| 1. |
- Borgstrom, M., et al.
(författare)
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Electron donor-acceptor dyads and triads based on tris(bipyridine)ruthenium(II) and benzoquinone : Synthesis, characterization, and photoinduced electron transfer reactions
- 2003
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Ingår i: Inorganic Chemistry. - : American Chemical Society (ACS). - 0020-1669 .- 1520-510X. ; 42:17, s. 5173-5184
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Tidskriftsartikel (refereegranskat)abstract
- Two electron donor-acceptor triads based on a benzoquinone acceptor linked to a light absorbing [Ru(bpy)(3)](2+) complex have been synthesized. In triad 6 (denoted Ru-II-BQ-Co-III), a [Co(bpy)(3)](3+) complex, a potential secondary acceptor, was linked to the quinone. In the other triad, 8 (denoted PTZ-Ru-II-BQ), a phenothiazine donor was linked to the ruthenium moiety. The corresponding dyads Ru-II-BQ (4) and PTZ-Ru-II (9) were prepared for comparison. Upon light excitation in the visible band of the ruthenium moiety, electron transfer to the quinone occurred with a rate constant k(1) = 5 x 10(9) s(-1) (tau(1) = 200 ps) in all the quinone containing complexes. Recombination to the ground state followed, with a rate constant k(b) similar to 4.5 x 10(8) s(-1) (tau(b) similar to 2.2 ns), for both Ru-II-BQ and Ru-II-BQ-Co-III with no indication of a charge shift to generate the reduced Coll moiety. In the PTZ-Ru-II-BQ triad, however, the initial charge separation was followed by a rapid (k > 5 x 10(9) s(-1)) electron transfer from the phenothiazine moiety to give the fairly long-lived PTZ(.+)-Ru-II-BQ(.-) state (tau = 80 ns) in unusually high yield for a [Ru(bPY)(3)](2+)- based triad (> 90%), that lies at DeltaGdegrees = 1.32 eV relative to the ground state. Unfortunately, this triad turned out to be rather photolabile. Interestingly, coupling between the oxidized PTZ(.+) and the BQ(.-) moieties seemed to occur. This discouraged further extension to incorporate more redox active units. Finally, in the dyad PTZ-Ru-II a reversible, near isoergonic electron transfer was observed on excitation. Thus, a quasiequilibrium was established with an observed time constant of 7 ns, with ca. 82% of the population in the PTZ-Ru-*(II) state and 18% in the PTZ(.+)Ru(II)(bpy(.-)) state. These states decayed in parallel with an observed lifetime of 90 ns. The initial electron transfer to form the PTZ(.+)-Ru-II(bpy(.-)) state was thus faster than what would have been inferred from the Ru-*(II) emission decay (tau = 90 ns). This result suggests that reports for related PTZ-Ru-II and PTZ-Ru-II-acceptor complexes in the literature might need to be reconsidered.
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| 2. |
- He, Jianjun, et al.
(författare)
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Modified phthalocyanines for efficient near-IR sensitization of nanostructured TiO2 electrode
- 2002
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Ingår i: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 0002-7863 .- 1520-5126. ; 124:17, s. 4922-4932
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Tidskriftsartikel (refereegranskat)abstract
- A zinc phthalocyanine with tyrosine substituents (ZnPcTyr), modified for efficient far-red/near-IR performance in dye-sensitized nanostructured TiO2 solar cells, and its reference, glycine-substituted zinc phthalocyanine, (ZnPcGly), were synthesized and characterized. The compounds were studied spectroscopically, electrochemically, and photoelectrochemically. Incorporating tyrosine groups into phthalocyanine makes the dye ethanol-soluble and reduces surface aggregation as a result of steric effects. The performance of a solar cell based on ZnPcTyr is much better than that based on ZnPcGly. Addition of 3alpha,7alpha-dihydroxy-5beta-cholic acid (cheno) and 4-tert-butylpyridine (TBP) to the dye solution when preparing a dye-sensitized TiO2 electrode diminishes significantly the surface aggregation and, therefore, improves the performance of solar cells based on these phthalocyanines. The highest monochromatic incident photo-to-current conversion efficiency (IPCE) of similar to24% at 690 nm and an overall conversion efficiency (eta) of 0.54% were achieved for a cell based on a ZnPcTyr-sensitized TiO2 electrode. Addition of TBP in the electrolyte decreases the IPCE and eta considerably, although it increases the open-circuit photovoltage. Time-resolved transient absorption measurements of interfacial electron-transfer kinetics in a ZnPoTyr-sensitized nanostructured 702 thin film show that electron injection from the excited state of the dye into the conduction band of TiO2 is completed in similar to500 fs and that more than half of the injected electrons recombines with the oxidized dye molecules in similar to300 ps. In addition to surface aggregation, the very fast electron recombination is most likely responsible for the low performance of the solar cell based on ZnPcTyr.
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| 3. |
- Huang, Ping, et al.
(författare)
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Photo-induced oxidation of a dinuclear Mn-2(II,II) complex to the Mn-2(III,IV) state by inter- and intramolecular electron transfer to Ru-III tris-bipyridine
- 2002
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Ingår i: Journal of Inorganic Biochemistry. - 0162-0134 .- 1873-3344. ; 91:1, s. 159-172
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Tidskriftsartikel (refereegranskat)abstract
- To model the structural and functional parts of the water oxidizing complex in Photosystem 11, a dimeric manganese(II,11) complex (1) was linked to a ruthenium(II)tris-bipyridine (Ru-II(bpy)3) complex via a substituted L-tyrosine, to form the trinuclear complex 2 [J. Inorg. Biochem. 78 (2000) 15]. Flash photolysis of 1 and Ru-II(bpy), in aqueous solution, in the presence of an electron acceptor, resulted in the stepwise extraction of three electrons by Ru-III(bpy), from the Mn-2(II,II) dimer, which then attained the Mn-2(III,IV) oxidation state. In a similar experiment with compound 2, the dinuclear Mn complex reduced the photo-oxidized Ru moiety via intramolecular electron transfer on each photochemical event. From EPR it was seen that 2 also reached the Mn-2(III,IV) state. Our data indicate that oxidation from the Mn-2(II,II) state proceeds stepwise via intermediate formation of Mn-2(II,III) and Mn-2(III,III). In the presence of water, cyclic voltammetry showed an additional anodic peak beyond Mn-2(II,III/III,III) oxidation which was significantly lower than in neat acetonitrile. Assuming that this peak is due to oxidation to Mn-2(III,IV), this suggests that water is essential for the formation of the Mn-2(III,IV) oxidation state. Compound 2 is a structural mimic of the water oxidizing complex, in that it links a Mn complex via a tyrosine to a highly oxidizing photosensitizer. Complex 2 also mimics mechanistic aspects of Photosystem 11, in that the electron transfer to the photosensitizer is fast and results in several electron extractions from the Mn moiety.
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| 4. |
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| 5. |
- Johansson, O., et al.
(författare)
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Electron donor-acceptor dyads based on ruthenium(II) bipyridine and terpyridine complexes bound to naphthalenediimide
- 2003
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Ingår i: Inorganic Chemistry. - : American Chemical Society (ACS). - 0020-1669 .- 1520-510X. ; 42:9, s. 2908-2918
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Tidskriftsartikel (refereegranskat)abstract
- Two series of photosensitizer-electron acceptor complexes have been synthesized and fully characterized: ruthenium(11) tris(bipyridine) {[Ru-II(bpy)(2)(bpy-X-NDI)], where X = -CH2-, tolylene, or phenylene, bpy is 2,2'-bipyridine, and NDI is naphthalenediimide} and ruthenium(II) bis(terpyridine) {[Ru-II(Y-tpy)(tpy-X-NDI)], where Y = H or tolyl and X = tolylene or phenylene, and tpy = 2,2':6',2-terpyridine}. The complexes have been studied by cyclic and differential pulse voltammetry and by steady state and time-resolved absorption and emission techniques. Rates for forward and backward electron transfer have been investigated, following photoexcitation of the ruthenium(II) polypyridine moiety. The terpyridine complexes were only marginally affected by the linked diimide unit, and no electron transfer was observed. In the bipyridine complexes we achieved efficient charge separation. For the complexes containing a phenyl link between the ruthenium(II) and diimide moieties, our results suggest a biphasic forward electron-transfer reaction, in which 20% of the charge-separated state was formed via population of the naphthalenediimide triplet state.
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| 6. |
- Lomoth, R., et al.
(författare)
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Mixed-valence properties of an acetate-bridged dinuclear ruthenium (II,III) complex
- 2003
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Ingår i: Journal of Physical Chemistry A. - : American Chemical Society (ACS). - 1089-5639 .- 1520-5215. ; 107:22, s. 4373-4380
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Tidskriftsartikel (refereegranskat)abstract
- The mixed-valence dinuclear ruthenium complex [Ru-2(bpmp)(mu-OAc)(2)](2+) (where blimp is the phenolate anion of 2,6-bis[bis(2-pyridylmethyl) aminomethyl]-4-methylphenol, H-bpmp) has been studied by UV-Vis-NIR, IR, and EPR spectroscopic and electrochemical techniques. The Ru-2(II,III) complex undergoes reversible one-electron reduction (E-1/2 = -0.61 V vs Fc(+/0)) and oxidation (E-1/2 = 0.09 V vs Fc(+/0)), resulting in the Ru-2(II,III) and Ru-2(III,III) complexes, respectively. A comproportionation constant of K-c = 1.10 x 10(12) (DeltaG(c)degrees = -68 kJ mol(-1)) indicates considerable stability of the mixed-valence state. The paramagnetic complex displays a rhombic EPR spectrum (g(1) = 2.492; g(2) = 2.242; g(3) = 1.855) arising from a ground state in a S = 1/2 low spin system in a low symmetry environment. Three intense, distinguishable intervalence bands are observed in the NIR to mid-IR spectrum of [Ru-2(bpmp)(mu-OAc)(2)](2+) at 3765 cm(-1) (epsilon = 1840 M(-1)cm(-1)), 5615 cm(-1) (epsilon = 10590 M-1cm-1), and 7735 cm-1 (E = 3410 M-1cm-1). All intervalence bands are symmetric but more narrow than predicted for the classical limit and independent of solvent polarity. The results of the spectroscopic and electrochemical characterization indicate that [RU2(bpmp)(mu-OAc)(2)](2+) is either electronically delocalized (class III, H-ab = 1880 cm(-1)) or at the borderline between localization and delocalization (class II-III, H-ab greater than or equal to 590 cm(-1)) with rapid electron transfer (k(ET) > 4 x 10(12) s(-1)) decoupled from solvent reorientation but with a residual activation barrier (E-a less than or equal to 440 cm(-1)) from inner reorganization.
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| 7. |
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| 8. |
- Lomoth, R., et al.
(författare)
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Synthesis and characterization of a dinuclear manganese(III,III) complex with three phenolate ligands
- 2002
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Ingår i: European Journal of Inorganic Chemistry. - 1434-1948 .- 1099-1948. ; 2002:11, s. 2965-2974
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Tidskriftsartikel (refereegranskat)abstract
- A dinuclear manganese complex ([Mn2L(mu-OAc)(2)]PF6) has been synthesized, where L is the trianion of 2,6-bis{[(2-hydroxy-3,5-di- tert-butylbenzyl) (2-pyridylmethyl) amino] methyl)-4-methylphenol, a ligand with three phenolate groups. The two pseudo-octahedrally coordinated Mn ions are bridged via the two bidentate acetate ligands and the 4-methylphenolate group of the ligand. We have characterized the complex with electrochemistry, spectroelectrochemistry and EPR spectroscopy. Electrochemically the Mn-2(III,III) complex undergoes two metal-centered quasi-reversible one-electron reduction steps (E-1/2 = 0.04 and -0.32 V vs. SCE). Reduction to the Mn-2(II,III) state results in transformation into a modified complex with slightly different redox properties. One-electron oxidation (E-1/2 = 0.96 V vs. SCE) affords the Mn-2(III,IV) state while further one-electron oxidation (E-1/2 = 1.13 V vs. SCE) presumably involves ligand oxidation. High valent Mn complexes involving Mn-IV or Mn-V centers are of particular interest as intermediates in catalytic water oxidation. The redox potentials of [Mn2L(mu-OAC)(2)](+) show the expected stabilization of higher manganese oxidation states compared with the related complex, [Mn-2(bpmp)(mu-OAc)(2)](+).
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