| 1. |
- Pfeffer, M. G., et al.
(author)
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Palladium versus Platinum: The Metal in the Catalytic Center of a Molecular Photocatalyst Determines the Mechanism of the Hydrogen Production with Visible Light
- 2015
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In: Angewandte Chemie-International Edition. - : Wiley. - 1433-7851 .- 1521-3773. ; 54:17, s. 5044-5048
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Journal article (peer-reviewed)abstract
- To develop highly efficient molecular photocatalysts for visible light-driven hydrogen production, a thorough understanding of the photophysical and chemical processes in the photocatalyst is of vital importance. In this context, in situ X-ray absorption spectroscopic (XAS) investigations show that the nature of the catalytically active metal center in a (N boolean AND N)MCl2 (M=Pd or Pt) coordination sphere has a significant impact on the mechanism of the hydrogen formation. Pd as the catalytic center showed a substantially altered chemical environment and a formation of metal colloids during catalysis, whereas no changes of the coordination sphere were observed for Pt as catalytic center. The high stability of the Pt center was confirmed by chloride addition and mercury poisoning experiments. Thus, for Pt a fundamentally different catalytic mechanism without the involvement of colloids is confirmed.
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| 2. |
- Christensson, Niklas, et al.
(author)
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Electronic photon echo spectroscopy and vibrations
- 2010
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In: Vibrational Spectroscopy. - : Elsevier BV. - 0924-2031. ; 53:1, s. 2-5
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Conference paper (peer-reviewed)abstract
- Coupling between electronic and nuclear degrees of freedom in Rhodamine 800 has been studied using fluorescence line narrowing (FLN) and three-pulse photon echo peak shift (3PEPS). From the FLN measurement we extract the Huang-Rhys S-factors and frequencies of 16 Franck-Condon active vibrations clustered in two groups centred around 350 cm(-1) and 1400 cm(-1). The five modes below 500 cm(-1) covered by the excitation pulse spectral band create a complex beating pattern in the 3PEPS measurements. After determining the reorganisation energy of the modes involved in the peak shift measurement we are able to obtain the S-factors of the modes. The S-factors from two different experiments are in good agreement. The dephasing rates of these vibrations deviate significantly from the band-gap law. We propose that the main channel for the dephasing of the modes above 225 cm(-1) is a second order process involving one phonon and a molecular vibration. (C) 2010 Elsevier B.V. All rights reserved.
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| 3. |
- Kübel, Joachim, 1988, et al.
(author)
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Excitation Power Modulates Energy-Transfer Dynamics in a Supramolecular Ru-II-Fe-II-Ru-II Triad
- 2017
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In: Chemphyschem. - : Wiley. - 1439-4235. ; 18:20, s. 2899-2907
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Journal article (peer-reviewed)abstract
- Multichromophoric arrays are key to light harvesting in natural and artificial photosynthesis. A trinuclear, symmetric Ru-II-Fe-II-Ru-II triad may resemble a light-harvesting model system in which excitation energy from donor units (Ru-terpyridine fragments) is efficiently transferred to the acceptor (the Fe-terpyridine fragment). The photoinduced dynamics after simultaneous excitation of more than a single chromophoric unit (donor/acceptor) at varying excitation fluence is investigated in this contribution. Data suggests that energy transfer is decelerated if the acceptor states (on the Fe-II unit) are not depopulated fast enough. As a consequence, the lifetime of a high-lying excited state (centered on either of the Ru-II units) is prolonged. A kinetic model is suggested to account for this effect. Although the proposed model is specifically adopted to account for the experimental data reported here, it might be generalized to other situations in which multiple energy or electron donors are covalently linked to a single acceptor site, a situation of interest in contemporary artificial photosynthesis.
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| 4. |
- Potts, Nathan T. Z., et al.
(author)
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Probing the dye-semiconductor interface in dye-sensitized NiO solar cells
- 2020
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In: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 153:18
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Journal article (peer-reviewed)abstract
- The development of p-type dye-sensitized solar cells (p-DSSCs) offers an opportunity to assemble tandem photoelectrochemical solar cells with higher efficiencies than TiO2-based photoanodes, pioneered by O'Regan and Gratzel [Nature 353, 737-740 (1991)]. This paper describes an investigation into the behavior at the interfaces in p-DSSCs, using a series of BODIPY dyes, BOD1-3. The three dyes have different structural and electronic properties, which lead to different performances in p-DSSCs. We have applied photoelectron spectroscopy and transient absorption spectroscopy to rationalize these differences. The results show that the electronic orbitals of the dyes are appropriately aligned with the valence band of the NiO semiconductor to promote light-induced charge transfer, but charge-recombination is too fast for efficient dye regeneration by the electrolyte. We attribute this fast recombination, which limits the efficiency of the solar cells, to the electronic structure of the dye and the presence of Ni3+ recombination sites at the NiO surface.
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