| 1. |
- Antila, Liisa J., et al.
(författare)
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Dynamics and Photochemical H-2 Evolution of Dye-NiO Photocathodes with a Biomimetic FeFe-Catalyst
- 2016
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Ingår i: ACS Energy Letters. - : American Chemical Society (ACS). - 2380-8195. ; 1:6, s. 1106-1111
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Tidskriftsartikel (refereegranskat)abstract
- Mesoporous NiO films were cosensitized with a coumarin 343 dye and a proton reduction catalyst of the [Fe-2(CO)(6)(bdt)] (bdt = benzene-1,2-dithiolate) family. Femtosecond ultraviolet visible transient absorption experiments directly demonstrated subpicosecond hole injection into NiO from excited dyes followed by rapid (t(50%) similar to 6 ps) reduction of the catalyst on the surface with similar to 70% yield. The reduced catalyst was long-lived (2 mu s to 20 ms), which may allow protonation and a second reduction step of the catalyst to occur. A photo electrochemical device based on this photocathode produced H-2 with a Faradaic efficiency of similar to 50%. Fourier transform infrared spectroscopy and gas chromatography experiments demonstrated that the observed device deterioration with time was mainly due to catalyst degradation and desorption from the NiO surface. The insights gained from these mechanistic studies, regarding development of dye-catalyst cosensitized photocathodes, are discussed.
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| 2. |
- Arkhypchuk, Anna I., et al.
(författare)
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One-Pot Intermolecular Reductive Cross-Coupling of Deactivated Aldehydes to Unsymmetrically 1,2-Disubstituted Alkenes
- 2018
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Ingår i: Organic Letters. - : American Chemical Society (ACS). - 1523-7060 .- 1523-7052. ; 20:17, s. 5086-5089
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Tidskriftsartikel (refereegranskat)abstract
- The phospha-Peterson reaction between a lithiated secondary phosphane, MesP(Li)TMS, and an aldehyde affords Mes-phosphaalkenes which, upon methanol addition and P-oxidation, react with a second carbonyl compound site specifically to produce unsymmetric alkenes. The E/Z selectivity of the one-pot cross coupling is largely determined by the electronic nature of the aryl substituent of the first aldehyde, with electron-donating groups giving rise to increased amounts of Z-alkenes.
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| 3. |
- Arkhypchuk, Anna I., et al.
(författare)
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Triarylalkenes from the site-selective reductive cross-coupling of benzophenones and aldehydes
- 2019
-
Ingår i: Chemical Communications. - : Royal Society of Chemistry (RSC). - 1359-7345 .- 1364-548X. ; 55:43, s. 6030-6033
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Tidskriftsartikel (refereegranskat)abstract
- PhP(Li)TMS converts benzophenones to phosphaalkenes which upon activation under oxidizing, basic conditions react with aromatic aldehydes under the formation of triarylalkenes. The one-pot reaction omits transition metals, proceeds at room temperature and precludes the formation of any homo-coupling products. Systematic substrate variations reveal reactivity patterns that are useful for the identification of ketone/aldehyde combinations that can be coupled in yields up to 80%.
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| 4. |
- Arkhypchuk, Anna I., et al.
(författare)
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Versatile Approach to 3-Phosphahexatrienes Bearing Low Coordinated Phosphorus
- 2015
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Ingår i: Phosphorus Sulfur and Silicon and the Related Elements. - : Informa UK Limited. - 1042-6507 .- 1563-5325. ; 190:5-6, s. 638-646
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Tidskriftsartikel (refereegranskat)abstract
- lambda(3)-phosphahexatrienes were prepared from ethoxyvinyl phosphinophosphonates using the phospha-Wittig-Horner reaction. The title compounds can be easily prepared in three steps starting from dichlorophosphines with good overall yields. Although these were found to be thermally unstable, these can be trapped, for instance, with methanol. The resulting methoxyphosphines are isolated in high yields in case of aldehyde starting materials with more bulky substituents.
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| 5. |
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| 6. |
- Bedin, Michele, et al.
(författare)
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Synthesis and properties of a heterobimetallic iron-manganese complex and its comparison with homobimetallic analogues
- 2019
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Ingår i: Inorganica Chimica Acta. - : ELSEVIER SCIENCE SA. - 0020-1693 .- 1873-3255. ; 490, s. 254-260
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Tidskriftsartikel (refereegranskat)abstract
- Heterobimetallic cofactors containing one manganese and one iron ion have recently been found within the di-metal carboxylate protein family. Herein we report the synthesis and characterization of three binuclear metal complexes with Fe-Fe, Mn-Mn, and Fe-Mn metal composition. All three complexes use the same ligand framework, the BPMP ligand (HBPMP=2,6-bis[(bis (-2-pyridylmethyl)amine) methyl]-4-methylphenol)) with two additional acetate ligands bridging the two metals. In terms of stability towards metal exchange, the Fe-Mn is more stable than the Mn-Mn complex but less stable than the Fe-Fe complex. Cyclic voltammetry shows that the Fe-Mn complex behaves markedly different than the homobimetallic complexes. The Fe-Mn complex also shows higher reactivity with O-2 than both the Fe-Fe and the Mn-Mn counterparts.
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| 7. |
- Bhunia, Asamanjoy, et al.
(författare)
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Formal water oxidation turnover frequencies from MIL-101(Cr) anchored Ru(bda) depend on oxidant concentration
- 2018
-
Ingår i: Chemical Communications. - : ROYAL SOC CHEMISTRY. - 1359-7345 .- 1364-548X. ; 54, s. 7770-7773
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Tidskriftsartikel (refereegranskat)abstract
- The molecular water oxidation catalyst [Ru(bda)(L)(2)] has been incorporated into pyridine-decorated MIL-101(Cr) metal-organic frameworks. The resulting MIL-101@Ru materials exhibit turnover frequencies (TOFs) up to ten times higher compared to the homogenous reference. An unusual dependence of the formal TOFs on oxidant concentration is observed that ultimately arises from differing amounts of catalysts in the MOF crystals being active.
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| 8. |
- Bourrez, Marc, et al.
(författare)
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Concerted proton-coupled electron transfer from a metal-hydride complex
- 2015
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Ingår i: Nature Chemistry. - 1755-4330 .- 1755-4349. ; 7:2, s. 140-145
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Tidskriftsartikel (refereegranskat)abstract
- Metal hydrides are key intermediates in the catalytic reduction of protons and CO2 as well as in the oxidation of H-2. In these reactions, electrons and protons are transferred to or from separate acceptors or donors in bidirectional proton-coupled electron transfer (PCET) steps. The mechanistic interpretation of PCET reactions of metal hydrides has focused on the stepwise transfer of electrons and protons. A concerted transfer may, however, occur with a lower reaction barrier and therefore proceed at higher catalytic rates. Here we investigate the feasibility of such a reaction by studying the oxidation-deprotonation reactions of a tungsten hydride complex. The rate dependence on the driving force for both electron transfer and proton transfer-employing different combinations of oxidants and bases-was used to establish experimentally the concerted, bidirectional PCET of a metal-hydride species. Consideration of the findings presented here in future catalyst designs may lead to more-efficient catalysts.
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| 9. |
- Brown, Allison, et al.
(författare)
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Ultrafast Electron Transfer between Dye and Catalyst on a Mesoporous NiO Surface
- 2016
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Ingår i: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 0002-7863 .- 1520-5126. ; 26, s. 8060-8063
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- The combination of molecular dyes and catalysts with semiconductors into dye-sensitized solar fuel devices (DSSFDs) requires control of efficient interfacial and surface charge transfer between the components. The present study reports on the light-induced electron transfer processes of p-type NiO films cosensitized with coumarin C343 and a bioinspired proton reduction catalyst, [FeFe](mcbdt)(CO)(6) (mcbdt = 3-carboxybenzene-1,2-dithiolate). By transient optical spectroscopy we find that ultrafast interfacial electron transfer (tau approximate to 200 fs) from NiO to the excited C343 ("hole injection") is followed by rapid (t(1/2) approximate to 10 ps) and efficient surface electron transfer from C343 to the coadsorbed [FeFe] (mcbdt)(CO)(6). The reduced catalyst has a clear spectroscopic signature that persists for several tens of microseconds, before charge recombination with NiO holes occurs. The demonstration of rapid surface electron transfer from dye to catalyst on NiO, and the relatively long lifetime of the resulting charge separated state, suggests the possibility to use these systems for photocathodes on. DSSFDs.
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| 10. |
- Canton, S. E., et al.
(författare)
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Watching the dynamics of electrons and atoms at work in solar energy conversion
- 2015
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Ingår i: Faraday discussions. - : Royal Society of Chemistry. - 1359-6640 .- 1364-5498. ; 185, s. 51-68
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Tidskriftsartikel (refereegranskat)abstract
- The photochemical reactions performed by transition metal complexes have been proposed as viable routes towards solar energy conversion and storage into other forms that can be conveniently used in our everyday applications. In order to develop efficient materials, it is necessary to identify, characterize and optimize the elementary steps of the entire process on the atomic scale. To this end, we have studied the photoinduced electronic and structural dynamics in two heterobimetallic ruthenium-cobalt dyads, which belong to the large family of donor-bridge-acceptor systems. Using a combination of ultrafast optical and X-ray absorption spectroscopies, we can clock the light-driven electron transfer processes with element and spin sensitivity. In addition, the changes in local structure around the two metal centers are monitored. These experiments show that the nature of the connecting bridge is decisive for controlling the forward and the backward electron transfer rates, a result supported by quantum chemistry calculations. More generally, this work illustrates how ultrafast optical and X-ray
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| 11. |
- Das, Biswanath, et al.
(författare)
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Iron Pentapyridyl Complexes as Molecular WaterOxidation Catalysts : Strong Influence of a Chloride Ligandand pH in Altering the Mechanism
- 2016
-
Ingår i: ChemSusChem. - : Wiley. - 1864-5631 .- 1864-564X. ; 9:10, s. 1178-1186
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Tidskriftsartikel (refereegranskat)abstract
- The development of molecular water oxidation catalysts basedon earth-abundant, non-noble metals is essential for artificial photosynthesis research. Iron, which is the most abundant transition metal in the earth's crust, is a prospective candidate for this purpose. Herein, we report two iron complexes based on the polypyridyl ligand Py5OH (Py5OH=pyridine-2,6-diylbis[di(pyridin-2-yl)methanol]) that can catalyse water oxidation to produce O2 in RuIII-induced (at pH 8, highest turnover number (TON)=26.5; turnover frequency (TOF)=2.2 s-1), CeIV-induced(at pH 1.5 highest TON=16; TOF=0.75 s-1) and photo-induced(at pH 8, highest TON=43.5; TOF=0.6 s-1) reactions. A chloride ligand in one of the iron complexes is shown to affect the activity strongly, improve stability and, thereby, the performance at pH 8 but it inhibits oxygen evolution at pH 1.5. The observations are consistent with a change in mechanism for catalytic water oxidation with the Fe(Py5OH) complexes between acidic (CeIV) and near-neutral pH (RuIII).
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| 12. |
- Das, Biswanath, et al.
(författare)
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Structural features of molecular electrocatalysts in multi-electron redox processes for renewable energy : recent advances
- 2019
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Ingår i: Sustainable Energy & Fuels. - : Royal Society of Chemistry (RSC). - 2398-4902. ; 3:9, s. 2159-2175
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Forskningsöversikt (refereegranskat)abstract
- Understanding the structural features of molecular electrocatalysts for carbon dioxide reduction and water oxidation is essential for manufacturing next generation catalysts for renewable energy. We will discuss the crucial structural motifs of those catalysts that have shown novel characteristics in recent years in terms of electrocatalytic efficacy (high TON, TOF and low overpotential), product selectivity and mechanisms. Both inorganic and organic homogeneous catalysts are scrutinized in this review. We will also highlight electrocatalysts with dual activity (i.e. they are able to catalyze both water oxidation and CO2 reduction) as an interesting prospect from the point of view of a single catalyst electrolyzer: a possible design for future easy-to-manufacture effective electrolyzers. This discussion will enrich the overall knowledge on the electrocatalyst design, an important step towards the development of efficient catalysts with cutting edge designs for a renewable energy future and practical applications.
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| 13. |
- Das, Biswanath, et al.
(författare)
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Water oxidation catalysed by a mononuclear CoII polypyridine complex; possible reaction intermediates and the role of the chloride ligand
- 2015
-
Ingår i: Chemical Communications. - : Royal Society of Chemistry (RSC). - 1359-7345 .- 1364-548X. ; 51:66, s. 13074-13077
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Tidskriftsartikel (refereegranskat)abstract
- A mononuclear cobalt(II) complex as a homogeneous molecular catalyst for photochemically, electrochemically and chemically induced oxygen evolution reactions is presented. Experimental evidence points towards the presence of a chloride ligand at the cobalt centre throughout the catalytic cycle, and the temporary detachment of a pyridine ligand to open a coordination site for substrate binding.
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| 14. |
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| 15. |
- D'Imperio, Nicolas, et al.
(författare)
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Triphenylphosphaalkenes in Chemical Equilibria
- 2019
-
Ingår i: European Journal of Inorganic Chemistry. - : Wiley. - 1434-1948 .- 1099-1948 .- 1099-0682. ; :11-12, s. 1562-1566
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Tidskriftsartikel (refereegranskat)abstract
- Triphenylphosphaalkenes 1a-c were prepared in good to excellent yields in a modified phospha-Peterson reaction between PhP(Li)TMS and benzophenones with different para-substituents at the C-phenyl groups (a: R = H, b: R = O-octyl, c: R = F). Owing to the low kinetic stabilization that is provided by the P-phenyl group, compounds 1a-c engage in reversible dimerization and oligomerization reactions, some of which are not detectable by 31P NMR monitoring. The dimers and oligomers are in chemical equilibria with monomeric 1a-c, and can be converted quantitatively to phosphinites 4a-c by the irreversible addition of methanol across the P=C double bond.
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| 16. |
- Esfandiarfard, Keyhan
(författare)
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Novel Organophosphorus Compounds for Materials and Organic Synthesis
- 2017
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis is devoted to the development of new organophosphorus compounds for potential uses in material science and as reagents in Organic Chemistry. Organophosphorus compounds in a single molecule or organic electronics context are appealing as the phosphorous centers perturb the electronic properties of the π-conjugated systems while at the same time provide synthetic handles for subsequent synthetic modifications. As such, new synthetic methodology to such compounds and the exploration of new building blocks is of considerable interest. In a different study, novel organophosphorus compounds are synthesized and shown to promote a reaction in Organic Chemistry that has previously not been possible, i.e. the stereoselective reductive coupling of aldehydes to alkenes. Such developments enlarge the toolkit of reactions that are available to Organic Chemists, and may impact the synthetic routes to pharmaceuticals and other important commodity chemicals.A general introduction of the key structural unit of this thesis, phosphaalkenes, is given in the first chapter. The synthesis, reactivity, properties and applications of these P=C double bond containing compounds are highlighted. The Wittig reaction and its variations as well as the phosphorus analogues that produce phosphaalkenes are outlined in detail.The second chapter is dedicated to the synthesis of a precursor that is used for the preparation of novel π-conjugated, organophosphorus compounds. C,C-Dibromophosphaalkenes are prepared and the halide substituents are used for the selective introduction of acetylene units. Besides the phosphaalkenes, the successful syntheses of two new diphosphenes is presented, indicating a broad applicability of the precursors.The third chapter is dedicated to the isolation of a metal-free phosphanylphosphonate that transforms aldehydes quantitatively to their corresponding E-phosphaalkenes in a transition metal-free phospha-HWE (Horner-Wadsworth-Emmons) reaction. The reaction benefits from mild conditions, high E-stereoselectivity, and a broad substrate scope.In the last chapter, a novel method for the reductive coupling of aldehydes to olefins is introduced. The reaction, which is a vast improvement over the McMurry coupling, allows for the selective synthesis of symmetrical and most importantly unsymmetrical E-alkenes. The phosphanylphosphonate mentioned above is the reagent that facilitates the coupling of the aldehydes via a phosphaalkene intermediate. This one-pot reaction benefits from mild conditions, good conversions, and high E-stereoselectivity.In summary, the thesis presents novel aspects of organophosphorus chemistry. These include the preparations and exploration of interesting precursors for the construction of π-conjugated organophosphorus compounds, and the use of organophosphorus reagents for unprecedented transformations in Organic Chemistry.
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| 17. |
- Esfandiarfard, Keyhan, et al.
(författare)
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Synthesis of 2,6-Dimesitylphenyl-C,C-dibromophosphaalkene
- 2015
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Ingår i: Phosphorus Sulfur and Silicon and the Related Elements. - : Taylor & Francis Group. - 1042-6507 .- 1563-5325. ; 190:5-6, s. 816-820
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Tidskriftsartikel (refereegranskat)abstract
- A facile one-pot transformation of Dmp-I to Dmp-P=CBr2 (Dmp = 2,6-dimesitylphenyl), a valuable precursor for other unsaturated phosphorus compounds, is described. VT-1H-NMR experiments reveal a hindered rotation of the m-terphenyl structure with a rotational barrier of approx. 14 kcal/mol. Bromination of Dmp-I gives selective substitution of all aromatic protons of the mesityl substituents.
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| 18. |
- Esfandiarfard, Keyhan, et al.
(författare)
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Synthesis of the first metal-free phosphanylphosphonate and its use in the "phospha-Wittig-Horner" reaction
- 2016
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Ingår i: Dalton Transactions. - : Royal Society of Chemistry (RSC). - 1477-9226 .- 1477-9234. ; 45:5, s. 2201-2207
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Tidskriftsartikel (refereegranskat)abstract
- The synthesis of the first phophanylphosphonate, Mes*PH-PO(OEt)(2) (2-H), in which the P(III) centre is not coordinated by a M(CO)(5) (M = W, Mo, Cr) fragment is reported. The title compound reacts with LDA under the formation of 2-Li which is best described as the enolate form with a high double bond character between the two phosphorus centres. 2-Li is shown to engage in the phospha-Wittig-Horner reaction and converts aldehydes into phosphaalkenes that are metal-free and thus available for future manipulations at the phophorus lone pair. Using a selection of aldehydes with aliphatic, aromatic or vinylic substituents as substrates, phosphaalkene formation proceeds in high yields and high E-selectivity. The selectivity is however compromised during purification on standard silica which was found to promote E/Z isomerization.
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| 19. |
- Esfandiarfard, Keyhan, et al.
(författare)
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Unsymmetrical E-Alkenes from the Stereoselective Reductive Coupling of Two Aldehydes
- 2017
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Ingår i: Journal of the American Chemical Society. - : AMER CHEMICAL SOC. - 0002-7863 .- 1520-5126. ; 139:8, s. 2940-2943
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Tidskriftsartikel (refereegranskat)abstract
- The unprecedented formation of unsymmetrical alkenes from the intermolecular reductive coupling of two different aldehydes is described. In contrast to the McMurry reaction which affords statistical product mixtures, selectivity in the reported procedure is achieved by a sequential ionic mechanism in which a first aldehyde is reacted with a phosphanylphosphonate to afford a phosphaalkene intermediate which, upon activation by hydroxide, reacts with a second aldehyde to the unsymmetrical E-alkenes. The described reaction is free of transition metals and proceeds under ambient temperature within minutes in good to excellent overall yields. It is a new methodology to use feedstock aldehydes for the direct production of C=C double bond-containing products and may impact how chemists think of multistep synthetic sequences in the future.
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| 20. |
- Fei, Honghan, et al.
(författare)
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Functionalization of robust Zr(IV)-based metal-organic framework films via a postsynthetic ligand exchange
- 2015
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Ingår i: Chemical Communications. - : Royal Society of Chemistry (RSC). - 1359-7345 .- 1364-548X. ; 51:1, s. 66-69
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Tidskriftsartikel (refereegranskat)abstract
- A facile and efficient fabrication approach for homogeneous, crack-free UiO-66 films with exceptionally high crystallinity and tunable thickness on a transparent and conductive glass substrate is reported. Two functionalized species, a catechol ligand and a Fe-2 complex with structural resemblance to the active site of [FeFe] hydrogenase, were introduced into the MOF films via a postsynthetic exchange. Voltammetric studies show the [FeFe] complex in the thinner UiO-66 films (2-5 mu m) can be reduced electrochemically.
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| 21. |
- Finke, Aaron D., et al.
(författare)
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The 6,6-Dicyanopentafulvene Core : A Template for the Design of Electron-Acceptor Compounds
- 2015
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Ingår i: Chemistry - A European Journal. - : Wiley. - 0947-6539 .- 1521-3765. ; 21:22, s. 8168-8176
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Tidskriftsartikel (refereegranskat)abstract
- The electron-accepting ability of 6,6-dicyanopentafulvenes (DCFs) can be varied extensively through substitution on the five-membered ring. The reduction potentials for a set of 2,3,4,5-tetraphenyl-substituted DCFs, with varying substituents at the para-position of the phenyl rings, strongly correlate with their Hammett sigma(p)-parameters. By combining cyclic voltammetry with DFT calculations ((U)B3LYP/6-311+G(d)), using the conductor-like polarizable continuum model (CPCM) for implicit solvation, the absolute reduction potentials of a set of twenty DCFs were reproduced with a mean absolute deviation of 0.10eV and a maximum deviation of 0.19eV. Our experimentally investigated DCFs have reduction potentials within 3.67-4.41eV, however, the computations reveal that DCFs with experimental reduction potentials as high as 5.3eV could be achieved, higher than that of F-4-TCNQ (5.02eV). Thus, the DCF core is a template that allows variation in the reduction potentials by about 1.6eV.
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| 22. |
- Fluch, Ulrike, et al.
(författare)
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Post synthetic exchange enables orthogonal click chemistry in a metal organic framework
- 2019
-
Ingår i: Dalton Transactions. - : ROYAL SOC CHEMISTRY. - 1477-9226 .- 1477-9234. ; 48:1, s. 45-49
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Tidskriftsartikel (refereegranskat)abstract
- Biphenyl-4,4'-dicarboxylic acid derivatives containing either azide or acetylene functional groups were inserted into UiO-67 metal organic frameworks (MOFs) via post synthetic linker exchange. Sequential and orthogonal click reactions could be performed on these modified MOFs by incubating the crystals with small molecule substrates bearing azide or acetylene groups in the presence of a copper catalyst. H-1 NMR of digested MOF samples showed that up to 50% of the incorporated linkers could be converted to their "clicked" triazole products. Powder X-ray diffraction confirmed that the UiO-67 structure was maintained throughout all transformations. The click reaction efficiency is discussed in context of MOF crystallite size and pore size. As the incorporation of clicked linkers could be controlled by post synthetic exchange, this work introduces a powerful method of quickly introducing orthogonal modifications into known MOF architectures.
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| 23. |
- Fluch, Ulrike, et al.
(författare)
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Uniform distribution of post-synthetic linker exchange in metal-organic frameworks revealed by Rutherford backscattering spectrometry
- 2017
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Ingår i: Chemical Communications. - : ROYAL SOC CHEMISTRY. - 1359-7345 .- 1364-548X. ; 53:48, s. 6516-6519
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Tidskriftsartikel (refereegranskat)abstract
- Rutherford backscattering spectrometry (RBS) has been used for the first time to study post-synthetic linker exchange (PSE) in metal-organic frameworks. RBS is a non-invasive method to quantify the amount of introduced linker, as well as providing a means for depth profiling in order to identify the preferred localization of the introduced linker. The exchange of benzenedicarboxylate (bdc) by similarly sized 2-iodobenzenedicarboxylate (I-bdc) proceeds considerably slower than migration of I-dbc through the UiO-66 crystal. Consequently, the I-bdc is found evenly distributed throughout the UiO-66 samples, even at very short PSE exposure times.
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| 24. |
- Föhlinger, Jens, 1987-, et al.
(författare)
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Self-quenching and Slow Hole Injection May Limit the Efficiency in NiO-based Dye-Sensitized Solar Cells
- 2018
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Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 122:25, s. 13902-13910
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Tidskriftsartikel (refereegranskat)abstract
- A series of bis-tridentate ruthenium complexes was designed to feature opposite localizations of their lowest metal-to-ligand charge transfer (MLCT) excited states, relative to a carboxylic acid that served as a binding group to mesoporous NiO. The purpose was to study the effect of MLCT direction on the rates of hole injection into NiO and subsequent charge recombination. Surprisingly, femtosecond-transient absorption spectroscopy showed that the two heteroleptic, cyclometalated complexes of this series did not inject holes into NiO, but their excited states were nevertheless quenched in a rapid process (on the time scale of hundreds of picoseconds). An identical result was obtained for the dyes on nonreactive ZrO2 and we therefore attribute the short MLCT lifetime to self-quenching, due the high surface concentrations of the dyes. We further show that self-quenching on this time scale can potentially compete with hole injection also for functional NiO sensitizers. A ruthenium polypyridine complex, which has previously been used for NiO-based solar cells, was shown to inject holes only very slowly (τ ≈ 5 ns), in contrast to the common notion that hole injection in dye-NiO systems is ultrafast (predominantly subpicosecond time scale). The hole injection yield was estimated to only ca. 20%, which matches the reported APCE value of the corresponding device [Freys, J. C.; Gardner, J. M.; D’Amario, L.; Brown, A. M.; Hammarström, L. Dalton Trans. 2012, 41, 13105]. Therefore, we suggest that slow injection and self-quenching might be a reason for the low photovoltaic performance of some p-type dye-sensitized solar cells.
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| 25. |
- Gilbert Gatty, Mélina, et al.
(författare)
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Direct evidence of catalyst reduction on dye and catalyst co-sensitized NiO photocathodes by mid-infrared transient absorption spectroscopy
- 2018
-
Ingår i: Chemical Science. - : ROYAL SOC CHEMISTRY. - 2041-6520 .- 2041-6539. ; 9:22, s. 4983-4991
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Tidskriftsartikel (refereegranskat)abstract
- Co-sensitization of molecular dyes and catalysts on semiconductor surfaces is a promising strategy to build photoelectrodes for solar fuel production. In such a photoelectrode, understanding the charge transfer reactions between the molecular dye, catalyst and semiconductor material is key to guide further improvement of their photocatalytic performance. Herein, femtosecond mid-infrared transient absorption spectroscopy is used, for the first time, to probe charge transfer reactions leading to catalyst reduction on co-sensitized nickel oxide (NiO) photocathodes. The NiO films were co-sensitized with a molecular dye and a proton reducing catalyst from the family of [FeFe](bdt)(CO)(6) (bdt = benzene-1,2-dithiolate) complexes. Two dyes were used: an organic push-pull dye denoted E2 with a triarylamine-oligothiophene-dicyanovinyl structure and a coumarin 343 dye. Upon photo-excitation of the dye, a clear spectroscopic signature of the reduced catalyst is observed a few picoseconds after excitation in all co-sensitized NiO films. However, kinetic analysis of the transient absorption signals of the dye and reduced catalyst reveal important mechanistic differences in the first reduction of the catalyst depending on the co-sensitized molecular dye (E2 or C343). While catalyst reduction is preceded by hole injection in NiO in C343-sensitized NiO films, the singly reduced catalyst is formed by direct electron transfer from the excited dye E2* to the catalyst in E2-sensitized NiO films. This change in mechanism also impacts the lifetime of the reduced catalyst, which is only ca. 50 ps in E2-sensitized NiO films but is >5 ns in C343-sensitized NiO films. Finally, the implication of this mechanistic study for the development of better co-sensitized photocathodes is discussed.
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| 26. |
- Glover, Starla D., et al.
(författare)
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Isolating the Effects of the Proton Tunneling Distance on Proton-Coupled Electron Transfer in a Series of Homologous Tyrosine-Base Model Compounds
- 2017
-
Ingår i: Journal of the American Chemical Society. - : AMER CHEMICAL SOC. - 0002-7863 .- 1520-5126. ; 139:5, s. 2090-2101
-
Tidskriftsartikel (refereegranskat)abstract
- The distance dependence of concerted proton-coupled electron transfer (PCET) reactions was probed in a series of three new compounds, where a phenol is covalently bridged by a 5, 6, or 7 membered carbocycle to the quinoline. The carbocycle bridge enforces the change in distance between the phenol oxygen (proton donor) and quinoline nitrogen (proton acceptor), d(O center dot center dot center dot N), giving rise to values ranging from 2.567 to 2.8487 angstrom, and resulting in calculated proton tunneling distances, r(0), that span 0.719 to 1.244 angstrom. Not only does this series significantly extend the range of distances that has been previously accessible for experimental distance dependent PCET studies of synthetic model compounds, but it also greatly improves the isolation of d(O center dot center dot center dot N) as a variable compared to earlier reports. Rates of PCET were determined by time-resolved optical spectroscopy with flash-quench generated [Ru(bpy)(3)](3+) and [Ru(dce)(3)](3+), where bpy = 2,2'-bipyridyl and dce = 4,4'-dicarboxyethylester-2,2'-bipyridyl. The rates increased as d(O center dot center dot center dot N) decreased, as can be expected from a static proton tunneling model. An exponential attenuation of the PCET rate constant was found: k(PCET)(d) = k(PCET)(0)exp[-beta(d-d(0))], with beta similar to 10 angstrom(-1). The observed kinetic isotope effect (KIE = k(H)/k(D)) ranged from 1.2 to 1.4, where the KIE was observed to decrease slightly with increasing d(O center dot center dot center dot N). Both beta and KIE values are significantly smaller than what is predicted by a static proton tunneling model. We conclude that vibrational compression of the tunneling distances, as well as higher vibronic transitions, that contribute to concerted proton coupled electron transfer must also be considered.
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| 27. |
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| 28. |
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| 29. |
- Johnson, Ben A., et al.
(författare)
-
Activating a Low Overpotential CO2 Reduction Mechanism by a Strategic Ligand Modification on a Ruthenium Polypyridyl Catalyst
- 2016
-
Ingår i: Angewandte Chemie International Edition. - : Wiley. - 1433-7851 .- 1521-3773. ; 55:5
-
Tidskriftsartikel (refereegranskat)abstract
- The introduction of a simple methyl substituent on the bipyridine ligand of [Ru(tBu(3)tpy)(bpy)(NCCH3)](2+) (tBu(3)tpy = 4,4',4''-tri-tert-butyl-2,2':6',2''-terpyridine; bpy = 2,2'-bipyridine) gives rise to a highly active electrocatalyst for the reduction of CO2 to CO. The methyl group enables CO2 binding already at the one-electron reduced state of the complex to enter a previously not accessible catalytic cycle that operates at the potential of the first reduction. The complex turns over with a Faradaic efficiency close to unity and at an overpotential that is amongst the lowest ever reported for homogenous CO2 reduction catalysts.
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| 30. |
- Johnson, Ben A., et al.
(författare)
-
Development of a UiO-Type Thin Film Electrocatalysis Platform with Redox-Active Linkers
- 2018
-
Ingår i: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 0002-7863 .- 1520-5126. ; 140:8, s. 2985-2994
-
Tidskriftsartikel (refereegranskat)abstract
- Metal–organic frameworks (MOFs) as electrocatalysis scaffolds are appealing due to the large concentration of catalytic units that can be assembled in three dimensions. To harness the full potential of these materials, charge transport to the redox catalysts within the MOF has to be ensured. Herein, we report the first electroactive MOF with the UiO/PIZOF topology (Zr(dcphOH-NDI)), i.e., one of the most widely used MOFs for catalyst incorporation, by using redox-active naphthalene diimide-based linkers (dcphOH-NDI). Hydroxyl groups were included on the dcphOH-NDI linker to facilitate proton transport through the material. Potentiometric titrations of Zr(dcphOH-NDI) show the proton-responsive behavior via the −OH groups on the linkers and the bridging Zr-μ3-OH of the secondary building units with pKa values of 6.10 and 3.45, respectively. When grown directly onto transparent conductive fluorine-doped tin oxide (FTO), 1 μm thin films of Zr(dcphOH-NDI)@FTO could be achieved. Zr(dcphOH-NDI)@FTO displays reversible electrochromic behavior as a result of the sequential one-electron reductions of the redox-active NDI linkers. Importantly, 97% of the NDI sites are electrochemically active at applied potentials. Charge propagation through the thin film proceeds through a linker-to-linker hopping mechanism that is charge-balanced by electrolyte transport, giving rise to cyclic voltammograms of the thin films that show characteristics of a diffusion-controlled process. The equivalent diffusion coefficient, De, that contains contributions from both phenomena was measured directly by UV/vis spectroelectrochemistry. Using KPF6 as electrolyte, De was determined to be De(KPF6) = (5.4 ± 1.1) × 10–11 cm2 s–1, while an increase in countercation size to n-Bu4N+ led to a significant decrease of De by about 1 order of magnitude (De(n-Bu4NPF6) = (4.0 ± 2.5) × 10–12 cm2 s–1).
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| 31. |
- Johnson, Ben A., et al.
(författare)
-
Electrocatalytic water oxidation by a molecular catalyst incorporated into a metal-organic framework thin film
- 2017
-
Ingår i: Dalton Transactions. - : ROYAL SOC CHEMISTRY. - 1477-9226 .- 1477-9234. ; 46:5, s. 1382-1388
-
Tidskriftsartikel (refereegranskat)abstract
- A molecular water oxidation catalyst, [Ru(tpy)(dcbpy)(OH2)](ClO4)(2) (tpy = 2,2': 6',2''-terpyridine, dcbpy = 2,2'-bipyridine- 5,5'-dicarboxylic acid) [1], has been incorporated into FTO-grown thin films of UiO-67 (UiO = University of Oslo), by post-synthetic ligand exchange. Cyclic voltammograms (0.1 M borate buffer at pH = 8.4) of the resulting UiO67-[RuOH2]@ FTO show a reversible wave associated with the Ru-III/II couple in the anodic scan, followed by a large current response that arises from electrocatalytic water oxidation beyond 1.1 V vs. Ag/AgCl. Water oxidation can be observed at an applied potential of 1.5 V over the timescale of hours with a current density of 11.5 mu A cm(-2). Oxygen evolution was quantified in situ over the course of the experiment, and the Faradaic efficiency was calculated as 82%. Importantly, the molecular integrity of [1] during electrocatalytic water oxidation is maintained even on the timescale of hours under turnover conditions and applied voltage, as evidenced by the persistence of the wave associated with the Ru-III/II couple in the CV. This experiment highlights the capability of metal organic frameworks like UiO-67 to stabilize the molecular structure of catalysts that are prone to form higher clusters in homogenous phase.
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| 32. |
- Johnson, Ben A., et al.
(författare)
-
Judicious Ligand Design in Ruthenium Polypyridyl CO2 Reduction Catalysts to Enhance Reactivity by Steric and Electronic Effects
- 2016
-
Ingår i: Chemistry - A European Journal. - : Wiley. - 0947-6539 .- 1521-3765. ; 22:42, s. 14870-14880
-
Tidskriftsartikel (refereegranskat)abstract
- A series of Ru-II polypyridyl complexes of the structural design [Ru-II(R-tpy)(NN)(CH3CN)](2+) (R-tpy= 2,2': 6', 2''-terpyridine (R= H) or 4,4', 4''-tri-tert-butyl-2,2': 6', 2''-terpyridine (R= tBu); NN= 2,2'-bipyridine with methyl substituents in various positions) have been synthesized and analyzed for their ability to function as electrocatalysts for the reduction of CO2 to CO. Detailed electrochemical analyses establish how substitutions at different ring positions of the bipyridine and terpyridine ligands can have profound electronic and, even more importantly, steric effects that determine the complexes' reactivities. Whereas electron-donating groups para to the heteroatoms exhibit the expected electronic effect, with an increase in turnover frequencies at increased overpotential, the introduction of a methyl group at the ortho position of NN imposes drastic steric effects. Two complexes, [Ru-II(tpy)(6-mbpy)(CH3CN)](2+) (trans-[3](2+); 6-mbpy= 6-methyl- 2,2'-bipyridine) and [Ru-II(tBu-tpy)(6-mbpy)(CH3CN)](2+) (trans-[4](2+)), in which the methyl group of the 6-mbpy ligand is trans to the CH3CN ligand, show electrocatalytic CO2 reduction at a previously unreactive oxidation state of the complex. This low overpotential pathway follows an ECE mechanism (electron transfer-chemical reaction-electron transfer), and is a direct result of steric interactions that facilitate CH3CN ligand dissociation, CO2 coordination, and ultimately catalytic turnover at the first reduction potential of the complexes. All experimental observations are rigorously corroborated by DFT calculations.
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| 33. |
- Kositzki, Ramona, et al.
(författare)
-
Electronic and molecular structure relations in diiron compounds mimicking the [FeFe]-hydrogenase active site studied by X-ray spectroscopy and quantum chemistry
- 2017
-
Ingår i: Dalton Transactions. - : ROYAL SOC CHEMISTRY. - 1477-9226 .- 1477-9234. ; 46:37, s. 12544-12557
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Tidskriftsartikel (refereegranskat)abstract
- Synthetic diiron compounds of the general formula Fe-2(mu-S2R)(CO)(n)(L)(6-n) (R = alkyl or aromatic groups; L = CN- or phosphines) are versatile models for the active-site cofactor of hydrogen turnover in [FeFe]-hydrogenases. A series of 18 diiron compounds, containing mostly a dithiolate bridge and terminal ligands of increasing complexity, was characterized by X-ray absorption and emission spectroscopy in combination with density functional theory. Fe K-edge absorption and K beta main-line emission spectra revealed the varying geometry and the low-spin state of the Fe(I) centers. Good agreement between experimental and calculated core-to-valence-excitation absorption and radiative valence-to-core-decay emission spectra revealed correlations between spectroscopic and structural features and provided access to the electronic configuration. Four main effects on the diiron core were identified, which were preferentially related to variation either of the dithiolate or of the terminal ligands. Alteration of the dithiolate bridge affected mainly the Fe-Fe bond strength, while more potent donor substitution and ligand field asymmetrization changed the metal charge and valence level localization. In contrast, cyanide ligation altered all relevant properties and, in particular, the frontier molecular orbital energies of the diiron core. Mutual benchmarking of experimental and theoretical parameters provides guidelines to verify the electronic properties of related diiron compounds.
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| 34. |
- Kreienbrink, Anika, et al.
(författare)
-
Carbaborane-based alkynylphosphanes and phospholes
- 2015
-
Ingår i: Chemical Communications. - : Royal Society of Chemistry (RSC). - 1359-7345 .- 1364-548X. ; 51:5, s. 836-838
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Tidskriftsartikel (refereegranskat)abstract
- The reaction of 1,2-bis(N,N-dimethylaminochloro-phosphanyl)-1,2-dicarba- closo-dodecaborane(12) and lithiated phenylacetylene gives a five-membered dihydrophosphole derivative with an exocyclic phosphanyl group. This unexpected reaction opens new possibilities for the synthesis of carbaborane-containing phosphorus heterocycles. P, P'-alkynylated 1,2-bis(phosphanyl)-1,2-dicarba-closo-dodecaborane(12)s are obtained from alkynylchlorophosphanes and dilithiated carbaborane. This new class of alkynes can be used for future applications in cyclizations and polymerizations.
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| 35. |
- Layfield, Richard A., et al.
(författare)
-
New Talent : Europe, 2018
- 2018
-
Ingår i: Dalton Transactions. - : Royal Society of Chemistry. - 1477-9226 .- 1477-9234. ; 47:31, s. 10319-10319
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- Welcome to this themed issue of Dalton Transactions entitled New Talent: Europe, 2018 guest edited by Richard A. Layfield, Marinella Mazzanti, Nils Metzler-Nolte and Sascha Ott.
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| 36. |
- Leandri, Valentina, et al.
(författare)
-
Incorporation of a fluorophenylene spacer into a highly efficient organic dye for solid-state dye-sensitized solar cells
- 2016
-
Ingår i: Journal of Photochemistry and Photobiology A. - : Elsevier BV. - 1010-6030 .- 1873-2666. ; 328, s. 59-65
-
Tidskriftsartikel (refereegranskat)abstract
- A new efficient organic dye LEG4F, incorporating a fluorine-substituted phenylene unit in the π-spacer, has been synthesized and tested in dye-sensitized solar cells. Direct comparison with the parent dye LEG4 shows very similar performances in case of liquid electrolyte devices based on iodide/triiodide, yielding a power conversion efficiency of 6.8% under 1 sun and 8.0–8.2% under 0.5 sun illumination. However, LEG4F outperforms its fluorine-free analogue when the liquid electrolyte is replaced by the solid-state hole-transport material Spiro-OMeTAD, reaching 5.3% efficiency compared to 4.8% achieved by LEG4. We show that this improvement is due to the enhancement of the electron lifetime, which reduces recombination at the TiO2/dye/Spiro-OMeTAD interfaces.
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| 37. |
- Leandri, Valentina, et al.
(författare)
-
Rapid Microwave-Assisted Self-Assembly of a Carboxylic-Acid-Terminated Dye on a TiO2 Photoanode
- 2018
-
Ingår i: ACS Applied Energy Materials. - : AMER CHEMICAL SOC. - 2574-0962. ; 1:1, s. 202-210
-
Tidskriftsartikel (refereegranskat)abstract
- Self-assembly of carboxylic-acid-functionalized dyes on mesoporous, anatase TiO2 is at the heart of dye-sensitized solar cells (DSSCs). However, the process often requires 6-20 h of electrode immersion at room temperature in the dye-bath solutions. Here, we introduce a new, rapid microwave-assisted sensitization technique (MINAS), which significantly accelerates the sensitization process and yields high-quality, self-assembled films of an organic dye within 5 min. Targeted experiments show that the effects of the microwave radiation cannot be explained purely on the basis of the thermal component. The interaction of the microwave radiation with the conductive fluorine-doped tin oxide (FTO) electrical contact is a key aspect to consider and a unique feature of MWAS that is the likely cause for producing rapid self-assembly of the dye on the surface.
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| 38. |
- Lissau, Jonas Sandby, et al.
(författare)
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Photon Upconversion from Chemically Bound Triplet Sensitizers and Emitters on Mesoporous ZrO2 : Implications for Solar Energy Conversion
- 2015
-
Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 119:46, s. 25792-25806
-
Tidskriftsartikel (refereegranskat)abstract
- Photon upconversion by sensitized triplet-triplet annihilation (UC-STTA) is studied in systems with triplet sensitizers and emitter molecules cochemisorbed onto nanostructured ZrO2 films. UC-STTA is a promising strategy to overcome the Shockley-Queisser efficiency limit of single-threshold solar cells. The dye-loaded mesoporous ZrO2 films studied herein allow high molecular densities and are good proxy systems for the study of photophysics relevant to dye-sensitized solar cells. Two sensitizer/emitter dye pairs are studied: platinum(II) deuteroporphyrin IX dicarboxylic acid/4,4'-(10-(anthracene-9,10-diyl)dibenzoic acid and platinum(II) deuteroporphyrin IX dimethyl ester/methyl 4-(10-(p-tolyl)anthracen-9-yl)benzoate. Both dye pairs are closely related to the standard UC-STTA molecular pair platinum(II) octaethylporphyrin (PtOEP)/9,10-diphenylanthracene (DPA). By chemically anchoring the upconverting dye pairs onto ZrO2 films a significant improvement in UC-STTA efficiency is achieved with respect to previously studied cophysisorbed PtOEP/DPA. Controlled variation of the sensitizer/emitter dye ratios onto the surface shows that new energy loss mechanisms appear at high sensitizer surface coverage. Spectral signatures of porphyrin aggregates suggest separate sensitizer domains form, which limits the triplet sensitization of emitter molecules. The nanosecond time scale rise and decay of the observed UC emission are likely linked to the sample stability over time; UC emission is observed 1 year after sample preparation. These are promising properties for the application of this type of system for solar energy conversion.
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| 39. |
- Lissau, Jonas Sandby, et al.
(författare)
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What Limits Photon Upconversion on Mesoporous Thin Films Sensitized by Solution-Phase Absorbers?
- 2015
-
Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 119:9, s. 4550-4564
-
Tidskriftsartikel (refereegranskat)abstract
- Photon upconversion by sensitized triplet-triplet annihilation (UC-STTA) is a promising strategy for breaking the Shockley-Queisser limit for efficiency of single-threshold solar cells, and in particular dye-sensitized solar cells (DSSCs). Here, we report on a heterogeneous UC system, where the annihilating dyes (emitters) are bound to a ZrO2 nanostructured film and the light absorbing dyes (sensitizers) are free in solution. A comparative study of four different emitter dyes was conducted, all of them derivatives of the well-known UC-STTA emitter dye 9,10-diphenylanthracene (DPA), and in every case, the sensitizer dye was platinum(II) octaethylporphyrin (PtOEP). The physical separation of emitter and sensitizer molecules in two different phases makes homogeneous triplet-triplet annihilation among sensitizers in solution a significant loss channel at high excitation intensity and low emitter surface coverage. For the studied emitter dyes, the number and type of anchor groups, and the solubility of the emitter dye in the employed solvents, are the determining factors of the UC output. The signal evolves in time and with light exposure due to emitter desorption and light-induced endoperoxide formation. These results can guide the way toward a better understanding of UC-STTA on nanocrystalline metal oxides and its development for solar energy applications.
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| 40. |
- Liu, Tianfei, et al.
(författare)
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Accelerating proton-coupled electron transfer of metal hydrides in catalyst model reactions
- 2018
-
Ingår i: Nature Chemistry. - : Springer Science and Business Media LLC. - 1755-4330 .- 1755-4349. ; 10:8, s. 881-887
-
Tidskriftsartikel (refereegranskat)abstract
- 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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| 41. |
- Liu, Tianfei, et al.
(författare)
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Elucidating Proton-Coupled Electron Transfer Mechanisms of Metal Hydrides with Free Energy- and Pressure-Dependent Kinetics
- 2019
-
Ingår i: Journal of the American Chemical Society. - : AMER CHEMICAL SOC. - 0002-7863 .- 1520-5126. ; 141:43, s. 17245-17259
-
Tidskriftsartikel (refereegranskat)abstract
- Proton-coupled electron transfer (PCET) was studied in a series of tungsten hydride complexes with pendant pyridyl arms ([(PyCH2Cp)WH(CO)(3)], PyCH2Cp = pyridyl methyl cyclopentadienyl), triggered by laser flash-generated Ru-III-tris-bipyridine oxidants, in acetonitrile solution. The free energy dependence of the rate constant and the kinetic isotope effects (KIEs) showed that the PCET mechanism could be switched between concerted and the two stepwise PCET mechanisms (electron-first or proton-first) in a predictable fashion. Straightforward and general guidelines for how the relative rates of the different mechanisms depend on oxidant and base are presented. The rate of the concerted reaction should depend symmetrically on changes in oxidant and base strength, that is on the overall Delta G(PCET)(0), and we argue that an "asynchronous" behavior would not be consistent with a model where the electron and proton tunnel from a common transition state. The observed rate constants and KIEs were examined as a function of hydrostatic pressure (1-2000 bar) and were found to exhibit qualitatively different dependence on pressure for different PCET mechanisms. This is discussed in terms of different volume profiles of the PCET mechanisms as well as enhanced proton tunneling for the concerted mechanism. The results allowed for assignment of the main mechanism operating in the different cases, which is one of the critical questions in PCET research. They also show how the rate of a PCET reaction will be affected very differently by changes of oxidant and base strength, depending on which mechanism dominates. This is of fundamental interest as well as of practical importance for rational design of, for example, catalysts for fuel cells and solar fuel formation, which operate in steps of PCET reactions. The mechanistic richness shown by this system illustrates that the specific mechanism is not intrinsic to a specific synthetic catalyst or enzyme active site but depends on the reaction conditions.
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| 42. |
- Lomoth, Reiner, et al.
(författare)
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Probing the elementary steps of PCET catalysis
- 2018
-
Ingår i: Abstracts of Papers of the American Chemical Society. - Washington, D.C. : American Chemical Society (ACS). - 0065-7727. ; 255
-
Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)
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| 43. |
- Mahanti, Bani, et al.
(författare)
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Homogeneous Water Oxidation by Half-Sandwich Iridium(III) N-Heterocyclic Carbene Complexes with Pendant Hydroxy and Amino Groups
- 2017
-
Ingår i: ChemSusChem. - : Wiley. - 1864-5631 .- 1864-564X. ; 10:22, s. 4616-4623
-
Tidskriftsartikel (refereegranskat)abstract
- Herein, we report three (IrCp)-Cp-III* complexes with hydroxy-or amino-functionalized N-heterocyclic carbene (NHC) ligands that catalyze efficient water oxidation induced by addition of ceric ammonium nitrate (CAN). The pendant hydroxy or amino groups are very important for activity, and the complexes with heteroatom-functionalized NHC ligands show up to 15 times higher rates of oxygen evolution in CAN-induced water oxidation than a reference (IrCp)-Cp-III* complex without heteroatom functionalization. The formation of molecular high-valent Ir intermediates that are presumably involved in the rate-determining step for water oxidation is established by UV/Vis spectroscopy and ESI-MS under turnover conditions. The hydroxy groups on the NHC ligands, as well as chloride ligands on the iridium center are proposed to structurally stabilize the highvalent species, and thereby improve the catalytic activity. The Ir-III complex with a hydroxy-functionalized NHC shows the highest catalytic activity with a TON of 2500 obtained in 3 h and with >90% yield relative to the amount of oxidant used.
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| 44. |
- Mai, Juri
(författare)
-
Bridging McMurry and Wittig in One-Pot : Olefins from Stereoselective, Reductive Couplings of Two Aldehydes via Phosphaalkenes
- 2019
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The formation of C=C bonds is of great importance for fundamental and industrial synthetic organic chemistry. There are many different methodologies for the construction of C=C bonds in the literature, but currently only the McMurry reaction allows the reductive coupling of two carbonyl compounds to form alkenes. This thesis contributes to the field of carbonyl olefinations and presents the development of a new synthetic protocol for a one-pot reductive coupling of two aldehydes to alkenes based on organophosphorus chemistry. The coupling reagent, a phosphanylphosphonate, reacts with an aldehyde to yield a phosphaalkene intermediate which upon activation with a base undergoes an olefination with a second aldehyde.A general overview of synthetic methods for carbonyl olefinations and the chemistry of phosphaalkenes is given in the background chapter. The Wittig reaction and its variations are discussed in detail. The synthesis, reactivity, properties and applications of phosphaalkenes are highlighted with particular focus on strategies to stabilize these otherwise reactive species.The third chapter describes a novel method for the reductive coupling of aldehydes. The activation of phosphaalkene intermediates by a hydroxide base, mechanistic studies, development of a one-pot procedure and investigations of the substrate scope are discussed. The new one-pot reaction is advantageous over the McMurry coupling since it allows the formation of unsymmetrical E-alkenes under mild conditions.The next chapter is dedicated to a modification of the reaction sequence. The results show that activation of the phosphaalkene with an alkoxide instead of hydroxide, followed by oxidation, generates a more reactive transient species that can undergo the coupling with electron rich (deactivated) aldehydes which was not possible under the initial reaction conditions.Chapter five describes a modification of the phosphanylphosphonate reagent that enables the preparation of alkenes with high Z-stereoselectivity.In the final chapter, chemical equilibria studies of triphenylphosphaalkenes are presented. It is found that phosphaalkenes with poor kinetic stabilization can also be used as intermediates in the carbonyl-to-alkene coupling chemistry.In summary, this thesis presents the development of an unprecedented synthetic method for the direct formation of C=C double bonds from two aldehydes together with strategies on improvements of the substrate scope and modifications to control the stereochemical outcome of the reaction.
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| 45. |
- Mai, Juri, et al.
(författare)
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Reductive coupling of two aldehydes to unsymmetrical E-alkenes via phosphaalkene and phosphinate intermediates
- 2018
-
Ingår i: Chemical Communications. - : Royal Society of Chemistry (RSC). - 1359-7345 .- 1364-548X. ; 54:52, s. 7163-7166
-
Tidskriftsartikel (refereegranskat)abstract
- Stilbenes with push-pull electronics are directly accessible from an electron-rich and an electron-deficient benzaldehyde in a novel reductive aldehyde cross-coupling reaction. The one-pot procedure is enabled by the oxidation of a transient phosphinite to the corresponding phosphinate which exhibits sufficient reactivity towards deactivated aldehydes.
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| 46. |
- Mai, Juri, et al.
(författare)
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The Fascinating World of Phosphanylphosphonates : From Acetylenic Phosphaalkenes to Reductive Aldehyde Couplings
- 2019
-
Ingår i: Synlett. - : Georg Thieme Verlag KG. - 0936-5214 .- 1437-2096. ; 30:16, s. 1867-1885
-
Tidskriftsartikel (refereegranskat)abstract
- This account highlights the versatility of phosphanylphosphonates, which can be used for the preparation of phosphorus-containing π-systems and as reagents for the reductive coupling of carbonyl compounds to alkenes. Phosphanylphosphonates with metal fragments coordinated to the P-lone pair have been known for a long time and they have been used for the synthesis of phosphaalkenes by means of the phospha-Horner–Wadsworth–Emmons reaction. With the original aim of incorporating phosphorus heteroatoms into classical all-carbon ethynylethene scaffolds, we entered the field of phosphanylphosphonates with the discovery that these compounds engage in complex cascade reactions with acetylenic ketones, forming 1,2-oxaphospholes, cumulenes, and bisphospholes. Later, we synthesized the first metal-free phosphanylphosphonate, which reacts with aldehydes to yield phosphaalkenes, but gives phospholones when diacetylenic ketones are used as substrates. In the final part of the account, we outline our discovery and the development of an unprecedented carbonyl–carbonyl cross-coupling reaction. This protocol offers a straightforward method for the synthesis of nonsymmetric 1,2-disubstituted alkenes directly from two dissimilar aldehydes.1. Combining Acetylenes with Phosphaalkenes2. Synthetic Examples of Acetylenic Phosphaalkenes3. The Phospha-Horner–Wadsworth–Emmons Approach to Phosphaalkenes3.1. Metal-Coordinated Phosphanylphosphonates3.2. Mechanism of the Phospha-Horner–Wadsworth–Emmons Reaction3.3. The First Metal-Free Phosphanylphosphonate and Its Reactivity with Aldehydes4. Reactions with Acetylenic Ketones4.1. Metal-Coordinated Phosphanylphosphonate and Monoacetylenic Ketones4.2. Metal-Coordinated Phosphanylphosphonate and Diacetylenic Ketones4.3. Metal-Free Phosphanylphosphonate and Diacetylenic Ketones5. Metal-Free Phosphanylphosphonate as a Coupling Reagent for Aldehydes6. E-Alkenes by the Reductive Coupling of Two Aldehydes7. Conclusions and Outlook
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| 47. |
- McCarthy, Brian D., et al.
(författare)
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Facile Orientational Control of M2L2P SURMOFs on < 100 > Silicon Substrates and Growth Mechanism Insights for Defective MOFs
- 2019
-
Ingår i: ACS Applied Materials and Interfaces. - : American Chemical Society (ACS). - 1944-8244 .- 1944-8252. ; 11:41, s. 38294-38302
-
Tidskriftsartikel (refereegranskat)abstract
- Layer-by-layer growth of Cu-2(bdc)(2)(dabco) surface-mounted metal organic frameworks (SURMOFs) was investigated on silicon wafers treated with different surface anchoring molecules. Well-oriented growth along the [100] and [001] directions could be achieved with simple protocols: growth along the [100] direction was achieved by substrate pretreatment with 80 degrees C piranha, while growth along the [001] direction was enabled by only rinsing silicon with absolute ethanol. Growth along the [001] direction produced more homogeneous SURMOF films. Optimization to enhance [001]-preferred orientation growth revealed that small changes in the SURMOF growth sequence (the number of rinse steps and linker concentrations) have a noticeable impact on the final film quality and the number of misaligned crystals. This new straightforward protocol was used to successfully grow other layer pillar-type SURMOFs, including the growth of Cu-2(bdc)(2)(bipy) with simultaneous suppression of framework interpenetration.
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| 48. |
- Mijangos, Edgar, et al.
(författare)
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Evaluation of two- and three-dimensional electrode platforms for the electrochemical characterization of organometallic catalysts incorporated in non-conducting metal-organic frameworks
- 2017
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Ingår i: Dalton Transactions. - : ROYAL SOC CHEMISTRY. - 1477-9226 .- 1477-9234. ; 46:15, s. 4907-4911
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Tidskriftsartikel (refereegranskat)abstract
- The development of a reliable platform for the electrochemical characterization of a redox-active molecular diiron complex, [FeFe], immobilized in a non-conducting metal organic framework (MOF), UiO-66, based on glassy-carbon electrodes is reported. Voltammetric data with appreciable current responses can be obtained by the use of multiwalled carbon nanotubes (MWCNT) or mesoporous carbon (CB) additives that function as conductive scaffolds to interface the MOF crystals in "three-dimensional" electrodes. In the investigated UiO-66-[FeFe] sample, the low abundance of [FeFe] in the MOF and the intrinsic insulating properties of UiO-66 prevent charge transport through the framework, and consequently, only [FeFe] units that are in direct physical contact with the electrode material are electrochemically addressable.
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- Mirmohades, Mohammad, 1986-
(författare)
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Insight into Catalytic Intermediates Relevant for Water Splitting
- 2016
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Catalysis is an important part of chemistry. This is also reflected in the chemical industry where 85-90 % of all products are made catalytically. Also nature employs catalysts, i.e. enzymes, for its reactions.To improve on the already existing catalysts one can learn a lot from nature which often uses earth-abundant elements in the enzymes which have also been optimized and finely tuned for billions of years. To gain a deeper understanding of both enzymatic and artificial catalysis one needs to investigate the mechanism of the catalytic process. But for very efficient catalysts with turnover frequencies of several thousand per second this is not easy, since an investigation of the mechanism involves resolving intermediates in the catalytic cycle. The intermediates in these instances are short-lived corresponding to their turnover frequencies. A maximum turnover frequency of 1,000 s-1 e.g. means that each catalyst goes through the whole catalytic cycle in 1 ms. Therefore time-resolved techniques are necessary that have a faster detection speed than the turnover frequency of the catalyst.Flash photolysis is a spectroscopic technique with an instrument response function down to 10 ns. Coupling this technique with mid-infrared probing yields an excellent detection system for probing different redox and protonation states of carbonyl metal complexes. Since many catalysts as well as natural enzymes involved in water splitting are metal carbonyl complexes this is an ideal technique to monitor the intermediates of these catalysts.Chapter 3 covers the investigation of [FeFe] hydrogenases, enzymes that catalyze the reduction of protons to hydrogen in nature. Chapter 4 investigates the intermediates of biomimetic complexes, resembling the active site of natural [FeFe] hydrogenases. Chapter 5 covers the insights gained from investigating other catalysts which are also involved in water splitting and artificial photosynthesis.
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