| 11. |
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| 12. |
- Göransson, Erik
(author)
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Bridge Mediated Electron Transfer in Conjugated and Cross-Conjugated Donor-Acceptor Compounds
- 2012
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Doctoral thesis (other academic/artistic)abstract
- Detailed understanding of electron transfer reactions is important in many aspects of chemistry, biology and solar energy conversion.The main aim of this thesis is to provide further insight into electron transfer through highly conjugated bridge structures. Towards this end, three series of donor-acceptor dyads have been studied, all using an oligo(1,4-phenylene-ethynylene) moiety as the bridge. A common theme in these series is that they explore the effects of having either an ethynylene or phenylene as the attachment group between the bridge and the donor or acceptor. Photophysical characterization of these dyads was carried out by means of time resolved laser spectroscopy. The results show that having an ethynylene as attachment group results in higher rates for bridge mediated electron and energy transfer compared to similar systems, where a phenylene was used.It was also found that most of the investigated systems show a fast back electron transfer. A notable exception is a zinc(II) phthalocyanine- gold(III) porphyrin dyad, where very fast photoinduced electron transfer (kPET = 1.0×1012 s-1) was followed by relatively slow back electron transfer (kBET = 1.0×109 s-1). A complementary DFT investigation indicated that the charge shifted state involves a reduction of the gold ion, rather than the porphyrin ring. This results in lower electronic coupling between the reduced gold porphyrin and the bridge and thus slower back electron transfer.A series of zinc porphyrin platinum acetylide dyads was used to explore the effects on electronic coupling of different attachments points on the porphyrin ring. For the investigated system it was found that linking at the meso-position results in an eight-fold increase in electron transfer rate compared to the β-position.In addition, a series of mixed valence compounds was used to investigate electronic coupling mediated by cross-hyperconjugated or cross-π-conjugated bridges. The results indicate coupling elements of 100-400 cm-1, with the cross-π-conjugated bridge having the largest coupling. A complementary TD-DFT study indicates that both through bond and through space coupling can be active in these systems. The relative contribution of these two mechanisms to the electronic coupling is highly conformer dependent.
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| 13. |
- Göransson, Erik, et al.
(author)
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Charge transfer through cross-hyperconjugated versus cross-pi-conjugated bridges : an intervalence charge transfer study
- 2013
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In: Chemical Science. - : Royal Society of Chemistry (RSC). - 2041-6520 .- 2041-6539. ; 4:9, s. 3522-3532
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Journal article (peer-reviewed)abstract
- Recently there has been much interest in electron transfer and transport through cross-conjugated molecules as interesting test cases for the interplay between molecular and electronic structure as well as potential motifs in the design of new compounds for molecular electronics. Herein we expand on this concept and present the synthesis and characterization of a series of four organic mixed-valence dyads to probe the effect of the bridge structure on the electronic coupling. The electronic coupling between two triarylamine units could be mediated either by cross-hyperconjugation through a saturated ER2 bridge (E = C or Si, R = alkyl or silyl group), or via a cross-conjugated pi-system. The aim of the study is to compare the electron transfer through the various saturated bridges to that of a cross-pi-conjugated bridge. The electronic coupling in these mixed-valence compounds was determined by analysis of intervalence charge transfer bands, and was found to be in the range of 100-400 cm(-1). A complementary DFT and TD-DFT study indicated that the electronic coupling in the dyads with saturated ER2 segments is highly conformer dependant. Furthermore, the calculations showed that two types of interactions contribute to the electronic coupling; a through-bond cross-(hyper)conjugation mechanism and a through-space mechanism. Taken together, these findings suggest the possibility for new architectures for molecular electronics applications utilizing cross-hyperconjugation through properly selected saturated segments which have comparable electron transfer characteristics as regular cross-pi-conjugated molecules.
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| 14. |
- Göransson, Erik, et al.
(author)
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Long-Range Electron transfer in Zinc-Phthalocyanine-oligo(phenylene-ethynylene)-based donor-bridge-acceptor dyads
- 2012
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In: Inorganic Chemistry. - : American Chemical Society (ACS). - 0020-1669 .- 1520-510X. ; 51:21, s. 11500-11512
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Journal article (peer-reviewed)abstract
- In the context of long-range electron transfer for solar energy conversion, we present the synthesis, photophysical, and computational characterization of two new zinc(II) phthalocyanine oligophenylene-ethynylene based donor-bride-acceptor dyads: ZnPc-OPE-AuP+ and ZnPc-OPE-C60. A gold(III) porphyrin and a fullerene has been used as electron accepting moieties, and the results have been compared to a previously reported dyad with a tin(IV) dichloride porphyrin as the electron acceptor (Fortage et al. Chem. Commun.2007, 4629). The results for ZnPc-OPE-AuP+ indicate a remarkably strong electronic coupling over a distance of more than 3 nm. The electronic coupling is manifested in both the absorption spectrum and an ultrafast rate for photoinduced electron transfer (kPET = 1.0 × 1012 s–1). The charge-shifted state in ZnPc-OPE-AuP+ recombines with a relatively low rate (kBET = 1.0 × 109 s–1). In contrast, the rate for charge transfer in the other dyad, ZnPc-OPE-C60, is relatively slow (kPET = 1.1 × 109 s–1), while the recombination is very fast (kBET ≈ 5 × 1010 s–1). TD-DFT calculations support the hypothesis that the long-lived charge-shifted state of ZnPc-OPE-AuP+ is due to relaxation of the reduced gold porphyrin from a porphyrin ring based reduction to a gold centered reduction. This is in contrast to the faster recombination in the tin(IV) porphyrin based system (kBET = 1.2 × 1010 s–1), where the excess electron is instead delocalized over the porphyrin ring.
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| 15. |
- Göransson, Erik, et al.
(author)
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Photoinduced Electron Transfer in Zn(II)porphyrin-Bridge-Pt(II)acetylide Complexes : Variation in Rate with Anchoring Group and Position of the Bridge
- 2010
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In: Inorganic Chemistry. - : American Chemical Society (ACS). - 0020-1669 .- 1520-510X. ; 49:21, s. 9823-9832
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Journal article (peer-reviewed)abstract
- The synthesis and photophysical characterization of two sets of zinc porphyrin platinum acetylide complexes are reported. The two sets of molecules differ in the way the bridging phenyl-ethynyl unit is attached to the porphyrin ring. One set is attached via an ethynyl unit on the beta position, while the other set is attached via a phenyl unit on the meso position of the porphyrin. These were compared with previously studied complexes where attachment was made via an ethynyl unit on the meso position. Femtosecond transient absorption measurements showed in all systems a rapid quenching of the porphyrin singlet state. Electron transfer is suggested as the quenching mechanism, followed by an even faster recombination to form both the porphyrin ground and triplet excited states. This is supported by the variation in quenching rate and porphyrin triplet yield with solvent polarity, and the observation of an intermediate state in the meso-phenyl linked systems. The different linking motifs between the dyads resulted in significant variations in electron transfer rates.
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| 16. |
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| 17. |
- Hammarström, Leif, et al.
(author)
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Expanded bite angles in tridentate ligands : improving the photophysical properties in bistridentate Ru-II polypyridine complexes
- 2010
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In: Coordination chemistry reviews. - : Elsevier BV. - 0010-8545 .- 1873-3840. ; 254:21-22, s. 2546-2559
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Journal article (peer-reviewed)abstract
- Bistridentate metal complexes as photosensitizers are ideal building blocks in the construction of rodlike isomer-free assemblies for intramolecular photoinduced charge separation. Approaches to obtain long-lived luminescent metal-to-ligand charge transfer excited states in bistridentate Run polypyridine complexes via the manipulation of metal-centered state energies are discussed. Following an introduction to general strategies to prolong the excited state lifetimes, more recent work is explored in detail where tridentate ligands with expanded 2,2':6',2 ''-terpyridine cores are utilized. The synthesis of these tridentate ligands and their corresponding Ru-II complexes is covered. Bistridentate Run complexes with microsecond metal-to-ligand charge transfer excited state lifetimes are described, and are used in electron donor-photosensitizer-electron acceptor assemblies for efficient vectorial photoinduced charge separation.
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| 18. |
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| 19. |
- Hammarström, Leif
(author)
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Overview : Capturing the Sun for Energy Production
- 2012
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In: Ambio. - : Springer Science and Business Media LLC. - 0044-7447 .- 1654-7209. ; 41:Suppl 2, s. 103-107
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Journal article (peer-reviewed)abstract
- Solar energy has potential to provide a major part of our energy for our future, as heat, electricity, and fuels. Most solar technologies are still at the research and development stage, however. There is therefore a need for bold and enduring efforts in research, development and commercialization, including strategic legislative measures and infrastructure investments. This overview article serves as an introduction to the present Special Report, briefly outlining the potential, principles and possibilities as well as some of the challenges of solar energy conversion.
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| 20. |
- Hammarström, Leif, et al.
(author)
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Preface : Special Report: Capturing the Sun
- 2012
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In: Ambio. - : Springer Science and Business Media LLC. - 0044-7447 .- 1654-7209. ; 41:Suppl 2, s. 101-102
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Journal article (other academic/artistic)
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