdt)Fe-2(CO)(6)] [(pdt) 1, pdt = propyldithiolate] and [(mu-edt)Fe-2(CO)(6)] [(edt)1, edt = ethyldithiolate]. Strong donor ligands (L = CN-, PMe3) when added to (bdt) 1 lead to mononuclear [(bdt)Fe(L)(2)(CO)(2)], (bdt)6(L), in a disproportionation and fragmentation reaction, while simple ligand-substitution reactions occur on (edt)1 and (pdt)1 under identical conditions. In the presence of weaker ligands such as secondary amines or dmf, the alkyldithiolate-bridged complexes are unreactive, while (bdt)1 transforms to an O-2-sensitive, magnetically uncoupled species, potentially a mononuclear Fe-I complex coordinated by bdt and at least 2 CO ligands.

  • 50.
    Tschierlei, Stefanie
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Chemical Physics.
    Ott, Sascha
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Molecular Biomimetics.
    Lomoth, Reiner
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Chemical Physics.
    Spectroscopically characterized intermediates of catalytic H2 formation by [FeFe] hydrogenase models2011In: Energy & Environmental Science, ISSN 1754-5692, E-ISSN 1754-5706, Vol. 4, no 7, p. 2340-2352Article, review/survey (Refereed)
    Abstract [en]

    This review compiles species that are known or potential intermediates in the catalytic formation of H-2 by diiron dithiolate complexes inspired by the active site of the [FeFe] hydrogenases. The data collection emphasizes spectroscopic characteristics (NMR, IR, UV-Vis, EPR) of protonated and reduced derivatives of the iron complexes that could provide reference data to the identification of intermediates in mechanistic studies.

12 1 - 50 of 59
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