| 1. |
- Wang, Ying, et al.
(författare)
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Asymmetric oxidation of sulfides with H2O2 catalyzed by titanium complexes of Schiff bases bearing a dicumenyl salicylidenyl unit
- 2011
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Ingår i: Applied organometallic chemistry. - : Wiley. - 0268-2605 .- 1099-0739. ; 25:5, s. 325-330
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Tidskriftsartikel (refereegranskat)abstract
- The sterically hindered Schiff bases (L-3-L-5), prepared from 3,5-dicumenyl salicylaldehyde and chiral amino alcohols, were used in combination with Ti(OiPr)(4) for asymmetric oxidation of aryl methyl sulfides with H2O2 as terminal oxidant. Among the ligands L-3-L-5, L-4 with a tert-butyl group in the chiral carbon of the amino alcohol moiety gave the best result with 89% yield and 73% ee for the sulfoxidation of thioanisole under optimal conditions [with 1 mol% of Ti(OiPr)(4) in a molar ratio of 100 : 1 : 1.2 : 120 for sulfide : Ti(OiPr)(4) : ligand : H2O2 in CH2Cl2 at 0 degrees C for 3 h]. The reaction afforded good yield (84%) with a moderate enantioselectivity (62% ee) even with a lower catalyst loading from 1.0 to 0.5 mol%. The oxidations of methyl 4-bromophenyl sulfide and methyl 4-methoxyphenyl sulfide with H2O2 catalyzed by the Ti(OiPr)(4)-L-4 system gave 79-84% yieldsand54-59% ee of the corresponding sulfoxides in CH2Cl2 at 20 degrees C. The chiral induction capability of the cumenyl-modified sterically hindered Schiff bases for sulfoxidation was compared with the conventional Schiff bases bearing tert-butyl groups at the 3,5-positions of the salicylidenyl unit.
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| 2. |
- Wang, Ying, et al.
(författare)
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Highly enantioselective sulfoxidation with vanadium catalysts of Schiff bases derived from bromo- and iodo-functionalized hydroxynaphthaldehydes
- 2010
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Ingår i: Journal of Catalysis. - : Elsevier BV. - 0021-9517 .- 1090-2694. ; 273:2, s. 177-181
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Tidskriftsartikel (refereegranskat)abstract
- Two series of chiral Schiff bases, 4a-e and 5a-e, prepared from the condensation of the mono-, di-, trib-romohydroxynaphthaldehyde or monoiodohydroxynaphthaldehyde with chiral amino alcohols, were used in combination with VO(acac)(2) for the asymmetric oxidation of aryl methyl sulfides using H2O2 as terminal oxidant. Among these Schiff bases, dibromo-functionalized 4d and iodo-functionalized 5e gave high yields (91-93%) with good enantioselectivities (80-82% ee) for the oxidation of thioanisole in dichloromethane. The asymmetric oxidation of thioanisole in toluene using these Schiff bases gave methyl phenyl sulfoxide in satisfactory isolated yields (48-62%) with high enantioselectivities (91-94% ee), which were further improved by a modified procedure with the ee value up to 98% in 62% yield. The oxidations of other aryl methyl sulfides in toluene with dibromo- and iodo-functionalized Schiff bases 5d and 5e as ligands using the modified procedure afforded the corresponding sulfoxides in 55-67% isolated yields with 95-99% ee. (C) 2010 Elsevier Inc. All rights reserved.
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| 3. |
- Wang, Dongping, et al.
(författare)
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Asymmetric epoxidation of styrene and chromenes catalysed by dimeric chiral (pyrrolidine salen)Mn(III) complexes
- 2006
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Ingår i: Applied Catalysis A. - : Elsevier BV. - 0926-860X .- 1873-3875. ; 315, s. 120-127
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Tidskriftsartikel (refereegranskat)abstract
- Two dimeric chiral (pyrrolidine salen)Mn(III) complexes 3 and 4 were prepared, in which the two (pyrrolidine salen)Mn(III) units are linked either by a p-xylylene or by ap-phthalyl bridge. High yields were attained for asymmetric epoxidation of styrene and substituted chromenes at 0.5-4.0 mol% catalyst loading of 3 and 4 using NaClO/PPNO and m-CPBA/NMO as oxidant systems, with 37-39% ee for styrene and 86-95% ee for substituted chromenes. Dimeric complexes 3 and 4 displayed higher activities than their parent monomeric complexes 1 and 2 of double equiv for epoxidation of substituted chromenes. Complex 3 bearing two tertiary amine units displayed considerably higher activity than analogous dimeric complex 4 containing two carboxamide units in the aforementioned reaction. The effect of excess CH3I on the epoxidation of 6-nitro-2,2-dimethylchromene catalysed by 3 in the aqueous/organic biphasic medium was explored. The recovery and recycling possibilities of the dimeric complexes 3 and 4 were studied.
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| 4. |
- Wang, Dongping, et al.
(författare)
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Influence of the built-in pyridinium salt on asymmetric epoxidation of substituted chromenes catalysed by chiral (pyrrolidine salen)Mn(III) complexes
- 2007
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Ingår i: Journal of Molecular Catalysis A. - : Elsevier BV. - 1381-1169 .- 1873-314X. ; 270:02-jan, s. 278-283
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Tidskriftsartikel (refereegranskat)abstract
- Chiral (pyrrolidine salen)Mn(III) complexes 1 with an N-benzoyl group and 2 with an N-isonicotinoyl group as well as the corresponding N-methyl (3) and N-benzyl (4) pyridinium salts of 2 were synthesized. The catalytic properties of 1-4 and 2 with excess CH3I were explored to figure out the influence of the internal pyridinium salt in the catalyst on asymmetric epoxidation of substituted chromenes with NaClO/PPNO as an oxidant system in the aqueous/organic biphasic medium. The (pyrrolidine salen)Mn(III) complexes with an internal pyridinium salt, either formed in situ or isolated, displayed higher activities than analogous complexes 1, 2 and Jacobsen's catalyst in the aforementioned reaction, with comparable high yields and ee values. The acceleration of the reaction rate is attributed to the phase transfer capability of the built-in pyridinium salt of the (salen)Mn(III) catalyst. The effect of the internal pyridinium salt on the epoxidation of substituted chromenes is similar to that of the external pyridinium salts and ammonium halides.
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| 5. |
- Deng, Zijian, et al.
(författare)
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Helical Copper Redox Mediator with Low Electron Recombination for Dye-Sensitized Solar Cells
- 2021
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Ingår i: ACS Sustainable Chemistry and Engineering. - : American Chemical Society (ACS). - 2168-0485. ; 9:15, s. 5252-5259
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Tidskriftsartikel (refereegranskat)abstract
- Redox mediators play a major role in determining the photocurrent and photovoltage in dye-sensitized solar cells (DSSCs). Copper complexes are a good option for redox mediators but suffer from electron recombination. The traditional method is to add 4-(tert-butyl)pyridine (TBP) to the electrolyte, which is coordinated with the empty orbit of Ti, thereby slowing down the oxidized mediator's ability to capture electrons. However, this strategy will result in competitive coordination between the redox mediator and TBP, decreasing the stability of the device. In this study, two helical copper(I) complexes are synthesized and applied to TBP-free solar cells. La (1,3-bis(2,2'-bipyridin-6-yloxy)propane) and Lb (1,3-bis[(6'-methyl-2,2'-bipyridin-6-yl)oxy]propane) tend to form double-stranded helicates ([Cu-2(Ln)(2)](2+), n = a, b) rather than mononuclear complexes ([Cu(Ln)](+), n = a, b). To facilitate quantitative analysis of the complexes, Cu(I)Ln and Cu(II)Ln (n = a, b) are used as molecular formulae. (CuLa)-La-I and Cu(I)Lb are characterized by electrospray mass spectroscopy, H-1 NMR spectroscopy, and electrochemistry. J-V measurement shows that both V-oc and J(sc) increase with the increase of (CuLa)-La-I concentration (below 0.1 M), and the best power conversion efficiency is 8.2%. The relationship between Cu(I) concentration and recombination for further study was measured by IMVS.
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| 6. |
- Li, Xueqiang, et al.
(författare)
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Photocatalytic Water Reduction and Study of the Formation of FeIFe0 Species in Diiron Catalyst Sytems
- 2012
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Ingår i: ChemSusChem. - : Wiley. - 1864-5631. ; 5:5, s. 913-919
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Tidskriftsartikel (refereegranskat)abstract
- Noble-metal-free systems with bio-inspired diiron dithiolate mimics of the [FeFe]-hydrogenase active site, namely, [(mu-pdt)Fe2(CO)5L] [pdt=propanedithiolate; L=P(CH2OH)3 (1), P(CH3)3 (2)], as water reduction catalysts with xanthene dyes as photosensitizers and triethylamine as a sacrificial electron donor were studied for visible-light-driven water reduction to hydrogen. These systems display good catalytic activities with the efficiencies in hydrogen evolution of up to 226 turnovers for 1, if Eosin Y was used as the photosensitizer in an environmentally benign solvent (EtOH/H2O) after 15 h of irradiation (?>450 nm) under optimal conditions. Under all of the conditions adopted, 1 that has a water soluble phosphine ligand, P(CH2OH)3 displayed a higher efficiency than 2, which bears a PMe3 ligand. The photoinduced electron transfer in the systems was studied using fluorescence, transient absorption, time-resolved UV/Vis, and in situ electron paramagnetic resonance (EPR) spectroscopy. A new electron-transfer mechanism is proposed for hydrogen evolution by these iron-based photocatalytic systems.
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| 7. |
- Song, Xinkai, et al.
(författare)
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Improving energy transfer efficiency of dye-sensitized solar cell by fine tuning of dye planarity
- 2019
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Ingår i: Solar Energy. - : Elsevier. - 0038-092X .- 1471-1257. ; 187, s. 274-280
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Tidskriftsartikel (refereegranskat)abstract
- Two push-pull metal-free sensitizers with 5,11-dihydroindolo[3,2-b]carbazole derivatives as electron-donating groups and 4-(benzo[c][1,2,5]thiadiazol-4-ylethynyl)benzoic acid (BTZ) as electron-withdrawing unit, denoted by SK201 and SK202, were synthesized and used for fabrication of dye-sensitized solar cells (DSSCs). SK202 contains a thienyl group between the donor and acceptor, whereas in SK201 the donor and acceptor are connected directly by a single bond. Introduction of a thienyl group improved the planarity of the dye molecule, broadened the absorption spectrum, enhanced the molar extinction coefficient, increased the dye loading on TiO2, and accelerated interface electron transfer on TiO2. This fine tuning of dye structure improved the performances of DSSCs based on SK202 sensitizers and gave a power conversion efficiency (PCE) of 11.0% (J(SC) 16.5 mA cm(-2), V-OC 932 mV, and fill factor 71.7%), compared with that of 7.2% for SK201, under standard AM1.5G solar irradiation (100 mW cm(-2)) with a Co(II/III) complex based redox couple.
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| 8. |
- Tan, Qin, et al.
(författare)
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Application of Small Molecule Donor Materials Based on Phenothiazine Core Unit in Bulk Heterojunction Solar Cells
- 2014
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Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 118:30, s. 16851-16855
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Tidskriftsartikel (refereegranskat)abstract
- A D-pi-A type small molecule PTZ1 and an A-pi-D-pi-A type small molecule PTZ2 with phenothiazine as the central building block and dicyanovinyl as the electron-withdrawing end-group have been designed and synthesized. Compared with D-pi-A type donor material PTZ1, the donor material PTZ2 with A-pi-D-pi-A configuration shows much wider response to solar light. The donor material PTZ1 possesses more positive highest occupied molecular orbital level, and higher V obtained for devices with PTZ1/PC71BM blend as the active layer. An improved efficiency of 3.25% was obtained for the PTZ2/PC71BM based solar cells.
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| 9. |
- Wang, Lei, et al.
(författare)
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Efficient Organic Sensitizers with Pyridine-N-oxide as an Anchor Group for Dye-Sensitized Solar Cells
- 2014
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Ingår i: ChemSusChem. - : Wiley. - 1864-5631 .- 1864-564X. ; 7:9, s. 2640-2646
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Tidskriftsartikel (refereegranskat)abstract
- Five organic dyes with pyridine-N-oxide as the anchor group and electron acceptor have been synthesized and applied in dye-sensitized solar cells (DSSCs). Benzothiadiazole was introduced in the conjugation system to increase the electron withdrawing properties, FTIR spectra showed that the coordination was between the pyridine-N-oxide and the Bronsted acid site on the TiO2 surface. The relationship between different dye structures and the performance of the DSSCs was investigated systematically. The location of the thiophene unit was studied, and the direct linkage of benzothiadiazole with pyridine-Noxide was beneficial to broaden the absorption. The donor-acceptor-acceptor-configured dye WL307, which has 2-ethylhexyloxy chains in the donor part, showed the best efficiency of 6.08% under 100 mWcm(-2) light illumination. The dye series showed a fairly good stability during the one month test period.
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| 10. |
- Wang, Lei, et al.
(författare)
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Novel organic dyes with anchoring group of quinoxaline-2, 3-diol and the application in dye-sensitized solar cells
- 2015
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Ingår i: Dyes and pigments. - : Elsevier BV. - 0143-7208 .- 1873-3743. ; 113, s. 581-587
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Tidskriftsartikel (refereegranskat)abstract
- Two organic quinoxaline dyes (WQ-1 and WQ-2) with a structure of quinoxaline-2, 3-diol as the electron withdrawing and anchoring group were synthesized and applied in the dye-sensitized solar cells. Fourier transform infrared spectroscopy and two other reference dyes (WQ-R1 and WQ-R2) without the hydroxyl groups were introduced to ascertain the adsorption properties of the dye series. The effect of the new electron acceptor and anchoring group on the performance of solar cells was investigated systematically. Under the standard light illumination (100 mW m(-2)), WQ-2 got an efficiency of 2.25%, with a short circuit photocurrent density of 5.51 mA cm(-2), an open circuit voltage of 0.612 V and a fill factor of 66.74%.
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