| 1. |
- Karnahl, Michael, et al.
(författare)
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Synthesis and photophysics of a novel photocatalyst for hydrogen production based on a tetrapyridoacridine bridging ligand
- 2012
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Ingår i: Chemical Physics. - : Elsevier BV. - 0301-0104 .- 1873-4421. ; 393:1, s. 65-73
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Tidskriftsartikel (refereegranskat)abstract
- Molecular photocatalysts allow for selectively tuning their function on a molecular level based on an in-depth understanding of their chemical and photophysical properties. This contribution reports the synthesis and photophysical characterization of the novel molecular photocatalyst [(tbbpy)(2)Ru(tpac)PdCl(2)](2+) RutpacPd (with tpac = tetrapyrido[3,2-a:2',3'-c:3 '',2 ''-h:2''',3'''-j]acridine) and its mononuclear building block. Furthermore, detailed photocatalytic activity measurements of RutpacPd are presented. The introduction of the tpac-ligand into the molecular framework offers a potential route to reduce the impact of water as compared to the well-studied class of RutpphzPd (with tpphz = tetrapyrido[3,2-a:2',3'-c:300,2 ''-h: 2''',3'''-j] phenazine) complexes. The distinct impact of water on the electron-transfer processes in tpphz-ligands stems from the possibility of water to form hydrogen bonds to the phenazine nitrogen atoms and will potentially reduced when replacing the phenazine by the acridine unit. The effect of this structural variation on the catalytic properties and the underlying ultrafast intramolecular charge transfer behavior will be discussed in detail.
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| 2. |
- Karnahl, Michael, et al.
(författare)
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Tuning of Photocatalytic Hydrogen Production and Photoinduced Intramolecular Electron Transfer Rates by Regioselective Bridging Ligand Substitution
- 2011
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Ingår i: ChemPhysChem. - : Wiley. - 1439-4235 .- 1439-7641. ; 12:11, s. 2101-2109
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Tidskriftsartikel (refereegranskat)abstract
- Artificial photosynthesis based on supramolecular photocatalysts offers the unique possibility to study the molecular processes underlying catalytic conversion of photons into chemical fuels in great detail and to tune the properties of the photocatalyst by alterations of the molecular framework. Herein we focus on both possibilities in studying the photocatalytic reduction of protons by derivatives of the well-known photocatalyst [(tbbpy)(2)Ru(tpphz)PdCl(2)](PF(6))(2) [4,4'-di-tert-butyl-2,2'-bipyridine (tbbpy), tetrapyrido[3,2-a:2',3'-c:3 '',2 ''-h:2'", 3'"-j]phenazine (tpphz)]. We report on a modified photocatalyst where the crucial bridging ligand tpphz is substituted by bromine and investigate the effect of the structural variation on the catalytic properties of the complex and its ultrafast intramolecular charge transfer behavior. It is found that structural modification stabilizes the phenanthroline-centered metal-to-ligand charge-transfer state on the tpphz moiety, thereby reducing the electron transfer gradient across the entire electron-relaying bridging ligand and at the same time accelerating nanosecond ground-state recovery. The same structural modifications cause an overall reduction of the catalytic activity of the complex. Thus, the results highlight the potential of small structural variations in the molecular framework of supramolecular catalysts in understanding the photoinduced charge-transfer processes and optimizing their catalytic performance.
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| 3. |
- Kuhnt, Christian, et al.
(författare)
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The impact of bromine substitution on the photophysical properties of a homodinuclear Ru-tpphz-Ru complex
- 2011
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Ingår i: Chemical Physics Letters. - : Elsevier BV. - 0009-2614 .- 1873-4448. ; 516:1-3, s. 45-50
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Tidskriftsartikel (refereegranskat)abstract
- Ruthenium-polypyridine complexes play an important role as photosensitizers in supramolecular photocatalysis. Using multiple Ru-centers within a single supramolecular catalyst might be a promising path for improving its efficiency. The connection of several chromophores may, however, lead to direct interaction amongst individual photoactive centers, which is at the core of the work at hand. The work focuses on the photophysics of [(tbbpy)(2)Ru(3,16-Br(2)-tpphz)Ru(tbbpy)(2)](PF(6))(4) (1, tpphz = tetrapyrido[3,2-a: 2',3'-c: 3 '',2 ''-h:2''',3'''-j] phenazine, tbbpy = 4,4'-di-tert.-butyl-2,2'-bipyridine) and aims at detailing the impact of the bromine substituents on bridging ligand photoinduced intramolecular charge-transfer dynamics. It is shown that the introduction of the bromine reduces the driving force for intra-ligand charge-transfer steps and impacts exciton-exciton annihilation at high pump intensities.
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| 4. |
- Tschierlei, Stefanie, et al.
(författare)
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Photophysics of an Intramolecular Hydrogen-Evolving Ru-Pd Photocatalyst
- 2009
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Ingår i: Chemistry: A European Journal. - : Wiley. - 1521-3765 .- 0947-6539. ; 15:31, s. 7678-7688
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Tidskriftsartikel (refereegranskat)abstract
- Photoinduced electron-transfer processes within a precatalyst for intramolecular hydrogen evolution [(tbbpy)(2)Ru(tpphz)PdCl2](2+) (RuPd; tbbpy = 4,4'-di-tert-butyl-2,2'-bipyridine, tpphz = tetrapyrido[3,2-a:2',3'c:3 '',2 '',-h:2"',3'''-j]phenazine) have been studied by resonance Raman and ultrafast time-resolved absorption spectroscopy. By comparing the photophysics of the [(tbbpy)(2)Ru(tpphz)](2+) subunit Ru with that of the supramolecular catalyst RuPd, the individual electron-transfer steps are assigned to kinetic components, and their dependence on solvent is discussed. The resonance Raman data reveal that the initial excitation of the molecular ensemble is spread over the terminal tbbpy and the tpphz ligands. The subsequent excited-state relaxation of both Ru and RuPd on the picosecond timescale involves formation of the phenazine-centered intraligand charge-transfer state, which in RuPd precedes formation of the Pd-reduced state. The photoreaction in the heterodinuclear supramolecular complex is completed on a subnanosecond timescale. Taken together, the data indicate that mechanistic investigations must focus on potential rate-determining steps other than electron transfer between the photoactive center and the Pd unit. Furthermore, structural variations should be directed towards increasing the directionality of electron transfer and the stability of the charge-separated states.
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