| 1. |
- Kilså, Kristine, et al.
(författare)
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Enhanced Intersystem Crossing in Donor/Acceptor Systems Based on Zinc/Iron or Free-Base/Iron Porphyrins
- 2001
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Ingår i: Chemistry, A European Journal. - 1521-3765 .- 0947-6539. ; 7:10, s. 2122-33
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Tidskriftsartikel (refereegranskat)abstract
- The deactivation pathways of the singlet excited state of a series of zinc or free-base donor porphyrins covalently linked by a bridge to a paramagnetic iron(iii) chloride porphyrin acceptor have been studied. These donor-bridge-acceptor systems all share a similar geometry (25 Å donor-acceptor center-to-center distance), but the bridges vary in electronic structure. In previously reported investigations of zinc/iron porphyrin systems, the fluorescence quenching of the donor has predominantly been assigned to electron transfer. However, for the porphyrin systems studied in this paper, we show that the dominant deactivation channels are enhanced intersystem crossing and singlet energy transfer. In both series, the intersystem crossing rate (S1T1) of the donor moiety is almost doubled in the presence of a paramagnetic high-spin metal-porphyrin acceptor. The significant spectral overlap of the donor fluorescence and acceptor absorption in both series allows for efficient singlet energy transfer (Förster mechanism). Furthermore, the bridging chromophores mediate energy transfer and the enhancement is inversely dependent upon the energy gap between the donor and bridge excited states. Although Marcus theory predicts thermodynamically favorable electron transfer to occur in the systems investigated, the quenching rate constants were found to be independent of solvent polarity, and no charge-separated state could be detected, indicating very small electronic coupling for electron transfer.Supporting information for this article is available on the WWW under http://www.wiley-vch.de/contents/jc_2111/2001/f2779_s.pdf or from the author. 1H NMR spectra of FeP, FeP-OB, FeP-BB, FeP-NB, FeP-AB, ZnP-OB-FeP, ZnP-BB-FeP, ZnP-NB-FeP, and ZnP-AB-FeP.
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| 2. |
- Macpherson, Alisdair N, et al.
(författare)
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Efficient Energy Transfer from the Carotenoid S2 State in a Photosynthetic Light-Harvesting Complex
- 2001
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Ingår i: Biophysical Journal. ; 80:2, s. 923-30
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Tidskriftsartikel (refereegranskat)abstract
- Previously, the spatial arrangement of the carotenoid and bacteriochlorophyll molecules in the peripheral light-harvesting (LH2) complex from Rhodopseudomonas acidophila strain 10050 has been determined at high resolution. Here, we have time resolved the energy transfer steps that occur between the carotenoid's initial excited state and the lowest energy group of bacteriochlorophyll molecules in LH2. These kinetic data, together with the existing structural information, lay the foundation for understanding the detailed mechanisms of energy transfer involved in this fundamental, early reaction in photosynthesis. Remarkably, energy transfer from the rhodopin glucoside S2 state, which has an intrinsic lifetime of ~120 fs, is by far the dominant pathway, with only a minor contribution from the longer-lived S1 state.
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| 3. |
- Zietz, Burkhard, et al.
(författare)
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Resolution of ultrafast excited state kinetics of bilirubin in chloroform and bound to human serum albumin
- 2004
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Ingår i: Physical Chemistry, Chemical Physics - PCCP. - : Royal Society of Chemistry (RSC). - 1463-9076 .- 1463-9084. ; 6:19, s. 4535-4537
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Tidskriftsartikel (refereegranskat)abstract
- The Z–E-isomerisation of bilirubin upon excitation with visible light is a fundamental step in phototherapy of newborns with neonatal jaundice. Here we report results of an ultrafast optical spectroscopy study of bilirubin in CHCl3 as well as bound to human serum albumin. The data show that the initially excited singlet state has sub-ps decay times with major amplitude. Transient absorption measurements reveal that the ultrafast decay of the emission is accompanied by the formation of a transient intermediate which decays on the 15–20 ps timescale. The initial photoprocesses are thus considerably faster than the previously reported fastest lifetimes for bilirubin and this is, to our knowledge, the first time that the earliest processes in excited bilirubin have been resolved.
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