| 1. |
- Marcellini, Moreno, et al.
(author)
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Transient isomers in the photodissociation of bromoiodomethane
- 2018
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In: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 148:13
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Journal article (peer-reviewed)abstract
- The photochemistry of halomethanes is fascinating for the complex cascade reactions toward either the parent or newly synthesized molecules. Here, we address the structural rearrangement of photodissociated CH2IBr in methanol and cyclohexane, probed by time-resolved X-ray scattering in liquid solution. Upon selective laser cleavage of the C-I bond, we follow the reaction cascade of the two geminate geometrical isomers, CH2I-Br and CH2Br-I. Both meta-stable isomers decay on different time scales, mediated by solvent interaction, toward the original parent molecule. We observe the internal rearrangement of CH2Br-I to CH2I-Br in cyclohexane by extending the time window up to 3 mu s. We track the photoproduct kinetics of CH2Br-I in methanol solution where only one isomer is observed. The effect of the polarity of solvent on the geminate recombination pathways is discussed. Published by AIP Publishing.
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| 2. |
- Nimmrich, Amke, 1995, et al.
(author)
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Solvent-Dependent Structural Dynamics in the Ultrafast Photodissociation Reaction of Triiodide Observed with Time-Resolved X-ray Solution Scattering
- 2023
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In: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 0002-7863 .- 1520-5126. ; 145:29, s. 15754-15765
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Journal article (peer-reviewed)abstract
- Resolving the structural dynamics of bond breaking, bond formation, and solvation is required for a deeper understanding of solutionphase chemical reactions. In this work, we investigate the photodissociation of triiodide in four solvents using femtosecond time-resolved X-ray solution scattering following 400 nm photoexcitation. Structural analysis of the scattering data resolves the solvent-dependent structural evolution during the bond cleavage, internal rearrangements, solvent-cage escape, and bond reformation in real time. The nature and structure of the reaction intermediates during the recombination are determined, elucidating the full mechanism of photodissociation and recombination on ultrafast time scales. We resolve the structure of the precursor state for recombination as a geminate pair. Further, we determine the size of the solvent cages from the refined structures of the radical pair. The observed structural dynamics present a comprehensive picture of the solvent influence on structure and dynamics of dissociation reactions.
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| 3. |
- Petersson, Jonas, 1980-, et al.
(author)
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Interligand Electron Transfer Dynamics in the MLCT Excited State of Ru(4,4’-dicarboxylate-2,2’-bipyridine)2cis(NCS)2 Studied by Transient IR Absorption Anisotropy
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Other publication (other academic/artistic)abstract
- We have studied the interligand electron transfer (ILET) in the N712 dye (deprotonated N3) by means of IR transient IR absorption anisotropy. By probing vibrational transitions in the IR we can provide stronger evidence than previous studies that probed the electronic transitions in the visible. The results show that the observation of ILET is limited by the rotational time of the complex, and this gives a lower rate of 800 ns for ILET. Previously reported results have been both very fast and very slow, with timeconstants 20 ps and 3 ns respectively and the results presented here supports the slower rate. The initial anisotropy trace show an increase with a 5 ps time-constant, and the initial value corresponds to what is expected for a delocalized state. We note however that the time-scale of delocalization is unexpectedly slow.
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| 4. |
- Petersson, Jonas, 1980-, et al.
(author)
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Time-Resolved Electron Transfer in Porphyrin-Coordinated Ruthenium Dimers: From Mixed-Valence Dynamics to Hot Electron Transfer
- 2015
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In: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 119:9, s. 4479-4487
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Journal article (peer-reviewed)abstract
- Presented here is the first effort to study the formation and dynamics of the triruthenium cluster (Ru3O) pyrazine-bridged dimer mixed-valence state. Femtosecond transient absorption spectroscopy was implemented to follow photoinduced electron-transfer reactions in a series of asymmetric porphyrin-coordinated dyads, which form strongly coupled mixed-valence species upon single reduction. Excitation of the porphyrin subunit resulted in electron transfer to the Ru3O dimer with a time constant τ ≈ 0.6 ps. The intramolecular electron transfer was confirmed by excitation of the Ru3O MLCT, which resulted in the formation of a vibrationally unrelaxed porphyrin ground state. Under both excitation experiments, the back electron transfer was extremely fast (τCR < 0.1 ps), preventing complete time-resolved exploration of the mixed-valence state. These complexes enabled the observation of excited product states following electron-transfer processes, resulting from porphyrin S1 and S2 excitation. Although the charge recombination itself could not be observed, the yield of unrelaxed ground states supports the conclusion that delocalization takes place at least partially on a sub-100 fs time scale.
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| 5. |
- Petersson, Jonas, 1980-, et al.
(author)
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Ultrafast Electron Transfer Dynamics in a Series of Porphyrin/Viologen Complexes : Involvement of Electronically Excited Radical Pair Products
- 2015
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In: Journal of Physical Chemistry B. - : American Chemical Society (ACS). - 1520-6106 .- 1520-5207. ; 119:24, s. 7531-7540
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Journal article (peer-reviewed)abstract
- Ultrafast electron transfer was studied for a series of metalloporphyrin/bipyridinium complexes in aqueous solution, using laser excitation in the Soret or Q-bands of the porphyrin. Electron transfer occurred before electronic and vibrational relaxation of the initial excited state. This allowed for a thorough investigation of the dependence of electron transfer rate constants on the driving force and the nature of the product state. The driving force dependence showed that electron transfer from the S-2 state occurred to an electronically excited radical pair state, and the present results provide the most direct evidence to date for the formation of such states in photoinduced electron transfer reactions. We also found that subsequent recombination of the radical pair produced vibrationally excited ground states; the excess energy of the radical pair generated from the initial state is not completely dissipated during the lifetime of the radical pair. The porphyrin/bipyridinium complexes where recombination lies deeper in the Marcus inverted region show less formation of unrelaxed ground states, contrary to what is expected from equilibrium electron transfer theories. Instead, the rate of the electron transfer, which competes with vibrational relaxation, was the main parameter controlling the relative yield of unrelaxed ground states within this series of complexes.
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| 6. |
- Petersson, Jonas, 1980-
(author)
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Ultrafast, Non-Equilibrium Electron Transfer Reactions of Molecular Complexes in Solution
- 2014
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Doctoral thesis (other academic/artistic)abstract
- Photoinduced electron transfer is a fundamentally interesting process; it occurs everywhere in the natural world. Studies on electron transfer shed light on questions about the interaction between molecules and how the dynamics of these can be utilized to steer the electron transfer processes to achieve a desired goal. The goal may be to get electrons to the electrode of a solar cell, or to make the electrons form an energy rich fuel such as hydrogen, and it may also be an input or output for molecular switches. The importance of electron transfer reactions will be highlighted in this thesis, however, the main motivation is to gain a better understanding of the fundamental processes that affect the rate and direction of the electron transfer.A study of photoinduced electron transfer (ET) in a series of metallophorphyrin/bipyridinium complexes in aqueous solution provided fresh insight concerning the intimate relationship between vibrational relaxation and electron transfer. The forward electron transfer from porphyrin to bipyridinium as well as the following back electron transfer to the ground state could be observed by femtosecond transient absorption spectroscopy. Both the reactant and the product states of the ET processes were vibrationally unrelaxed, in contrary to what is assumed for most expressions of the ET rates. This could be understood from the observation of unrelaxed ground states. The excess energy given by the initial excitation of the porphyrin does not relax completely during the two steps of electron transfer. This is an unusual observation, not reported in the literature prior the studies presented in this thesis. This study also gave the first clear evidence of electronically excited radical pairs formed as products of intramolecular electron transfer. Signs of electronically excited radical pairs were seen in transient spectra, and were further verified by the observation that the rates followed a Marcus normal region behavior for all excitation wavelengths, despite the relatively large excess energy of the second excited state.This thesis also concerns electron transfer in solar cell dyes and mixed valence complexes. In the ruthenium polypyridyl complex Ru(dcb)2(NCS)2, where dcb = 4,4’-dicarboxy-2,2’-bipyridine, inter-ligand electron transfer (ILET) in the 3MLCT state was followed by means of femtosecond transient absorption anisotropy that was probed in the mid-IR region. Unexpectedly, ILET was not observed because electron density was localized on the same bpy during the time-window allowed by the rotational lifetime.
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| 7. |
- Pettersson-Rimgard, Belinda, et al.
(author)
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Ultrafast Interligand Electron Transfer in cis-[Ru(4,4’-dicarboxylate-2,2’-bipyridine)2(NCS)2]4- and Implications for Electron Injection Limitations in Dye Sensitized Solar Cells
- 2018
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In: Chemical Science. - : RSC Publishing. - 2041-6520 .- 2041-6539. ; 9:41, s. 7958-7967
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Journal article (peer-reviewed)abstract
- Interligand electron transfer (ILET) of the lowest metal-to-ligand charge transfer (MLCT) state of N712 (cis-[Ru(dcb)2(NCS)2]4−, where dcb = 4,4′-dicarboxylate-2,2′-bipyridine) in a deuterated acetonitrile solution has been studied by means of femtosecond transient absorption anisotropy in the mid-IR. Time-independent B3LYP density functional calculations were performed to assign vibrational bands and determine their respective transition dipole moments. The transient absorption spectral band at 1327 cm−1, assigned to a symmetric carboxylate stretch, showed significant anisotropy. A rapid anisotropy increase (τ1 ≈ 2 ps) was tentatively assigned to vibrational and solvent relaxation, considering the excess energy available after the excited singlet–triplet conversion. Thereafter, the anisotropy decayed to zero with a time constant τ2 ≈ 240 ps, which was assigned to the rotational correlation time of the complex in deuterated acetonitrile. No other distinctive changes to the anisotropy were observed and the amplitude of the slow component at time zero agrees well with that predicted for a random mixture of MLCT localization on either of the two dcb ligands. The results therefore suggest that MLCT randomization over the two dcb ligands occurs on the sub-ps time scale. This is much faster than proposed by previous reports on the related N3 complex [Benkö et al., J. Phys. Chem. B, 2004, 108, 2862, and Waterland et al., J. Phys. Chem. A, 2001, 105, 4019], but in agreement with that found by Wallin and co-workers [J. Phys. Chem. A, 2005, 109, 4697] for the [Ru(bpy)3]2+ (bpy = 2,2′-bipyridine) complex. This suggests that electron injection from the excited dye into TiO2 in dye-sensitized solar cells is not limited by ILET.
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| 8. |
- Yamamoto, Masanori, et al.
(author)
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A Ruthenium Complex–Porphyrin–Fullerene-Linked Molecular Pentad as an Integrative Photosynthetic Model
- 2017
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In: Angewandte Chemie International Edition. - : Wiley. - 1433-7851 .- 1521-3773. ; 56:12, s. 3329-3333
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Journal article (peer-reviewed)abstract
- A ruthenium complex, porphyrin sensitizer, fullerene acceptor molecular pentad has been synthesized and a long-lived hole–electron pair was achieved in aqueous solution by photoinduced multistep electron transfer: Upon irradiation by visible light, the excited-state of a zinc porphyrin (1ZnP*) was quenched by fullerene (C60) to afford a radical ion pair, 1,3(ZnP.+-C60.−). This was followed by the subsequent electron transfer from a water oxidation catalyst unit (RuII) to ZnP.+ to give the long-lived charge-separated state, RuIII-ZnP-C60.−, with a lifetime of 14 μs. The ZnP worked as a visible-light-harvesting antenna, while the C60 acted as an excellent electron acceptor. As a consequence, visible-light-driven water oxidation by this integrated photosynthetic model compound was achieved in the presence of sacrificial oxidant and redox mediator.
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