| 1. |
- Bhunia, Asamanjoy, et al.
(författare)
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A photoluminescent covalent triazine framework : CO2 adsorption, light-driven hydrogen evolution and sensing of nitroaromatics
- 2016
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Ingår i: Journal of Materials Chemistry A. - : Royal Society of Chemistry (RSC). - 2050-7488 .- 2050-7496. ; 4:35, s. 13450-13457
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Tidskriftsartikel (refereegranskat)abstract
- A highly photoluminescent (PL) porous covalent triazine-based framework (PCTF-8) is synthesized from tetra(4-cyanophenyl) ethylene by using trifluoromethanesulfonic acid as the catalyst at room temperature. Due to triazine units in the framework, the PCTF-8 exhibits excellent thermal stability (>400 degrees C). The Brunauer-Emmett-Teller (BET) specific surface area of PCTF-8 is 625 m(2) g(-1) which is lower than the one obtained from the synthesis under Lewis acid conditions (ZnCl2). At 1 bar and 273 K, the PCTF-8 adsorbs a significant amount of CO2 (56 cm(3) g(-1)) and CH4 (17 cm(3) g(-1)) which is highly comparable to nanoporous 1,3,5-triazine frameworks (NOP-1-6, 29-56 cm(3) g(-1)). This nitrogen rich framework exhibits good ideal selectivity (61 : 1 (85% N-2 : 15% CO2) at 273 K, 1 bar). Thus, it can be used as a promising candidate for potential applications in post-combustion CO2 capture and sequestration technologies. In addition, photoluminescence properties as well as the sensing behaviour towards nitroaromatics have been demonstrated. The fluorescence emission intensity of PCTF-8 is quenched by ca. 71% in the presence of 2,4,6-trinitrophenol (TNP). From time-resolved studies, a static quenching behaviour was found. This high photoluminescence property is used for hydrogen evolving organic photocatalysis from water in the presence of a sacrificial electron donor and a cocatalyst.
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| 2. |
- Bowring, Miriam A., et al.
(författare)
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Activationless Multiple-Site Concerted Proton-Electron Tunneling
- 2018
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Ingår i: Journal of the American Chemical Society. - : AMER CHEMICAL SOC. - 0002-7863 .- 1520-5126. ; 140:24, s. 7449-7452
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Tidskriftsartikel (refereegranskat)abstract
- The transfer of protons and electrons is key to energy conversion and storage, from photosynthesis to fuel cells. Increased understanding and control of these processes are needed. A new anthracene-phenol-pyridine molecular triad was designed to undergo fast photo-induced multiple-site concerted proton-electron transfer (MS-CPET), with the phenol moiety transferring an electron to the photoexcited anthracene and a proton to the pyridine. Fluorescence quenching and transient absorption experiments in solutions and glasses show rapid MS-CPET (3.2 X 10(10) s(-1) at 298 K). From 5.5 to 90 K, the reaction rate and kinetic isotope effect (KIE) are independent of temperature, with zero Arrhenius activation energy. From 145 to 350 K, there are only slight changes with temperature. This MS-CPET reaction thus occurs by tunneling of both the proton and electron, in different directions. Since the reaction proceeds without significant thermal activation energy, the rate constant indicates the magnitude of the electron/proton double tunneling probability.
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| 3. |
- 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
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Ingår i: Journal of the American Chemical Society. - : AMER CHEMICAL SOC. - 0002-7863 .- 1520-5126. ; 141:43, s. 17245-17259
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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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| 4. |
- Pati, Palas Baran, et al.
(författare)
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Insights into the Mechanism of a Covalently Linked Organic Dye-Cobaloxime Catalyst System for Dye-Sensitized Solar Fuel Devices
- 2017
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Ingår i: ChemSusChem. - : Wiley. - 1864-5631 .- 1864-564X. ; 10:11, s. 2480-2495
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Tidskriftsartikel (refereegranskat)abstract
- A covalently-linked organic dye-cobaloxime catalyst system is developed by facile click reaction for mechanistic studies and application in a dye sensitized solar fuel device based on mesoporous NiO. This system has been systematically investigated by photophysical measurements, density functional theory, time resolved fluorescence, transient absorption spectroscopy as well as photoelectron spectroscopy. The results show that irradiation of the dye-catalyst on NiO leads to ultrafast hole injection into NiO from the excited dye, followed by a fast electron transfer to reduce the catalyst unit. Moreover, they suggest that the dye undergoes structural changes in the excited state and that excitation energy transfer occurs between neighboring molecules. The photoelectrochemical experiments also show the hydrogen production by this system-based NiO photocathode. The axial chloride ligands of the catalyst are released during photocatalysis to create the active sites for proton reduction. A working mechanism of the dye-catalyst on photocathode is eventually proposed on the basis of this study.
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| 5. |
- Sucre-Rosales, Estefania, et al.
(författare)
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Solvatochromism and intramolecular charge transfer in dialkylamino- substituted halogenated thienyl chalcone analogues
- 2020
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Ingår i: Chemical Physics. - : Elsevier BV. - 0301-0104 .- 1873-4421. ; 537
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Tidskriftsartikel (refereegranskat)abstract
- Herein, we present the study of two complementary intramolecular charge transfer (ICT) transitions in two sets of dialkylamino-substituted halogenated thienyl chalcones. We demonstrate that while the first (and stronger) ICT takes place from the 4-(dialkylamino)phenyl moiety to the enone, the second ICT involves the thienyl substituent as the donor. The former is evidenced by a robust solvatochromic shift in both absorption and emission spectra, implying a large increase in the dipole moment upon excitation to the lowest excited state. The latter, a short-range ICT process, is confirmed upon photoexcitation of the higher energy bands, and its enhancement by the larger polarizability of the iodine substituent. With the help of (TD)-DFT calculations and the solvatochromic method, we quantified the extent of these effects and set the stage for further developments towards the design of new chalcone-based dyes. We demonstrated that theoretical calculations allow fine-tuning the sensitive balance between these complementary ICT processes.
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| 6. |
- Wang, Lei, et al.
(författare)
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Organic Polymer Dots as Photocatalysts for Visible Light-Driven Hydrogen Generation
- 2016
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Ingår i: Angewandte Chemie International Edition. - : Wiley. - 1433-7851 .- 1521-3773. ; 55:40, s. 12306-12310
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Tidskriftsartikel (refereegranskat)abstract
- For the first time, organic semiconducting polymer dots (Pdots) based on poly[(9,9'-dioctylfluorenyl-2,7-diyl)-co-(1,4-benzo-{2,1', 3} thiadiazole)] (PFBT) and polystyrene grafting with carboxyl-group-functionalized ethylene oxide (PS-PEG-COOH) are introduced as a photocatalyst towards visible-light-driven hydrogen generation in a completely organic solvent-free system. With these organic Pdots as the photocatalyst, an impressive initial rate constant of 8.3 mmol h(-1) g(-1) was obtained for visible-light-driven hydrogen production, which is 5-orders of magnitude higher than that of pristine PFBT polymer under the same catalytic conditions. Detailed kinetics studies suggest that the productive electron transfer quench of the excited state of Pdots by an electron donor is about 40%. More importantly, we also found that the Pdots can tolerate oxygen during catalysis, which is crucial for further application of this material for light-driven water splitting.
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