| 1. |
- Li, Cheng, et al.
(författare)
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Photochemical hydrogen production catalyzed by polypyridyl ruthenium-cobaloxime heterobinuclear complexes with different bridges
- 2009
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Ingår i: Journal of Organometallic Chemistry. - : Elsevier BV. - 0022-328X .- 1872-8561. ; 694:17, s. 2814-2819
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Tidskriftsartikel (refereegranskat)abstract
- Two heterobinuclear complexes [(bpy)(2)Ru(bpy-4-CH3,4'-CONH(4-py)Co(dmgBF(2))(2)(OH2)](PF6)(2) (1, dmgBF(2) = (difluoroboryl) dimethylglyoximato) and [(bpy)(2)Ru(bpy-4-CH3,4'-CONHCH2(4-py)Co(dmgBF(2))(2)(OH2)](PF6)(2) (2) were prepared, in which the polypyridyl ruthenium photosensitizer and the cobaloxime catalyst are connected either by a conjugated bridge (1) or by an unconjugated one (2). Complexes 1 and 2 were used as photocatalysts for hydrogen generation. Under optimal conditions, the turnover numbers (ton) for hydrogen evolution were 38 for 1 and 48 for 2 in the presence of 300 equiv of both Et3N and [Et3NH][BF4] in the acetone solution during an 8-h irradiation of visible light (lambda > ca. 400 nm). The complex 2 with an unconjugated bridge proved to be more efficient for photochemical hydrogen generation than the complex 1 with a conjugated bridge under the same reaction condition.
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| 2. |
- Na, Yong, et al.
(författare)
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Visible light-driven electron transfer and hydrogen generation catalyzed by bioinspired 2Fe2S complexes
- 2008
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Ingår i: Inorganic Chemistry. - : American Chemical Society (ACS). - 0020-1669 .- 1520-510X. ; 47:7, s. 2805-2810
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Tidskriftsartikel (refereegranskat)abstract
- Complexes [{(mu-SCH2)(2)NCH2C6H5){Fe(CO)(2)L-1){Fe(CO)(2)L-2}] (L-1 = CO, L-2 = P(Pyr)(3), 2; L-1 = L-2 = P(Pyr)(3), 3) were prepared, which have the lowest reduction potentials for the mono- and double-CO-displaced diiron complexes reported so far. Hydrogen evolution, driven by visible light, was successfully observed for a three-component system, consisting of a ruthenium polypyridine complex, the biomimetic model complex 2 or 3, and ascorbic acid as both electron and proton donor in CH3CN/H2O. The electron transfer from photogenerated Ru(bPY)(3)(+) to 2 or 3 was detected by laser flash photolysis. Under optimal conditions, the total turnover number for hydrogen evolution was 4.3 based on 2 and 86 based on Ru(bPY)(3)(2+) in a three-hour photolysis.
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| 3. |
- Billsten, Helena, et al.
(författare)
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Excited-state processes in the carotenoid zeaxanthin after excess energy excitation
- 2005
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Ingår i: The Journal of Physical Chemistry Part A: Molecules, Spectroscopy, Kinetics, Environment and General Theory. - : American Chemical Society (ACS). - 1520-5215. ; 109:31, s. 6852-6859
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Tidskriftsartikel (refereegranskat)abstract
- Aiming for better understanding of the large complexity of excited-state processes in carotenoids, we have studied the excitation wavelength dependence of the relaxation dynamics in the carotenoid zeaxanthin. Excitation into the lowest vibrational band of the S-2 state at 485 nm, into the 0-3 vibrational band of the S2 state at 400 nm, and into the B-2(u)+ state at 266 nm resulted in different relaxation patterns. While excitation at 485 nm produces the known four-state scheme (S-2 -> hot S-1 -> S-1 -> S-0), excess energy excitation led to additional dynamics occurring with a time constant of 2.8 ps (400 nm excitation) and 4.9 ps (266 nm excitation), respectively. This process is ascribed to a conformational relaxation of conformers generated by the excess energy excitation. The zeaxanthin S* state was observed regardless of the excitation wavelength, but its population increased after 400 and 266 nm excitation, suggesting that conformers generated by the excess energy excitation are important for directing the population toward the S* state. The S-2-S-1 internal conversion time was shortened from 135 to 70 fs when going from 485 to 400 nm excitation, as a result of competition between the S-2-S-1 internal conversion from the vibrationally hot S2 state and S2 vibrational relaxation. The S, lifetime of zeaxanthin was within experimental error the same for all excitation wavelengths, yielding similar to 9 ps. No long-lived species have been observed after excitation by femtosecond pulses regardless of the excitation wavelength, but excitation by nanosecond pulses at 266 nm generated both zeaxanthin triplet state and cation radical.
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| 4. |
- Li, Chaoyan, et al.
(författare)
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Anthraquinone dyes as photosensitizers for dye-sensitized solar cells
- 2007
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Ingår i: Solar Energy Materials and Solar Cells. - : Elsevier BV. - 0927-0248 .- 1879-3398. ; 91:19, s. 1863-1871
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Tidskriftsartikel (refereegranskat)abstract
- Three anthraquitione dyes with carboxylic acid as anchoring group are designed and synthesized as sensitizers for dye-sensitized solar cells (DSSCs). Preliminary photophysical and photoelectrochemical measurements show that these anthraquinone dyes have very low performance on DSSC applications, although they have broad and intense absorption spectra in the visible region (up to 800nm). Transient absorption kinetics, fluorescence lifetime measurements and density functional theory (DFT) calculations are conducted to investigate the cause of such low DSSC performance for these dyes. The results show that the strong electron -withdrawing character of the two carbonyl groups on anthraquinone framework may lie behind the low performance by suppressing the efficient electron injection from the dye to the conduction band of TiO2.
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| 5. |
- Li, Minna, et al.
(författare)
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Oligo thiophene-2-yl-vinyl bridged mono- and binuclear ruthenium(II) tris-bipyridine complexes : Synthesis, photophysics, electrochemistry and electrogenerated chemiluminescence
- 2008
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Ingår i: Journal of Organometallic Chemistry. - : Elsevier BV. - 0022-328X .- 1872-8561. ; 693:1, s. 46-56
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Tidskriftsartikel (refereegranskat)abstract
- A series of mono- and binuclear ruthenium(II) tris-bipyridine complexes tethered to oligothienylenevinyleries have been synthesized and characterized by H-1 NMR, C-13 NMR and TOF-MS spectrometry. Photophysics, electrochemistry and electrogenerated chemiluminescence (ECL) properties of these complexes are investigated. The electronic absorption spectra of the mononuclear ruthenium complexes show a significant red shift both at MLCT (metal-to-ligand charge transfer) and pi-pi* transitions of oligothienylenevinylenes with increase in the number of thiophenyl-2-yl-vinyl unit. For the binuclear complexes these two absorption bands are overlapped.) All the metal complexes have very weak emission compared to that of the reference complex Ru(bpy)(3)(2+). The first reduction potentials of all mononuclear ruthenium complexes are less negative than that of Ru(bpy)(3)(2+), due to the moderate electron-withdrawing effect of oligothienylenevinylenes. For binuclear ruthenium complexes, only one Ru(II/III) oxidation peak (E-1/2=0.96V vs. Ag/Ag+) was observed, suggesting a weak interaction between two metal centers. Three successive reduction processes of bipyridine ligands are similar among all ruthenium complexes except for RuTRu, which has a very sharp peak owing to the accumulation of neutral product oil the electrode surface. All these ruthenium complexes exhibited different ECL property in CH3CN solution without any additional reductant or oxidant. For three mononuclear ruthenium complexes, the ECL intensity strengthens with increase in the number of thiophene-2-yl-vinyl unit. However, the ECL efficiency dramatically decreased in the binuclear ruthenium complexes. The ECL efficiencies of all the)2+, reported complexes do not exceed that of Ru(bpy 3 where the ECL efficiency decreases in the order of RuTRu > Ru3T > Ru2T > RuT > Ru2TRu (RuT, bis-2,2'-bipyridyl-(4-metliyl-4'-(2-thienylethenyl)-2,2'-bipyridine) ruthenium dihexafluorophosphate; Ru2T, bis-2,2'-bipyridyl-(4-methyl-4'-{(E) -2-[5-((E) -2-thienylethenyl)-thienylethenyl])-2,2'-bipyridine)ruthenium dihexafluorophosphate; Ru3T, bis-2,2'-bipyridyl-(4-methyl-4'-[(E)-2-{(E)-2-[5-((E)-2-thienylethenyl)- thienylethenyl])}-2,2'-bipyridine) ruthenium dihexafluorophosphate; RuTRu, bis-2,2'-bipyridyl-ruthenium-bis-[2-((E)-4'-methyl-2,2'-bipyridinyl-4)-e thenyl]-thienyl-bis-2,2'-bipyridyl-ruthenium tetrahexafluorophosphate; Ru2TRu, bis-2,2'-bipyridyl-ruthenium-(E)-1,2-bis-{2-[2-((E)-4'-methyl-2,2'-bipyr idinyl-4)-ethenyl]-thienyl}ethenyl-bis-2,2'-bipyridyl-ruthenium tetrahexafluorophosphate).
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| 6. |
- Li, Ping, et al.
(författare)
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FeFe -Hydrogenase active site models with relatively low reduction potentials : Diiron dithiolate complexes containing rigid bridges
- 2008
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Ingår i: Journal of Inorganic Biochemistry. - : Elsevier BV. - 0162-0134 .- 1873-3344. ; 102:4, s. 952-959
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Tidskriftsartikel (refereegranskat)abstract
- Three diiron dithiolate complexes containing rigid and conjugated bridges, [mu-SC6H4-2-(CO)S-mu]Fe-2(CO)(6) (1), [2-mu-SC5H3N-3-(CO)S-mu]Fe-2(CO)(6) (2). and the PPh3-monosubstituted complex [mu-SC6H4-2-(CO)S-mu]Fe-2(CO)(5)(PPh3) (1-P), were prepared as biomimetic models for the [FeFe]-hydrogenase active site. The structures of complexes 1 and 2 were determined by single crystal X-ray analysis, which shows that each complex features a rigid coplanar dithiolate bridge with a 2-3 degrees deviation from the bisect plane of the molecule. The influence of the rigid bridge on the reduction potentials of complexes 1, 2 and 1-P was investigated by electrochemistry. The cyclic voltammograms of complexes 1 and 2 display large positive shifts for the primary reduction potentials, that is, 380-480 mV in comparison to that of the pdt-bridged (pdt = propane-1,3-dithiolato) complex (mu-pdt)Fe-2(CO)(6) and 160-260 mV to that of the bdt-bridged (bdt = benzene- 1,2-dithiolato) analogue ([mu-bdt)Fe-2(CO)(6).
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| 7. |
- Li, Xueqiang, et al.
(författare)
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Noncovalent assembly of a metalloporphyrin and an iron hydrogenase active-site model : Photo-induced electron transfer and hydrogen generation
- 2008
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Ingår i: Journal of Physical Chemistry B. - : American Chemical Society (ACS). - 1520-6106 .- 1520-5207 .- 1089-5647. ; 112:27, s. 8198-8202
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Tidskriftsartikel (refereegranskat)abstract
- A noncovalent assembly of a pyridyl-functionalized hydrogenase active-site model complex and zinc tetraphenylporphyrin has been obtained and characterized. Upon light irradiation, fluorescence quenching by electron transfer was observed from the singlet excited state of the porphyrin to the diiron center, and the mechanism was verified by fluorescence lifetime and transient absorption spectroscopic measurements. In contrast to molecular dyads linked by covalent bonds, the assembled system was designed to avoid charge recombination via complex dissociation after photo-induced electron transfer. Visible light-driven hydrogen generation was observed from this self-assembled system. The assembling strategy employed in this study has the potential to be used for any other hydrogenase models in the future.
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| 8. |
- Liu, Xien, et al.
(författare)
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Synthesis, electrochemical, and photophysical studies of multicomponent systems based on porphyrin and ruthenium(II) polypyridine complexes
- 2007
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Ingår i: Tetrahedron. - : Elsevier BV. - 0040-4020 .- 1464-5416. ; 63:37, s. 9195-9205
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Tidskriftsartikel (refereegranskat)abstract
- Two ruthenium tris-bipyridine functionalized porphyrins 4, 8 and their Zn derivatives 4-Zn, 8-Zn were designed, synthesized, and characterized. The redox potentials of these complexes as well as their corresponding monomeric reference porphyrin and ruthenium bipyridine complexes were also measured for comparison. Primary dynamic studies on the electron injection and backing recombination between these complexes and TiO2 nanoparticles were carried out by means of transient absorption spectroscopy. The results indicate that a long-lived charge separation state was obtained in these assemblies.
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| 9. |
- Na, Yong, et al.
(författare)
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Intermolecular electron transfer from photogenerated Ru(bpy)(3)(+) to 2Fe2S model complexes of the iron-only hydrogenase active site
- 2007
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Ingår i: Inorganic Chemistry. - : American Chemical Society (ACS). - 0020-1669 .- 1520-510X. ; 46:10, s. 3813-3815
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Tidskriftsartikel (refereegranskat)abstract
- Visible light-driven intermolecular electron transfer was observed from a reduced species Ru(bpy)(3)(+), photogenerated via a reductive quenching of the ruthenium photosensitizer by a diethyldithiocarbamate anion, to bioinspired [2Fe2S] model complexes of the iron-only hydrogenase active site. The results indicate that Ru(bpy)(3)(2+) can act as a photoactive functional model of the [4Fe4S] cluster, playing the role of an electron-transfer relay. The photogenerated (FeFe0)-Fe-I species, which is proposed to be a crucial intermediate for proton reduction catalyzed electrochemically by the [2Fe2S] complexes, gives promise in the light-driven dihydrogen evolution using diiron complexes as surrogates of noble platinum catalysts.
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| 10. |
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