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  • 1.
    Ahmed, Md Estak
    et al.
    Indian Assoc Cultivat Sci, Sch Chem Sci, Kolkata 700032, India..
    Nayek, Abhijit
    Indian Assoc Cultivat Sci, Sch Chem Sci, Kolkata 700032, India..
    Krizan, Alenka
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström.
    Coutard, Nathan
    Univ Grenoble Alpes, Lab Chim & Biol Metaux, IRIG, CEA,CNRS, F-38000 Grenoble, France..
    Morozan, Adina
    Univ Grenoble Alpes, Lab Chim & Biol Metaux, IRIG, CEA,CNRS, F-38000 Grenoble, France..
    Dey, Somdatta Ghosh
    Indian Assoc Cultivat Sci, Sch Chem Sci, Kolkata 700032, India..
    Lomoth, Reiner
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Physical Chemistry.
    Hammarström, Leif
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Physical Chemistry.
    Artero, Vincent
    Univ Grenoble Alpes, Lab Chim & Biol Metaux, IRIG, CEA,CNRS, F-38000 Grenoble, France..
    Dey, Abhishek
    Indian Assoc Cultivat Sci, Sch Chem Sci, Kolkata 700032, India..
    A Bidirectional Bioinspired [FeFe]-Hydrogenase Model2022In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 144, no 8, p. 3614-3625Article in journal (Refereed)
    Abstract [en]

    With the price-competitiveness of solar and wind power, hydrogen technologies may be game changers for a cleaner, defossilized, and sustainable energy future. H-2 can indeed be produced in electrolyzers from water, stored for long periods, and converted back into power, on demand, in fuel cells. The feasibility of the latter process critically depends on the discovery of cheap and efficient catalysts able to replace platinum group metals at the anode and cathode of fuel cells. Bioinspiration can be key for designing such alternative catalysts. Here we show that a novel class of iron-based catalysts inspired from the active site of [FeFe]-hydrogenase behave as unprecedented bidirectional electrocatalysts for interconverting H-2 and protons efficiently under near-neutral aqueous conditions. Such bioinspired catalysts have been implemented at the anode of a functional membrane-less H-2/O-2 fuel cell device.

  • 2.
    Anderlund, Magnus F.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science.
    Högblom, Joakim
    Shi, Wei
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science.
    Huang, Ping
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science.
    Eriksson, Lars
    Weihe, Högni
    Styring, Stenbjörn
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science.
    Åkermark, Björn
    Lomoth, Reiner
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science.
    Magnuson, Ann
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science.
    Redox chemistry of a dimanganese(II,III) complex with an unsymmetric ligand: Water binding, deprotonation and accumulative light-induced oxidation2006In: European Journal of Inorganic Chemistry, ISSN 1434-1948, E-ISSN 1099-1948, no 24, p. 5033-5047Article in journal (Refereed)
    Abstract [en]

    A dinuclear manganese complex {[(Mn2L)-L-II,IIII(mu-OAc)(2)]-ClO4} has been synthesised, where L is the dianion of 2-{[bis-(pyrid-2-ylmethyl)amino]methyl}-6-{[(3,5-di-tert-butyl-2- hydroxybenzyl)(pyrid-2-ylmethyl)amino]methyl)-4-methylphenol, an unsymmetric binucleating ligand with two coordinating phenol groups. The two manganese ions, with a Mn-Mn distance of 3.498 angstrom, are bridged by the two bidentate acetate ligands and the 4-methylphenolate group of the ligand, resulting in a N3O3 and N2O4 donor set of Mn-II and Mn-II, respectively. Electrochemically [Mn2(II,III)L(mu-OAc)(2)](+) is reduced to [(Mn2L)-L-II,II(mu-OAc)(2)] at E-1/2(1)=-0.53 V versus Fc(+/0) and oxidised to [(Mn2L)-L-III,III(mu-OAC)(2)](2+) at E-1/2(2)=0.38 V versus Fc(+/0). All three redox states have been characterised by EPR, IR and UV/Vis spectroscopy. Subsequent oxidation of [(Mn2L)-L-II,III(mu-OAc)(2)](2+) [E-1/2(3)=0.75 V vs. Fc(+/0)] in dry acetonitrile results in an unstable primary product with a lifetime of about 100 ins. At high scan rates quasireversible voltammetric behaviour is found for all three electrode processes, with particularly slow electron transfer for the II,III/II,II [k(o)(1) = 0.002 cms(-1) and III,III/II,III [k(o)(2) = 0.005 cms(-1)] couples, which can be rationalised in terms of major distortions of the Mn-II centres. In aqueous media the bridging acetates are replaced by water-derived ligands. Deprotonation of these stabilises higher valence states, and photo-induced oxidation of the manganese complex results in a (Mn2L)-L-IlI,IV complex with oxo or hydroxo bridging ligands, which is further oxidised to an EPR-silent product. These results demonstrate that a larger number of metal-centred oxidations can be compressed in a narrow potential range if build up of charge is avoided by charge-compensating reactions.

  • 3.
    Arkhypchuk, Anna I.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - BMC, Physical Organic Chemistry.
    Mijangos, Edgar
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Molecular Biomimetics.
    Lomoth, Reiner
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Physical Chemistry.
    Ott, Sascha
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Molecular Biomimetics.
    Redox Switching in Ethenyl- Bridged Bisphospholes2014In: Chemistry - A European Journal, ISSN 0947-6539, E-ISSN 1521-3765, Vol. 20, no 49, p. 16083-16087Article in journal (Refereed)
    Abstract [en]

    A 2e(-)/2H(+) redox platform has been implemented in the ethenyl-bridged bisphosphol-3-ol 1 to afford the first phospholes that feature chemically reversible oxidations. Oxidation of the title compounds to the corresponding bisphosphol-3-one 2 leads to a change in conjugation topology and a concomitant hypsochromic shift of the lowest-energy absorption maximum by 100nm. Electrochemical oxidation proceeds without any detectable intermediates, whereas the deprotonated form of 1 can be observed in an aprotic medium during the reduction of 2. This dianionic intermediate 3 is characterized by end absorptions that are bathochromically shifted by circa 200nm compared to those of 2.

  • 4.
    Aster, Alexander
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström. Univ Geneva, Dept Phys Chem, 30 Quai Ernest Ansermet, CH-1211 Geneva, Switzerland.
    Wang, Shihuai
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Physical Chemistry.
    Mirmohades, Mohammad
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Physical Chemistry.
    Esmieu, Charlène
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Molecular Biomimetics. CNRS, LCC, 205 Route Narbonne,BP 44099, F-31077 Toulouse 4, France.
    Berggren, Gustav
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Molecular Biomimetics.
    Hammarström, Leif
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström.
    Lomoth, Reiner
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström.
    Metal vs. ligand protonation and the alleged proton-shuttling role of the azadithiolate ligand in catalytic H-2 formation with FeFe hydrogenase model complexes2019In: Chemical Science, ISSN 2041-6520, E-ISSN 2041-6539, Vol. 10, no 21, p. 5582-5588Article in journal (Refereed)
    Abstract [en]

    Electron and proton transfer reactions of diiron complexes [Fe(2)adt(CO)(6)] (1) and [Fe(2)adt(CO)(4)(PMe3)(2)] (4), with the biomimetic azadithiolate (adt) bridging ligand, have been investigated by real-time IR- and UV-vis-spectroscopic observation to elucidate the role of the adt-N as a potential proton shuttle in catalytic H-2 formation. Protonation of the one-electron reduced complex, 1(-), occurs on the adt-N yielding 1H and the same species is obtained by one-electron reduction of 1H(+). The preference for ligand vs. metal protonation in the Fe-2(i,0) state is presumably kinetic but no evidence for tautomerization of 1H to the hydride 1Hy was observed. This shows that the adt ligand does not work as a proton relay in the formation of hydride intermediates in the reduced catalyst. A hydride intermediate 1HHy(+) is formed only by protonation of 1H with stronger acid. Adt protonation results in reduction of the catalyst at much less negative potential, but subsequent protonation of the metal centers is not slowed down, as would be expected according to the decrease in basicity. Thus, the adtH(+) complex retains a high turnover frequency at the lowered overpotential. Instead of proton shuttling, we propose that this gain in catalytic performance compared to the propyldithiolate analogue might be rationalized in terms of lower reorganization energy for hydride formation with bulk acid upon adt protonation.

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  • 5.
    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.

  • 6.
    Borgström, Magnus
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Physical Chemistry.
    Johansson, Olof
    Lomoth, Reiner
    Berglund-Baudin, Helena
    Wallin, Staffan
    Sun, Licheng
    Åkermark, Björn
    Hammarström, Leif
    Electron Donor-Acceptor Dyads and Triads Based on Tris(bipyridine) Ruthenium(II) and Benzoquinone: Synthesis, Characterization, and Photoinduced Electron Transfer Reactions2003In: Inorganic Chemistry, ISSN 0020-1669, E-ISSN 1520-510X, Vol. 42, p. 5173-5184Article in journal (Refereed)
  • 7.
    Borgström, Magnus
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Physical Chemistry.
    Ott, Sascha
    Lomoth, Reiner
    Bergquist, Jonas
    Hammarström, Leif
    Johansson, Olof
    Femtosecond Pump-Pump-Probe Investigation of a Ru(II)-Ru(II)-Acceptor Triad: Attempts at Achieving High Energy Charge-Separated StatesManuscript (Other academic)
  • 8.
    Borgström, Magnus
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Physical and Analytical Chemistry. Fysikalisk kemi.
    Ott, Sascha
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science.
    Lomoth, Reiner
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science.
    Bergquist, Jonas
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Physical and Analytical Chemistry. Analytisk kemi.
    Hammarström, Leif
    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.
    Photoinduced energy transfer coupled to charge separation in a Ru(II)-Ru(II)-acceptor triad.2006In: Inorganic Chemistry, ISSN 0020-1669, E-ISSN 1520-510X, Vol. 45, no 12, p. 4820-4829Article in journal (Refereed)
  • 9. Canton, Sophie E.
    et al.
    Zhang, Xiaoyi
    Zhang, Jianxin
    van Driel, Tim B.
    Kjaer, Kasper S.
    Haldrup, Kristoffer
    Chabera, Pavel
    Harlang, Tobias
    Suarez-Alcantara, Karina
    Liu, Yizhu
    Perez, Jorge
    Bordage, Amelie
    Papai, Matyas
    Vanko, Gyoergy
    Jennings, Guy
    Kurtz, Charles A.
    Rovezzi, Mauro
    Glatzel, Pieter
    Smolentsev, Grigory
    Uhlig, Jens
    Dohn, Asmus O.
    Christensen, Morten
    Galler, Andreas
    Gawelda, Wojciech
    Bressler, Christian
    Lemke, Henrik T.
    Moller, Klaus B.
    Nielsen, Martin M.
    Lomoth, Reiner
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Physical Chemistry.
    Warnmark, Kenneth
    Sundstrom, Villy
    Toward Highlighting the Ultrafast Electron Transfer Dynamics at the Optically Dark Sites of Photocatalysts2013In: Journal of Physical Chemistry Letters, ISSN 1948-7185, E-ISSN 1948-7185, Vol. 4, no 11, p. 1972-1976Article in journal (Refereed)
    Abstract [en]

    Building a detailed understanding of the structure function relationship is a crucial step in the optimization of molecular photocatalysts employed in water splitting schemes. The optically dark nature of their active sites usually prevents a complete mapping of the photoinduced dynamics. In this work, transient X-ray absorption spectroscopy highlights the electronic and geometric changes that affect such a center in a bimetallic model complex. Upon selective excitation of the ruthenium chromophore, the cobalt moiety is reduced through intramolecular electron transfer and undergoes a spin flip accompanied by an average bond elongation of 0.20 +/- 0.03 angstrom. The analysis is supported by simulations based on density functional theory structures (B3LYP*/TZVP) and FEFF 9.0 multiple scattering calculations. More generally, these results exemplify the large potential of the technique for tracking elusive intermediates that impart unique functionalities in photochemical devices.

  • 10.
    Chabera, Pavel
    et al.
    Lund Univ, Dept Chem, Div Phys Chem, Box 124, SE-22100 Lund, Sweden..
    Kjaer, Kasper S.
    Lund Univ, Dept Chem, Div Phys Chem, Box 124, SE-22100 Lund, Sweden.;Stanford Univ, SLAC Natl Accelerator Lab, PULSE Inst, Menlo Pk, CA 94025 USA..
    Prakash, Om
    Lund Univ, Dept Chem, CAS, Box 124, SE-22100 Lund, Sweden..
    Honarfar, Alireza
    Lund Univ, Dept Chem, Div Phys Chem, Box 124, SE-22100 Lund, Sweden..
    Liu, Yizhu
    Lund Univ, Dept Chem, CAS, Box 124, SE-22100 Lund, Sweden..
    Fredin, Lisa A.
    Lund Univ, Dept Chem, Div Theoret Chem, Box 124, SE-22100 Lund, Sweden..
    Harlang, Tobias C. B.
    Lund Univ, Dept Chem, Div Phys Chem, Box 124, SE-22100 Lund, Sweden..
    Lidin, Sven
    Lund Univ, Dept Chem, CAS, Box 124, SE-22100 Lund, Sweden..
    Uhlig, Jens
    Lund Univ, Dept Chem, Div Phys Chem, Box 124, SE-22100 Lund, Sweden..
    Sundstrom, Villy
    Lund Univ, Dept Chem, Div Phys Chem, Box 124, SE-22100 Lund, Sweden..
    Lomoth, Reiner
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Physical Chemistry.
    Persson, Petter
    Lund Univ, Dept Chem, Div Theoret Chem, Box 124, SE-22100 Lund, Sweden..
    Warnmark, Kenneth
    Lund Univ, Dept Chem, CAS, Box 124, SE-22100 Lund, Sweden..
    Fe-II Hexa N-Heterocyclic Carbene Complex with a 528 ps Metal-to-Ligand Charge-Transfer Excited-State Lifetime2018In: Journal of Physical Chemistry Letters, ISSN 1948-7185, E-ISSN 1948-7185, Vol. 9, no 3, p. 459-463Article in journal (Refereed)
    Abstract [en]

    The iron carbene complex [Fe-II(btz)(3)](PF6)(2) (where btz = 3,3'-dimethyl-1,1'-bis(p-tolyl)-4,4'-bis(1,2,3-triazol-5-ylidene)) has been synthesized, isolated, and characterized as a low-spin ferrous complex. It exhibits strong metal-to-ligand charge transfer (MLCT) absorption bands throughout the visible spectrum, and excitation of these bands gives rise to a (MLCT)-M-3 state with a 528 ps excited-state lifetime in CH3CN solution that is more than one order of magnitude longer compared with the MLCT lifetime of any previously reported Fe-II complex. The low potential of the [Fe(btz)(3)](3+)/[Fe(btz)(3)](2+) redox couple makes the (MLCT)-M-3 state of [Fe-II(btz)(3)](2+) a potent photo-reductant that can be generated by light absorption throughout the visible spectrum. Taken together with our recent results on the [Fe-III(btz)(3)](3+) form of this complex, these results show that the Fe-II and Fe-III oxidation states of the same Fe(btz)(3) complex feature long-lived MLCT and LMCT states, respectively, demonstrating the versatility of iron N-heterocyclic carbene complexes as promising light-harvesters for a broad range of oxidizing and reducing conditions.

  • 11.
    Chabera, Pavel
    et al.
    Lund Univ, Dept Chem, Div Phys Chem, Box 124, SE-22100 Lund, Sweden..
    Liu, Yizhu
    Lund Univ, Dept Chem, CAS, Box 124, SE-22100 Lund, Sweden..
    Prakash, Om
    Lund Univ, Dept Chem, CAS, Box 124, SE-22100 Lund, Sweden..
    Thyrhaug, Erling
    Lund Univ, Dept Chem, Div Phys Chem, Box 124, SE-22100 Lund, Sweden..
    El Nahhas, Amal
    Lund Univ, Dept Chem, Div Phys Chem, Box 124, SE-22100 Lund, Sweden..
    Honarfar, Alireza
    Lund Univ, Dept Chem, Div Phys Chem, Box 124, SE-22100 Lund, Sweden..
    Essen, Sofia
    Lund Univ, Dept Chem, CAS, Box 124, SE-22100 Lund, Sweden..
    Fredin, Lisa A.
    Lund Univ, Dept Chem, Div Theoret Chem, Box 124, SE-22100 Lund, Sweden..
    Harlang, Tobias C. B.
    Lund Univ, Dept Chem, Div Phys Chem, Box 124, SE-22100 Lund, Sweden.;Tech Univ Denmark, Dept Phys, DK-2800 Lyngby, Denmark..
    Kjaer, Kasper S.
    Lund Univ, Dept Chem, Div Phys Chem, Box 124, SE-22100 Lund, Sweden.;Tech Univ Denmark, Dept Phys, DK-2800 Lyngby, Denmark..
    Handrup, Karsten
    Lund Univ, Dept Phys, Div Synchrotron Radiat Res, Box 118, SE-22100 Lund, Sweden..
    Ericson, Fredric
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Microsystems Technology.
    Tatsuno, Hideyuki
    Lund Univ, Dept Chem, Div Phys Chem, Box 124, SE-22100 Lund, Sweden..
    Morgan, Kelsey
    NIST, Boulder, CO 80305 USA..
    Schnadt, Joachim
    Lund Univ, Dept Phys, Div Synchrotron Radiat Res, Box 118, SE-22100 Lund, Sweden..
    Häggström, Lennart
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Physics.
    Ericsson, Tore
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Physics.
    Sobkowiak, Adam
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Lidin, Sven
    Lund Univ, Dept Chem, CAS, Box 124, SE-22100 Lund, Sweden..
    Huang, Ping
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Molecular Biomimetics.
    Styring, Stenbjörn
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Molecular Biomimetics.
    Uhlig, Jens
    Lund Univ, Dept Chem, Div Phys Chem, Box 124, SE-22100 Lund, Sweden..
    Bendix, Jesper
    Univ Copenhagen, Dept Chem, Univ Pk 5, DK-2100 Copenhagen, Denmark..
    Lomoth, Reiner
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Physical Chemistry.
    Sundström, Villy
    Lund Univ, Dept Chem, Div Phys Chem, Box 124, SE-22100 Lund, Sweden..
    Persson, Petter
    Lund Univ, Dept Chem, Div Theoret Chem, Box 124, SE-22100 Lund, Sweden..
    Warnmark, Kenneth
    Lund Univ, Dept Chem, CAS, Box 124, SE-22100 Lund, Sweden..
    A low-spin Fe(III) complex with 100-ps ligand-to-metal charge transfer photoluminescence2017In: Nature, ISSN 0028-0836, E-ISSN 1476-4687, Vol. 543, no 7647, p. 695-+Article in journal (Refereed)
    Abstract [en]

    Transition-metal complexes are used as photosensitizers(1), in light-emitting diodes, for biosensing and in photocatalysis(2). A key feature in these applications is excitation from the ground state to a charge-transfer state(3,4); the long charge-transfer-state lifetimes typical for complexes of ruthenium(5) and other precious metals are often essential to ensure high performance. There is much interest in replacing these scarce elements with Earth-abundant metals, with iron(6) and copper(7) being particularly attractive owing to their low cost and non-toxicity. But despite the exploration of innovative molecular designs(6,8-10), it remains a formidable scientific challenge(11) to access Earth-abundant transition-metal complexes with long-lived charge-transfer excited states. No known iron complexes are considered(12) photoluminescent at room temperature, and their rapid excited-state deactivation precludes their use as photosensitizers(13-15). Here we present the iron complex [Fe(btz)(3)](3+) (where btz is 3,3'-dimethyl-1,1'-bis(p-tolyl)-4,4'-bis(1,2,3-triazol-5-ylidene)), and show that the superior sigma-donor and pi-acceptor electron properties of the ligand stabilize the excited state sufficiently to realize a long charge-transfer lifetime of 100 picoseconds (ps) and room-temperature photoluminescence. This species is a low-spin Fe(III) d(5) complex, and emission occurs from a long-lived doublet ligand-to-metal charge-transfer ((LMCT)-L-2) state that is rarely seen for transition-metal complexes(4,16,17). The absence of intersystem crossing, which often gives rise to large excited-state energy losses in transition-metal complexes, enables the observation of spin-allowed emission directly to the ground state and could be exploited as an increased driving force in photochemical reactions on surfaces. These findings suggest that appropriate design strategies can deliver new iron-based materials for use as light emitters and photosensitizers.

  • 12.
    Eilers, Gerriet
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science.
    Schwartz, Lennart
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science.
    Stein, Matthias
    Zampella, Giuseppe
    de Gioia, Luca
    Ott, Sascha
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science.
    Lomoth, Reiner
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science.
    Ligand versus metal protonation of an iron hydrogenase active site mimic2007In: Chemistry - A European Journal, ISSN 0947-6539, E-ISSN 1521-3765, Vol. 13, no 25, p. 7075-7084Article in journal (Refereed)
    Abstract [en]

    The protonation behavior of the iron hydrogenase active-site mimic [Fe2(u-adt)(CO)4(PMe3)2] (1; adt=N-benzyl-azadithiolate) has been investigated by spectroscopic, electrochemical, and computational methods. The combination of an adt bridge and electron-donating phosphine ligands allows protonation of either the adt nitrogen to give [Fe2(μ-Hadt)(CO)4(PMe3)2]+ ([1H]+), the Fe-Fe bond to give [Fe2-(μ-adt)(μ-H)(CO)4(PMe3)2]+ ([1Hy]+), or both sites simultaneously to give [Fe2(μ-Hadt)(μ-H)(CO)4(PMe3)2]2+ ([1HHy]2+). Complex 1 and its protonation products have been characterized in acetonitrile solution by IR, 1H, and 31PNMR spectroscopy. The solution structures of all protonation states feature a basal/basal orientation of the phosphine ligands, which contrasts with the basal/apical structure of 1 in the solid state. Density functional calculations have been performed on all protonation states and a comparison between calculated and experimental spectra confirms the structural assignments. The ligand protonated complex [1H]+ (pKa =12) is the initial, metastable protonation product while the hydride [1Hy]+ (pKa=15) is the thermodynamically stable singly protonated form. Tautomerization of cation [1H]+ to [1Hy]+ does not occur spontaneously. However, it can be catalyzed by HCl (k=2.2M-1s-1), which results in the selective formation of cation [1Hy]+. The protonations of the two basic sites have strong mutual effects on their basicities such that the hydride (pKa=8) and the ammonium proton (pKa=5) of the doubly protonated cationic complex [1HHy]2+ are considerably more acidic than in the singly protonated analogues. The formation of dication [1HHy]2+ from cation [1H]+ is exceptionally slow with perchloric or trifluoromethanesulfonic acid (k= 0.15 M-1s-1), while the dication is formed substantially faster (k > 102 M-1 s-1) with hydrobromic acid. Electrochemically, 1 undergoes irreversible reduction at -2.2V versus ferrocene, and this potential shifts to -1.6, - 1.1, and -1.0 V for the cationic complexes [1H]+, [1Hy]+, and [1HHy]2+, respectively, upon protonation. The doubly protonated form [1HHy]2+ is reduced at less negative potential than all previously reported hydrogenase models, although catalytic proton reduction at this potential is characterized by slow turnover.

  • 13.
    Eilers, Gerriet
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry.
    Zettersten, Camilla
    Nyholm, Leif
    Hammarström, Leif
    Lomoth, Reiner
    Ligand exchange upon oxidation of a dinuclear Mn complex - Detection of structural changes by FT-IR spectroscopy and ESI-MS.2005In: Dalton Transactions, ISSN 1477-9226, E-ISSN 1477-9234, no 6, p. 1033-1041Article in journal (Refereed)
  • 14.
    Fredin, Lisa
    et al.
    NIST, Mat Measurement Lab, Chem Sci, Rockville, MD USA..
    Chabera, Pavel
    Lund Univ, Dept Chem, Chem Phys, Lund, Sweden..
    Lomoth, Reiner
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Physical Chemistry.
    Sundstrom, Villy
    Lund Univ, Lund, Sweden..
    Warnmark, Kenneth
    Lund Univ, Lund, Sweden..
    Persson, Petter
    Lund Univ, Theoret Chem, Lund, Sweden..
    Photochemistry of iron(III) carbenes2017In: Abstracts of Papers of the American Chemical Society, ISSN 0065-7727, Vol. 254Article in journal (Other academic)
  • 15. Fryxelius, Jacob
    et al.
    Eilers, Gerriet
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry.
    Feyziyev, Yashar
    Magnuson, Ann
    Sun, Licheng
    Lomoth, Reiner
    Synthesis and redox properties of a [meso-tris(4-nitrophenyl) corrolato]Mn(III) complex.2005In: Journal of Porphyrins and Phthalocyanines, ISSN 1088-4246, E-ISSN 1099-1409, no 9(6), p. 379-386Article in journal (Refereed)
  • 16.
    Hammarström, Leif
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Physical Chemistry.
    Brown, Allison
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström.
    Mirmohades, Mohammad
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Physical Chemistry.
    Pullen, Sonja
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Molecular Biomimetics.
    Ott, Sascha
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Molecular Biomimetics.
    Lomoth, Reiner
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Physical Chemistry.
    Mechanistic investigations and detection of intermediates of molecular proton reduction catalysts2014In: Abstracts of Papers of the American Chemical Society, ISSN 0065-7727, Vol. 247, article id 95-INORArticle in journal (Other academic)
  • 17.
    Hammarström, Leif
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström.
    Lomoth, Reiner
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström.
    Ott, Sascha
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström.
    Capturing intermediates of molecular solar fuels catalysts by time-resolved mid-IR spectroscopy2017In: Abstracts of Papers of the American Chemical Society, ISSN 0065-7727, Vol. 253Article in journal (Other academic)
  • 18.
    Harlang, Tobias C. B.
    et al.
    Lund Univ, Dept Chem Phys, SE-22100 Lund, Sweden..
    Liu, Yizhu
    Lund Univ, Dept Chem Phys, SE-22100 Lund, Sweden.;Lund Univ, Dept Chem, Ctr Anal & Synth, SE-22100 Lund, Sweden..
    Gordivska, Olga
    Lund Univ, Dept Chem, Ctr Anal & Synth, SE-22100 Lund, Sweden..
    Fredin, Lisa A.
    Lund Univ, Dept Chem, Theoret Chem Div, SE-22100 Lund, Sweden..
    Ponseca, Carlito S., Jr.
    Lund Univ, Dept Chem Phys, SE-22100 Lund, Sweden..
    Huang, Ping
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Molecular Biomimetics.
    Chabera, Pavel
    Lund Univ, Dept Chem Phys, SE-22100 Lund, Sweden..
    Kjaer, Kasper S.
    Lund Univ, Dept Chem Phys, SE-22100 Lund, Sweden.;Tech Univ Denmark, Dept Phys, DK-2800 Lyngby, Denmark..
    Mateos, Helena
    Lund Univ, Dept Chem Phys, SE-22100 Lund, Sweden..
    Uhlig, Jens
    Lund Univ, Dept Chem Phys, SE-22100 Lund, Sweden..
    Lomoth, Reiner
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Physical Chemistry.
    Wallenberg, Reine
    Lund Univ, nCHREM, SE-22100 Lund, Sweden..
    Styring, Stenbjörn
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Molecular Biomimetics.
    Persson, Petter
    Lund Univ, Dept Chem, Theoret Chem Div, SE-22100 Lund, Sweden..
    Sundstroem, Villy
    Lund Univ, Dept Chem Phys, SE-22100 Lund, Sweden..
    Waernmark, Kenneth
    Lund Univ, Dept Chem, Ctr Anal & Synth, SE-22100 Lund, Sweden..
    Iron sensitizer converts light to electrons with 92% yield2015In: Nature Chemistry, ISSN 1755-4330, E-ISSN 1755-4349, Vol. 7, no 11, p. 883-889Article in journal (Refereed)
    Abstract [en]

    Solar energy conversion in photovoltaics or photocatalysis involves light harvesting, or sensitization, of a semiconductor or catalyst as a first step. Rare elements are frequently used for this purpose, but they are obviously not ideal for large-scale implementation. Great efforts have been made to replace the widely used ruthenium with more abundant analogues like iron, but without much success due to the very short-lived excited states of the resulting iron complexes. Here, we describe the development of an iron-nitrogen-heterocyclic-carbene sensitizer with an excited-state lifetime that is nearly a thousand-fold longer than that of traditional iron polypyridyl complexes. By the use of electron paramagnetic resonance, transient absorption spectroscopy, transient terahertz spectroscopy and quantum chemical calculations, we show that the iron complex generates photoelectrons in the conduction band of titanium dioxide with a quantum yield of 92% from the 3MLCT (metal-to-ligand charge transfer) state. These results open up possibilities to develop solar energy-converting materials based on abundant elements.

  • 19.
    He, Jianjun
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Physical Chemistry.
    Benkö, Gábor
    Korodi, Ferenc
    Polívka, Tomás
    Lomoth, Reiner
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Physical Chemistry.
    Åkermark, Björn
    Sun, Licheng
    Hagfeldt, Anders
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Physical Chemistry.
    Sundström, Villy
    Modified Phtalocyanines for Efficient Near-IR Sensitization of Nanostructured TiO2 Electrode2002In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Journal of American Chemical Society, Vol. 124, p. 4922-4932Article in journal (Refereed)
  • 20.
    Huang, P.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Physical Chemistry.
    Magnusson, A.
    Lomoth, R.
    Abrahamsson, M.
    Tamm, M.
    Sun, L.
    van Rotterdam, B.
    Park, J.
    Hammarström, L.
    Åkermark, B.
    Styring, S.
    Photo-induced oxidation of a dinuclear Mn2II,II complex to the Mn2III, IV state by inter- and intramolecular electron transfer to RuIIItris-bipyridine2002In: Journal of Inorganic Biochemistry, ISSN 0162-0134, E-ISSN 1873-3344, Vol. 91, p. 159-172Article in journal (Refereed)
  • 21.
    Häupl, Tilmann
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Physical Chemistry.
    Lomoth, Reiner
    Hammarström, Leif
    Femtosecund Dynamics of the Photoexcited Methyl Viologen Radical Cation2003In: Journal of Physical Chemistry A, ISSN 1089-5639, E-ISSN 1520-5215, Vol. 107, no 4, p. 435-438Article in journal (Refereed)
  • 22.
    Ilic, Aleksandra
    et al.
    Lund Univ, Ctr Anal & Synth CAS, Dept Chem, SE-22100 Lund, Sweden..
    Schwarz, Jesper
    Lund Univ, Ctr Anal & Synth CAS, Dept Chem, SE-22100 Lund, Sweden..
    Johnson, Catherine
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Physical Chemistry.
    de Groot, Lisa H. M.
    Lund Univ, Ctr Anal & Synth CAS, Dept Chem, SE-22100 Lund, Sweden..
    Kaufhold, Simon
    Lund Univ, Ctr Anal & Synth CAS, Dept Chem, SE-22100 Lund, Sweden..
    Lomoth, Reiner
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Physical Chemistry.
    Warnmark, Kenneth
    Lund Univ, Ctr Anal & Synth CAS, Dept Chem, SE-22100 Lund, Sweden..
    Photoredox catalysis via consecutive 2LMCT- and 3MLCT-excitation of an Fe(iii/ii)–N-heterocyclic carbene complex2022In: Chemical Science, ISSN 2041-6520, E-ISSN 2041-6539, Vol. 13, no 32, p. 9165-9175Article in journal (Refereed)
    Abstract [en]

    Fe-N-heterocyclic carbene (NHC) complexes attract increasing attention as photosensitisers and photoredox catalysts. Such applications generally rely on sufficiently long excited state lifetimes and efficient bimolecular quenching, which leads to there being few examples of successful usage of Fe-NHC complexes to date. Here, we have employed [Fe(iii)(btz)(3)](3+) (btz = (3,3 '-dimethyl-1,1 '-bis(p-tolyl)-4,4 '-bis(1,2,3-triazol-5-ylidene))) in the addition of alkyl halides to alkenes and alkynes via visible light-mediated atom transfer radical addition (ATRA). Unlike other Fe-NHC complexes, [Fe(iii/ii)(btz)(3)](3+/2+) benefits from sizable charge transfer excited state lifetimes >= 0.1 ns in both oxidation states, and the Fe(iii) (LMCT)-L-2 and Fe(ii) (MLCT)-M-3 states are strong oxidants and reductants, respectively. The combined reactivity of both excited states enables efficient one-electron reduction of the alkyl halide substrate under green light irradiation. The two-photon mechanism proceeds via reductive quenching of the Fe(iii) (LMCT)-L-2 state by a sacrificial electron donor and subsequent excitation of the Fe(ii) product to its highly reducing (MLCT)-M-3 state. This route is shown to be more efficient than the alternative, where oxidative quenching of the less reducing Fe(iii) (LMCT)-L-2 state by the alkyl halide drives the reaction, in the absence of a sacrificial electron donor.

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  • 23.
    Jane, R. T.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Physical Chemistry.
    Gaudemer, E.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Physical Chemistry.
    Lomoth, Reiner
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Physical Chemistry.
    Surface modification of carbon and metal electrodes with bistable molecular redox switches by click and amide coupling2015In: Journal of Materials Chemistry C, ISSN 2050-7526, E-ISSN 2050-7534, Vol. 3, no 38, p. 10023-10030Article in journal (Refereed)
    Abstract [en]

    Ruthenium complexes [Ru(R-Ph-tpy)(bpyMeOHpy)] (Ph-tpy = 4'-(4-R-phenyl)-2,2':6',2 ''-terpyridine, R = NH2, COOH, CRCH, bpyMeOHpy = 1-[6-(2,2'-bipyridyl)]-1-(2-pyridyl)-ethanol) were covalently attached to carbon and metal electrodes by amide and click coupling reactions. Coupling agents were covalently grafted onto the electrodes by electrochemical reduction of p-functionalized diazonium tethers X-Ph-N-2(+) (X = COOH, NO2, N-3) followed by electrochemical reduction of the nitro tether. The modification of the electrode surfaces with the Ru complexes results in a hysteretic current-voltage response based on the redox-induced N-6/N5O linkage isomerism of the ambidentate pyridyl/alkoxy unit in the bpyMeOHpy chelate ligand. The immobilized complexes can be exhaustively addressed electrochemically with scan rates <= 10000 V s(-1) and can switch uniformly with kinetic and thermodynamic parameters similar to the properties of reference complexes in homogeneous solution.

  • 24.
    Jane, Reuben T.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Physical Chemistry.
    Lomoth, Reiner
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Physical Chemistry.
    Redox hysteresis on carbon electrodes covalently modified with a bistable ruthenium complex2015In: Journal of Materials Chemistry C, ISSN 2050-7526, E-ISSN 2050-7534, Vol. 3, no 24, p. 6260-6265Article in journal (Refereed)
    Abstract [en]

    A ruthenium complex bearing an ambidentate ligand was covalently attached to glassy carbon and carbon fiber electrodes by reduction of an aryldiazonium anchoring group placed on the terpyridine spectator ligand. The diazonium grafting method results in robust attachment and yields high surface concentrations of 2.4 x 10(-10) mol cm(-2). The attached complexes can be addressed electrochemically and the electrodes were characterized with scan rates of up to 2000 V s(-1). The redox-induced N/O linkage isomerism of the pyridyl/alkoxy ambidentate ligand results in a hysteretic current-voltage response (E-1 degrees = 0.83, E-2 degrees = 0.34 V) of the modified electrodes. The immobilization has no deleterious effects on the isomerization reactions of the molecular material that proceed with thermodynamic (2.4 < pK(1) < 3.7 (Ru(III) O -> N), -6.0 < pK(2) < -4.8 (Ru(II) O -> N)) and kinetic parameters (k(b1) = 2.5 x 10(2) s(-1) (Ru(III) N -> O), k(f2) = 2.5 x 10(2) s(-1) (Ru(II) O -> N)) comparable to analogous complexes in homogeneous solution.

  • 25. Johansson, Olof
    et al.
    Borgström, Magnus
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Physical Chemistry.
    Lomoth, Reiner
    Palmblad, Magnus
    Bergquist, Jonas
    Hammarström, Leif
    Sun, Licheng
    Åkermark, Björn
    Electron Donor-Acceptor Dyads Based on Ruthenium(II) Bipyridine and Terpyridine Complexes Bound to Naphtalenediimide2003In: Inorganic Chemistry, ISSN 0020-1669, E-ISSN 1520-510X, Vol. 42, p. 2908-2918Article in journal (Refereed)
  • 26.
    Johansson, Olof
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science.
    Eriksson, Lars
    Lomoth, Reiner
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science.
    Pd-catalyzed diarylation of aniline: a way to a non-linear bis(terpyridyl) ligand providing increased electronic communication2008In: Dalton Transactions, ISSN 1477-9226, E-ISSN 1477-9234, no 28, p. 3649-3651Article in journal (Refereed)
    Abstract [en]

    An amine-linked bis(terpyridyl) ligand, prepared via Pd-catalyzed diarylation of aniline, mediates unusually strong metal-metal interaction in its Ru-2 polypyridyl complex.

  • 27.
    Johansson, Olof
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science.
    Johannissen, Linus O.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science.
    Lomoth, Reiner
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science.
    Bistable Molecular Switches Based on Linkage Isomerization in Ruthenium Polypyridyl Complexes with a Ligand-Bound Ambidentate Motif2009In: Chemistry - A European Journal, ISSN 0947-6539, E-ISSN 1521-3765, Vol. 15, no 5, p. 1195-1204Article in journal (Refereed)
    Abstract [en]

    Electron-transfer-induced linkage isomerization was investigated in a series of bis-tridentate Ru polypyridyl complexes [Ru(L-X-OH)(Y-tpy)](2+) with ambidentate ligand L-X-OH bpy-C(R)(OH)-py (bpy-2,2'-bipyridine py-pyridine; R-H, Me, Ph, or tBu) and spectator ligand Y-tpy (tpy 2.2':6',2 ''-terpyridine, Y-p-tolyl, p-PhCO2Me, Cl, OEt, N-pyrrolidine). The ligand-bound ambidentate motif switches reversibly between N and O coordination in the Ru-II and Ru-III state,respectively. The potentials of the Ru-III/II couple differ by about 0.5 V between the isomers, and this results in a bistable electrochemical response of the molecular switches. The effects of structural modifications in form of substituents on the linking carbon atom of the ambidentate ligand and on the central pyridine moiety of the spectator ligand were investigated by electrochemical and computational methods. Differences in isomerization behavior span six orders of magnitude in rate constants and two orders of magnitude in equilibrium constants. The results can be interpreted in terms of steric and electronic substituent effects and their influence on rotational barriers, ligation geometry, and electron deficiency of the metal center.

  • 28.
    Johansson, Olof
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science.
    Lomoth, Reiner
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science.
    Molecular hysteresis in a rigid dinuclear ruthenium polypyridyl complex incorporating a ligand-bound ambidentate motif2008In: Inorganic Chemistry, ISSN 0020-1669, E-ISSN 1520-510X, Vol. 47, no 13, p. 5531-5533Article in journal (Refereed)
    Abstract [en]

    Two alternative Ru-2(2+/3+) mixed-valence states are formed in the first dinuclear Ru complex with a ligand-bound ambidentate motif. The hysteretic electrochemical response follows a double-square scheme where the structure of the mixed-valence state depends on the previous isovalent state. The Ru3+ state of the pyrrolidine-substituted bisterpyridine unit is characterized by intense ligand-to-metal charge-transfer absorptions that provide a distinctive signature of the corresponding mixed-valence state.

  • 29.
    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)
  • 30. Johansson, Olof
    et al.
    Wolpher, Henriette
    Borgström, Magnus
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Physical Chemistry.
    Lomoth, Reiner
    Hammarström, Leif
    Bergquist, Jonas
    Sun, Licheng
    Åkermark, Björn
    Intramolecular Charge Separation in a Hydrogen Bonded Tyrosine-Ruthenium(II)-Naphtalene Diimide Triad2004In: Chemical Communications, ISSN 1359-7345, E-ISSN 1364-548X, p. 194-195Article in journal (Refereed)
  • 31.
    Johnson, Catherine
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Physical Chemistry.
    Schwarz, Jesper
    Lund Univ, Dept Chem, Ctr Anal & Synth, Box 124, SE-22100 Lund, Sweden..
    Deegbey, Mawuli
    North Carolina State Univ, Dept Chem, Raleigh, NC 27695 USA..
    Prakash, Om
    Lund Univ, Dept Chem, Ctr Anal & Synth, Box 124, SE-22100 Lund, Sweden..
    Sharma, Kumkum
    Lund Univ, Dept Chem, Ctr Anal & Synth, Box 124, SE-22100 Lund, Sweden..
    Huang, Ping
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Molecular Biomimetics.
    Ericsson, Tore
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Physics.
    Häggström, Lennart
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy.
    Bendix, Jesper
    Univ Copenhagen, Dept Chem, Univ Pk 5, DK-2100 Copenhagen, Denmark..
    Gupta, Arvind Kumar
    Lund Univ, Dept Chem, Ctr Anal & Synth, Box 124, SE-22100 Lund, Sweden..
    Jakubikova, Elena
    North Carolina State Univ, Dept Chem, Raleigh, NC 27695 USA..
    Warnmark, Kenneth
    Lund Univ, Dept Chem, Ctr Anal & Synth, Box 124, SE-22100 Lund, Sweden..
    Lomoth, Reiner
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Physical Chemistry.
    Ferrous and ferric complexes with cyclometalating N-heterocyclic carbene ligands: a case of dual emission revisited2023In: Chemical Science, ISSN 2041-6520, E-ISSN 2041-6539, Vol. 14, no 37, p. 10129-10139Article in journal (Refereed)
    Abstract [en]

    Iron N-heterocyclic carbene (FeNHC) complexes with long-lived charge transfer states are emerging as a promising class of photoactive materials. We have synthesized [Fe-II(ImP)(2)] (ImP = bis(2,6-bis(3-methylimidazol-2-ylidene-1-yl)phenylene)) that combines carbene ligands with cyclometalation for additionally improved ligand field strength. The 9 ps lifetime of its (MLCT)-M-3 (metal-to-ligand charge transfer) state however reveals no benefit from cyclometalation compared to Fe(II) complexes with NHC/pyridine or pure NHC ligand sets. In acetonitrile solution, the Fe(II) complex forms a photoproduct that features emission characteristics (450 nm, 5.1 ns) that were previously attributed to a higher ((MLCT)-M-2) state of its Fe(III) analogue [Fe-III(ImP)(2)](+), which led to a claim of dual (MLCT and LMCT) emission. Revisiting the photophysics of [Fe-III(ImP)(2)](+), we confirmed however that higher ((MLCT)-M-2) states of [Fe-III(ImP)(2)](+) are short-lived (<10 ps) and therefore, in contrast to the previous interpretation, cannot give rise to emission on the nanosecond timescale. Accordingly, pristine [Fe-III(ImP)(2)](+) prepared by us only shows red emission from its lower (LMCT)-L-2 state (740 nm, 240 ps). The long-lived, higher energy emission previously reported for [Fe-III(ImP)(2)](+) is instead attributed to an impurity, most probably a photoproduct of the Fe(II) precursor. The previously reported emission quenching on the nanosecond time scale hence does not support any excited state reactivity of [Fe-III(ImP)(2)](+) itself.

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  • 32.
    Kaul, Nidhi
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Physical Chemistry.
    Lomoth, Reiner
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Physical Chemistry.
    The Carbene Cannibal: Photoinduced Symmetry-Breaking Charge Separation in an Fe(III) N-Heterocyclic Carbene2021In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 143, no 29, p. 10816-10821Article in journal (Refereed)
    Abstract [en]

    Photoinduced symmetry-breaking charge separation (SB-CS) processes offer the possibility of harvesting solar energy by electron transfer between identical molecules. Here, we present the first case of direct observation of bimolecular SB-CS in a transition metal complex, [(FeL2)-L-III](PF6) (L = [phenyl(tris(3-methylimidazol-1-ylidene))borate](-)). Photoexcitation of the complex in the visible region results in the formation of a doublet ligand-to-metal charge transfer ((LMCT)-L-2) excited state (E0-0 = 2.13 eV), which readily reacts with the doublet ground state to generate charge separated products, [(FeL2)-L-II] and [(FeL2)-L-IV](2+), with a measurable cage escape yield. Known spectral signatures allow for unambiguous identification of the products, whose formation and recombination are monitored with transient absorption spectroscopy. The unusual energetic landscape of [(FeL2)-L-III](+), as reflected in its ground and excited state reduction potentials, results in SB-CS being intrinsically exergonic (Delta G(CS)degrees similar to -0.7 eV). This is in contrast to most systems investigated in the literature, where Delta C-CS degrees is close to zero, and the charge transfer driven primarily by solvation effects. The study is therefore illustrative for the utilization of the rich redox chemistry accessible in transition metal complexes for the realization of SB-CS.

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  • 33.
    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.

  • 34.
    Kjmer, Kasper Skov
    et al.
    Lund Univ, Div Phys Chem, Dept Chem, Box 124, SE-22100 Lund, Sweden.
    Kaul, Nidhi
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Physical Chemistry.
    Prakash, Om
    Lund Univ, CAS, Dept Chem, Box 124, SE-22100 Lund, Sweden.
    Chabera, Pavel
    Lund Univ, Div Phys Chem, Dept Chem, Box 124, SE-22100 Lund, Sweden.
    Rosemann, Nils W.
    Lund Univ, Div Phys Chem, Dept Chem, Box 124, SE-22100 Lund, Sweden.
    Honarfar, Alireza
    Lund Univ, Div Phys Chem, Dept Chem, Box 124, SE-22100 Lund, Sweden.
    Gordivska, Olga
    Lund Univ, CAS, Dept Chem, Box 124, SE-22100 Lund, Sweden.
    Fredin, Lisa A.
    Lund Univ, Div Theoret Chem, Dept Chem, Box 124, SE-22100 Lund, Sweden;Lehigh Univ, Dept Chem, 6 E Packer Ave, Bethlehem, PA 18015 USA.
    Bergquist, Karl-Erik
    Lund Univ, CAS, Dept Chem, Box 124, SE-22100 Lund, Sweden.
    Häggström, Lennart
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Physics.
    Ericsson, Tore
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Physics.
    Lindh, Linnea
    Lund Univ, Div Phys Chem, Dept Chem, Box 124, SE-22100 Lund, Sweden.
    Yartsev, Arkady
    Lund Univ, Div Phys Chem, Dept Chem, Box 124, SE-22100 Lund, Sweden.
    Styring, Stenbjörn
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Molecular Biomimetics.
    Huang, Ping
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Molecular Biomimetics.
    Uhlug, Jens
    Lund Univ, Div Phys Chem, Dept Chem, Box 124, SE-22100 Lund, Sweden.
    Bendix, Jesper
    Univ Copenhagen, Dept Chem, Univ Pk 5, DK-2100 Copenhagen, Denmark.
    Strand, Daniel
    Lund Univ, CAS, Dept Chem, Box 124, SE-22100 Lund, Sweden.
    Sundström, Villy
    Lund Univ, Div Phys Chem, Dept Chem, Box 124, SE-22100 Lund, Sweden.
    Persson, Petter
    Lund Univ, Div Theoret Chem, Dept Chem, Box 124, SE-22100 Lund, Sweden.
    Lomoth, Reiner
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Physical Chemistry.
    Wärnmark, Kenneth
    Lund Univ, CAS, Dept Chem, Box 124, SE-22100 Lund, Sweden.
    Luminescence and reactivity of a charge-transfer excited iron complex with nanosecond lifetime2019In: Science, ISSN 0036-8075, E-ISSN 1095-9203, Vol. 363, no 6424, p. 249-253Article in journal (Refereed)
    Abstract [en]

    Iron's abundance and rich coordination chemistry are potentially appealing features for photochemical applications. However, the photoexcitable charge-transfer states of most iron complexes are limited by picosecond or subpicosecond deactivation through low-lying metal-centered states, resulting in inefficient electron-transfer reactivity and complete lack of photoluminescence. In this study, we show that octahedral coordination of iron(Ill) by two mono-anionic facial tris-carbene ligands can markedly suppress such deactivation. The resulting complex [Fe(phtmeimb)(2)](+), where phtmeimb is {phenyl[tris(3-methylimidazol-1-ylidene)]borate}(-), exhibits strong, visible, room temperature photoluminescence with a 2.0-nanosecond lifetime and 2% quantum yield via spin-allowed transition from a doublet ligand-to-metal charge-transfer ((LMCT)-L-2) state to the doublet ground state. Reductive and oxidative electron-transfer reactions were observed for the (2)LMCTstate of [Fe(phtmeimb)(2)](+) in bimolecular quenching studies with methylviologen and diphenylamine.

  • 35.
    Lei, Pengxiang
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science.
    Hedlund, Maria
    Lomoth, Reiner
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science.
    Rensmo, Håkan
    Johansson, Olof
    Hammarström, Leif
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science.
    The role of colloid formation in the photoinduced H2 production with a RuII-PdII supramolecular complex: A study by GC, XPS, and TEM2008In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 130, no 1, p. 26-27Article in journal (Refereed)
    Abstract [en]

    The dinuclear Run(II)-Pd-II complex shows efficient H-2 production in the presence of triethylamine as a sacrificial electron and proton donor under visible light irradiation. XPS and TEM analyses reveal that photoreduction of Pd-II to Pd-0 causes dissociation of Pd from the complex to form colloids that are suggested to be the actual catalyst for H-2 production.

  • 36.
    Lindh, Linnea
    et al.
    Lund Univ, Dept Chem, Chem Phys Div, Box 124, SE-22100 Lund, Sweden.;Lund Univ, Dept Chem, Theoret Chem Div, Box 124, SE-22100 Lund, Sweden..
    Gordivska, Olga
    Lund Univ, Ctr Anal & Synth, Dept Chem, Box 124, SE-22100 Lund, Sweden..
    Persson, Samuel
    Lund Univ, Ctr Anal & Synth, Dept Chem, Box 124, SE-22100 Lund, Sweden..
    Michaels, Hannes
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Physical Chemistry. Uppsala Univ, Dept Chem, Angstrom Lab, Box 523, SE-75120 Uppsala, Sweden.;Newcastle Univ, Sch Nat & Environm Sci, Bedson Bldg, Newcastle Upon Tyne NE1 7RU, Tyne & Wear, England..
    Fan, Hao
    Lund Univ, Ctr Anal & Synth, Dept Chem, Box 124, SE-22100 Lund, Sweden..
    Chabera, Pavel
    Lund Univ, Dept Chem, Chem Phys Div, Box 124, SE-22100 Lund, Sweden..
    Rosemann, Nils W.
    Lund Univ, Dept Chem, Chem Phys Div, Box 124, SE-22100 Lund, Sweden.;Lund Univ, Ctr Anal & Synth, Dept Chem, Box 124, SE-22100 Lund, Sweden..
    Gupta, Arvind Kumar
    Lund Univ, Ctr Anal & Synth, Dept Chem, Box 124, SE-22100 Lund, Sweden..
    Benesperi, Iacopo
    Lund Univ, Ctr Anal & Synth, Dept Chem, Box 124, SE-22100 Lund, Sweden.;Newcastle Univ, Sch Nat & Environm Sci, Bedson Bldg, Newcastle Upon Tyne NE1 7RU, Tyne & Wear, England..
    Uhlig, Jens
    Lund Univ, Dept Chem, Chem Phys Div, Box 124, SE-22100 Lund, Sweden..
    Prakash, Om
    Lund Univ, Ctr Anal & Synth, Dept Chem, Box 124, SE-22100 Lund, Sweden..
    Sheibani, Esmaeil
    Lund Univ, Ctr Anal & Synth, Dept Chem, Box 124, SE-22100 Lund, Sweden..
    Kjaer, Kasper S.
    Lund Univ, Dept Chem, Chem Phys Div, Box 124, SE-22100 Lund, Sweden..
    Boschloo, Gerrit
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Physical Chemistry.
    Yartsev, Arkady
    Lund Univ, Dept Chem, Chem Phys Div, Box 124, SE-22100 Lund, Sweden..
    Freitag, Marina
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Physical Chemistry. Newcastle Univ, Sch Nat & Environm Sci, Bedson Bldg, Newcastle Upon Tyne NE1 7RU, Tyne & Wear, England..
    Lomoth, Reiner
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Physical Chemistry.
    Persson, Petter
    Theoretical Chemistry Division, Department of Chemistry, Lund University, Box 124, SE-22100 Lund, Sweden .
    Warnmark, Kenneth
    Lund Univ, Ctr Anal & Synth, Dept Chem, Box 124, SE-22100 Lund, Sweden..
    Dye-sensitized solar cells based on Fe N-heterocyclic carbene photosensitizers with improved rod-like push-pull functionality2021In: Chemical Science, ISSN 2041-6520, E-ISSN 2041-6539, Vol. 12, no 48, p. 16035-16053Article in journal (Refereed)
    Abstract [en]

    A new generation of octahedral iron(ii)-N-heterocyclic carbene (NHC) complexes, employing different tridentate C<^>N<^>C ligands, has been designed and synthesized as earth-abundant photosensitizers for dye sensitized solar cells (DSSCs) and related solar energy conversion applications. This work introduces a linearly aligned push-pull design principle that reaches from the ligand having nitrogen-based electron donors, over the Fe(ii) centre, to the ligand having an electron withdrawing carboxylic acid anchor group. A combination of spectroscopy, electrochemistry, and quantum chemical calculations demonstrate the improved molecular excited state properties in terms of a broader absorption spectrum compared to the reference complex, as well as directional charge-transfer displacement of the lowest excited state towards the semiconductor substrate in accordance with the push-pull design. Prototype DSSCs based on one of the new Fe NHC photosensitizers demonstrate a power conversion efficiency exceeding 1% already for a basic DSSC set-up using only the I-/I-3(-) redox mediator and standard operating conditions, outcompeting the corresponding DSSC based on the homoleptic reference complex. Transient photovoltage measurements confirmed that adding the co-sensitizer chenodeoxycholic acid helped in improving the efficiency by increasing the electron lifetime in TiO2. Time-resolved spectroscopy revealed spectral signatures for successful ultrafast (<100 fs) interfacial electron injection from the heteroleptic dyes to TiO2. However, an ultrafast recombination process results in undesirable fast charge recombination from TiO2 back to the oxidized dye, leaving only 5-10% of the initially excited dyes available to contribute to a current in the DSSC. On slower timescales, time-resolved spectroscopy also found that the recombination dynamics (longer than 40 mu s) were significantly slower than the regeneration of the oxidized dye by the redox mediator (6-8 mu s). Therefore it is the ultrafast recombination down to fs-timescales, between the oxidized dye and the injected electron, that remains as one of the main bottlenecks to be targeted for achieving further improved solar energy conversion efficiencies in future work.

  • 37.
    Liu, Tianfei
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Physical Chemistry.
    Guo, Meiyuan
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Theoretical Chemistry.
    Orthaber, Andreas
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Molecular Biomimetics.
    Lomoth, Reiner
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Physical Chemistry.
    Lundberg, Marcus
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Theoretical Chemistry.
    Ott, Sascha
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Molecular Biomimetics.
    Hammarström, Leif
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Physical Chemistry.
    Accelerating proton-coupled electron transfer of metal hydrides in catalyst model reactions2018In: Nature Chemistry, ISSN 1755-4330, E-ISSN 1755-4349, Vol. 10, no 8, p. 881-887Article in journal (Refereed)
    Abstract [en]

    Metal hydrides are key intermediates in catalytic proton reduction and dihydrogen oxidation. There is currently much interest in appending proton relays near the metal centre to accelerate catalysis by proton-coupled electron transfer (PCET). However, the elementary PCET steps and the role of the proton relays are still poorly understood, and direct kinetic studies of these processes are scarce. Here, we report a series of tungsten hydride complexes as proxy catalysts, with covalently attached pyridyl groups as proton acceptors. The rate of their PCET reaction with external oxidants is increased by several orders of magnitude compared to that of the analogous systems with external pyridine on account of facilitated proton transfer. Moreover, the mechanism of the PCET reaction is altered by the appended bases. A unique feature is that the reaction can be tuned to follow three distinct PCET mechanisms-electron-first, proton-first or a concerted reaction-with very different sensitivities to oxidant and base strength. Such knowledge is crucial for rational improvements of solar fuel catalysts.

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  • 38. Liu, Yizhu
    et al.
    Harlang, Tobias
    Canton, Sophie E.
    Chabera, Pavel
    Suarez-Alcantara, Karina
    Fleckhaus, Andre
    Vithanage, Dimali A.
    Göransson, Erik
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Physical Chemistry.
    Corani, Alice
    Lomoth, Reiner
    Sundstrom, Villy
    Warnmark, Kenneth
    Towards longer-lived metal-to-ligand charge transfer states of iron(II) complexes: an N-heterocyclic carbene approach2013In: Chemical Communications, ISSN 1359-7345, E-ISSN 1364-548X, Vol. 49, no 57, p. 6412-6414Article in journal (Refereed)
    Abstract [en]

    A 9 ps (MLCT)-M-3 lifetime was achieved by a Fe-II complex based on C(NHC)<^>N(py)<^>C(NHC) pincer ligands. This is the longest known so far for any kind of complexes of this abundant metal, and increased by almost two orders of magnitude compared to the reference Fe-II bis-terpyridine complex.

  • 39. Liu, Yizhu
    et al.
    Kjær, Kasper S.
    Fredin, Lisa A.
    Chábera, Pavel
    Harlang, Tobias
    Canton, Sophie E.
    Lidin, Sven
    Zhang, Jianxin
    Lomoth, Reiner
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Physical Chemistry.
    Bergquist, Karl-Erik
    Persson, Petter
    Wärnmark, Kenneth
    Sundström, Villy
    A Heteroleptic Ferrous Complex with Mesoionic Bis(1,2,3-triazol-5-ylidene) Ligands: Taming the MLCT Excited State of Iron(II)2015In: Chemistry - A European Journal, ISSN 0947-6539, E-ISSN 1521-3765, Vol. 21, no 9, p. 3628-3639Article in journal (Refereed)
  • 40.
    Lomoth, R
    et al.
    University of Leipzig.
    Brede, O
    Spectral and kinetic identification of radical cations of pyrimidine bases by stepwise electron transfer1998In: Chemical Physics Letters, ISSN 0009-2614, E-ISSN 1873-4448, Vol. 288, no 1, p. 47-51Article in journal (Refereed)
    Abstract [en]

    Radical cations of methylated derivatives of uracil and thymine were generated by electron transfer to the parent radical cation, generated in acetone by nanosecond pulse radiolysis. The resulting transient absorption peaking around 400 and 550 nm is assigned to the radical cations of the pyrimidine bases. Direct kinetic and spectroscopic evidence for this assignment has been given by a subsequent electron transfer from triphenylamine to the pyrimidine radical cations yielding the characteristic absorption spectrum of the triphenylamine radical cation. (C) 1998 Elsevier Science B.V. All rights reserved.

  • 41.
    Lomoth, R
    et al.
    University of Leipzig.
    Naumov, S
    Brede, O
    Genuine pyrimidine radical cations generated by radiation-induced electron transfer to butyl chloride or acetone parent ions1999In: Journal of Physical Chemistry A, ISSN 1089-5639, E-ISSN 1520-5215, Vol. 103, no 15, p. 2641-2648Article in journal (Refereed)
    Abstract [en]

    Radical cations of multiple methylated uracils and thymines were generated by electron transfer to parent ions of solvents of low polarity such as n-butyl chloride and acetone. Pulse radiolysis resulted in the transient optical absorption spectra of the pyrimidine radical cations (Py.+) which exhibit bands generally peaking around lambda = 400 nm and in acetone showing an additional band in the range of lambda(max) = 500-560 nm. The identification of the solute radical cations is based on the direct observation of the formation of Py.+ by electron transfer (k = (1-2) x 10(10) M(-1)s(-1)), the nucleophilic reaction with the counterion (e.g., Cl-), the relatively low reactivity with oxygen even for the fully methylated nitrogen groups (k < 2 x 10(8) M(-1)s(-1)), and the observation of a subsequent electron transfer from triphenylamine to the pyrimidine radical cations proceeding in a diffusion-controlled manner. The solvent dependence of the spectral shape of Py.+ was also studied in acetone/n-butyl chloride mixtures and was found to depend on the polarity of the surroundings. This phenomenon is explained in terms of a lactam-lactim-like tautomerism of the transient involving the whole plane molecule. Quantum chemical calculations support the experimental findings by explaining the spectral structure and enable the formulation of the lactims as either 1,4- or 3,4-localized.

  • 42.
    Lomoth, R
    et al.
    University of Leipzig.
    Naumov, S
    Brede, O
    Transients of the oxidation of pyrimidines with SO4•-: Structure and reactivity of the resulting radicals1999In: Journal of Physical Chemistry A, ISSN 1089-5639, E-ISSN 1520-5215, Vol. 103, no 33, p. 6571-6579Article in journal (Refereed)
    Abstract [en]

    Depending on the methylation pattern, the reaction of SO4.- with various methylated pyrimidines yields radicals deprotonated at N(1) and C(5)-OH or C(6)-OH adduct radicals and probably allyl radicals by subsequent deprotonation at the C(5)-methyl group of the thymines. All of these radicals are derived from the initial SO4.- adducts on the pyrimidines that have lifetimes of several microseconds in the case of N(1)-methylated thymines. These transients could be taken for long lived pyrimidine radical cations. However, spectral and kinetic comparison with the pyrimidine radical cations generated by electron transfer in nonpolar solvents (butyl chloride, acetone) reveals the adduct nature of these transients. In the course of sulfate adduct decay, pyrimidine radical cations could be formed as nondetectable short-lived (tau < 20ns) intermediates rapidly reacting to the above-mentioned radical products. The reactivity of the SO4.- adducts, as well as that of the other pyrimidinyl radicals observed, was characterized by the subsequent oxidation of triphenylamine and di- or trimethoxybenzene, which supports the mechanistic interpretation given above. Hence there is no indication of long-lived pyrimidine radical cations under the conditions of the SO4.- oxidation of pyrimidines in aqueous solution.

  • 43.
    Lomoth, Reiner
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Physical Chemistry.
    Redox-Stimulated Motion and Bistability in Metal Complexes and Organometallic Compounds2013In: Antioxidants and Redox Signaling, ISSN 1523-0864, E-ISSN 1557-7716, Vol. 19, no 15, p. 1803-1814Article, review/survey (Refereed)
    Abstract [en]

    Significance: Control over reversible changes to molecular structure forms the basis for artificial molecular machines that could eventually lead to the development of molecule-based nanotechnology. Recent Advances: Particular applications in information storage and processing could emerge where the structural rearrangements give rise to bistability and molecular hysteresis effects. Critical Issues: Oxidation-state-dependent coordination and bonding preferences in transition metal complexes and organometallic compounds provide a versatile approach to the control of molecular motions by redox input, but so far, few structural motifs have been applied in redox-actuated molecular machines. Future Directions: Further progress toward molecule-based nanoscale devices might be accomplished with molecular components derived from a wider range of structural themes and forms of molecular motion. Examples of redox-stimulated rearrangements in metal complexes and organometallic compounds are described that have been employed in molecular machines or could be considered for the design of new functional molecules.

  • 44.
    Lomoth, Reiner
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Physical Chemistry.
    Huang, Ping
    Zheng, Jiutian
    Sun, Licheng
    Hammarström, Leif
    Åkermark, Björn
    Styring, Stenbjörn
    Synthesis and Characterization of a Dinuclear Manganese(III,III) Complex with Three Phenolate Ligands2002In: European Journal of Inorganic Chemistry, ISSN 1434-1948, E-ISSN 1099-1948, p. 2965-2974Article in journal (Refereed)
  • 45.
    Lomoth, Reiner
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Physical Chemistry.
    Häupl, Tilmann
    Johansson, Olof
    Hammarström, Leif
    Redox-Switchable Direction of Photoinduced Electron Transfer in an Ru(bpy)3+2-Viologen Dyad2002In: Chemistry - A European Journal, ISSN 0947-6539, E-ISSN 1521-3765, Vol. 8, no 1, p. 102-110Article in journal (Refereed)
  • 46.
    Lomoth, Reiner
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Physical Chemistry.
    Liu, Tianfei
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Physical Chemistry.
    Wang, Shihuai
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Physical Chemistry.
    Ott, Sascha
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Molecular Biomimetics.
    Hammarström, Leif
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Physical Chemistry.
    Probing the elementary steps of PCET catalysis2018In: Abstracts of Papers of the American Chemical Society, ISSN 0065-7727, Vol. 255Article in journal (Other academic)
  • 47.
    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)
  • 48.
    Lomoth, Reiner
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Physical Chemistry.
    Magnuson, Ann
    Xu, Yunhua
    Sun, Licheng
    Mixed-Valance Properties of an Acetate-Bridged Dinuclear Ruthenium (II,II) Complex2003In: Journal of Physical Chemistry A, ISSN 1089-5639, E-ISSN 1520-5215, Vol. 107, p. 4373-4380Article in journal (Refereed)
  • 49.
    Lomoth, Reiner
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Physical Chemistry.
    Magnusson, Ann
    Xu, Yunhua
    Sun, Licheng
    Mixed-Valance Properties of an Acetate-Bridged Dinuclear Ruthenium (II,II) Complex2003In: Journal of Physical Chemistry A, ISSN 1089-5639, E-ISSN 1520-5215, Vol. 107, p. 4373-4380Article in journal (Refereed)
  • 50.
    Lomoth, Reiner
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science.
    Ott, Sascha
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science.
    Introducing a dark reaction to photochemistry: photocatalytic hydrogen from [FeFe] hydrogenase active site model complexes2009In: Dalton Transactions, ISSN 1477-9226, E-ISSN 1477-9234, no 45, p. 9952-9959Article in journal (Refereed)
    Abstract [en]

    The light-driven splitting of water into its constituting elements gives access to a valuable fuel from an abundant substrate, using sunlight as the only energy source. Synthetic diiron complexes as functional models of the [FeFe] hydrogenase H(2)ase enzyme active site have moved into the centre of focus as potentially viable catalysts for the reductive side of this process, i.e. the reduction of protons to molecular hydrogen. The active site of the enzyme, as well as its mimics in an artificial system, are required to accumulate two electrons from single electron transfer events and to combine them with two protons to form hydrogen. Whereas in biology this reaction is not coupled to photosynthesis and thus proceeds in the dark, additional aspects need to be considered when designing a functional artificial system for the light-driven reduction of protons. Suitable photosensitizers have to be chosen that not only provide sufficient driving force for the reduction of the synthetic diiron catalyst, but also allow for selective excitation to minimize photodegradation. Electron transfer efficiencies have to be optimized for all steps and the sequential nature of the catalyst reduction requires a sufficient stability of potentially labile intermediates of the catalytic cycle. In this perspective, systems for the light-driven conversion of protons to molecular hydrogen are discussed where the catalyst is based on model complexes of the [FeFe] H(2)ase active site. Covalently linked dyads, supramolecular assemblies and multi-component systems will be examined with an emphasis on mechanistic electron transfer schemes, the properties of the individual components, their scope and their potential limitations.

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