| 1. |
- Andreasson, Joakim, 1973, et al.
(författare)
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Efficient non-radiative deactivation and conformational flexibility of meso-diaryloctaalkylporphyrins in the excited triplet state
- 2000
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Ingår i: Journal of Physical Chemistry A. - 1089-5639 .- 1520-5215. ; 104:41, s. 9307-9314
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Tidskriftsartikel (refereegranskat)abstract
- The excited triplet state deactivation of zinc(II) meso-diaryloctaalkylporphyrins (ZnDAOAP) has been studied over a wide temperature range using transient triplet-triplet absorption spectroscopy together with steady-state and time-resolved phosphorescence techniques, The results from transient absorption measurements show that the depopulation of the initially formed triplet state (T-1A state) is unusually fast at temperatures above 150 K. The efficiency of the deactivation originates from a spin allowed transition to a second tripler state (T-1B state), The transformation process T-1A-->T-1B is therefore the dominating deactivation channel of the T-1A state in this temperature range, and direct intersystem crossing T-1A-->S-0 makes negligible contribution. The subsequent ground-state recovery T-1B-->S-0 is also very efficient in comparison to many other porphyrins. Due to the substantial activation energy found for the transformation process, it most likely involves a conformational distortion of the porphyrin macrocycle. At low temperature, however, the relaxation of the T-1A State occurs by direct intersystem crossing to the ground state.
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| 2. |
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| 3. |
- Kajanus, Johan, 1967, et al.
(författare)
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Synthesis of bis(phenylethynyl)arylene-linked diporphyrins designed for studies of intramolecular energy transfer
- 1999
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Ingår i: Synthesis. - 0039-7881 .- 1437-210X. ; :7, s. 1155-1162
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Tidskriftsartikel (refereegranskat)abstract
- A series of donor-bridge-acceptor systems has been designed to give information on how the medium between the donor and the acceptor influences the excitation energy transfer process. The donor and the acceptor are zinc and free base porphyrins, respectively. The systems were obtained by a synthetic strategy that guarantees a precise state of metalation, i.e. by a building block approach in which a third chromophore is formed as the two porphyrins are covalently linked together in a geometrically well defined structure. The porphyrins are linked by one of the three different bridge chromophores; 9,10-bis(phenylethynyl)anthracene, or 1,4-bis(phenylethynyl)-substituted benzene or naphthalene. The different units were assembled using copper-free, palladium-catalyzed cross-coupling of aryl iodides with terminal alkynes. Reference compounds that correspond to different parts of the systems have also been prepared.
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| 4. |
- Kajanus, Johan, 1967
(författare)
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Synthesis of Covalently Linked Diporphyrins: Model Compounds for Intramolecular Energy and Electron Transfer
- 2000
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Three series of donor-bridge-acceptor compounds have been synthesized to probe the influence of various bridge chromophores on energy and electron transfer. The donor-bridge-acceptor compounds in each series comprise two different porphyrins, acting as donor and acceptor, covalently linked by bridge chromophores. The bridge chromophores are 9,10-bis(phenylethynyl)anthracene and 1,4-bis(phenylethynyl) substituted benzene, naphthalene, and bicyclo[2.2.2]octane. The first series consists of zinc/free base diporphyrins, which were assembled using a building block approach. The starting materials were porphyrins and bridge building blocks functionalized with ethyne or iodide. Each bridge chromophore was formed as the building blocks were covalently linked using a palladium-catalyzed coupling reaction (Sonogashira reaction). The second series was prepared by converting the zinc/free base diporphyrins to their zinc/iron(III) analogs. The free base moiety was metallated to the iron(III) chloride porphyrin using FeCl2. Despite the paramagnetic nature of the iron(III) porphyrins, these mixed metal diporphyrins and iron porphyrin monomers could be characterized using 1H NMR. The zinc/iron(III) diporphyrins were converted to the corresponding free base/iron(III) diporphyrins by acid treatment. Finally, zinc/gold(III) diporphyrins were synthesized using a building block synthesis as well as from a bis(free base porphyrin) dimer by a sequence of gold insertion followed by zinc insertion. Steady state and time resolved spectroscopic measurements have shown that singlet energy transfer from the zinc porphyrin to the free base porphyrin in these systems is strongly dependent on the bridge chromophore. Similar results were obtained in a study of triplet energy transfer. In contrast to previous work on similar systems, we did not detect electron transfer in the diporphyrins with iron porphyrins as electron acceptors. Preliminary investigations of the zinc/gold(III) diporphyrins indicate that these systems display bridge dependent electron transfer.
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| 5. |
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| 6. |
- Kilså-Jensen, Kristine, 1972, et al.
(författare)
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Mediated energy transfer in covalently linked porphyrin dimers
- 1997
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Ingår i: Journal of Physical Chemistry A. - 1089-5639 .- 1520-5215. ; 101:12, s. 2218-2220
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Tidskriftsartikel (refereegranskat)abstract
- Donor-acceptor systems where the rate of radiationless electronic energy transfer is influenced by the electronic structure of the intervening medium are studied. In this paper we report the observation of mediated energy transfer in a series of geometrically well-defined porphyrin dimers. The dimers consist of a free base porphyrin (5,15-diphenyl-alpha,beta-octaalkylporphyrin, H2P) and the corresponding zinc porphyrin (ZnP) as acceptor and donor, respectively, connected by aryl chromophores with varying energies of the lowest excited states.
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| 7. |
- Kilså, Kristine, 1972, et al.
(författare)
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Bridge-dependent electron transfer in porphyrin-based donor-bridge-acceptor systems
- 2001
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Ingår i: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 1520-5126 .- 0002-7863. ; 123:13, s. 3069-3080
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Tidskriftsartikel (refereegranskat)abstract
- Photoinduced electron transfer in donor-bridge-acceptor systems with zinc porphyrin (or its pyridine complex) as the donor and gold(III) porphyrin as the acceptor has been studied. The porphyrin moieties were covalently linked with geometrically similar bridging chromophores which vary only in electronic structure. Three of the bridges are fully conjugated pi -systems and in a fourth, the conjugation is broken. For systems with this bridge, the quenching rate of the singlet excited state of the donor was independent of solvent and corresponded to the rate of singlet energy transfer expected for a Forster mechanism. In contrast, systems with a rr-conjugated bridging chromophore show a solvent-dependent quenching rate that suggests electron transfer in the Marcus normal region. This is supported by picosecond transient absorption measurements, which showed formation of the zinc porphyrin radical cation only in systems with pi -conjugated bridging chromophores. On the basis of the Marcus and Rehm-Weller equations, an electronic coupling of 5-20 cm(-1) between the donor and acceptor is estimated for these systems. The largest coupling is found for the systems with the smallest energy gap between the donor and bridge singlet excited states. This is in good agreement with the coupling calculated with quantum mechanical methods, as is the prediction of an almost zero coupling in the systems with a nonconjugated bridging chromophore.
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| 8. |
- 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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| 9. |
- Kilså, Kristine, 1972, et al.
(författare)
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Mediated electronic coupling: Singlet energy transfer in porphyrin dimers enhanced by the bridging chromophore
- 1999
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Ingår i: Journal of Physical Chemistry B Materials. - 1089-5647. ; 103:34, s. 7329-7339
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Tidskriftsartikel (refereegranskat)abstract
- We have studied singlet electronic energy transfer (EET) in two donor-bridge-acceptor series (D-B -A), in which the donor (zinc porphyrin or its pyridine complex) and the acceptor (free base porphyrin) were covalently connected by a geometrically well-defined bridging chromophore. We have investigated how the medium between a donor and an acceptor influences EET by separating the influence of the electronic structure of the bridging chromophore from other effects known to influence the energy transfer. The electronic structure of the bridging chromophore was varied by changing the central unit (bicyclo[2.2.2]octane, benzene, naphthalene, or anthracene) in the bridging chromophore. In all systems the excited state energy separation donor-bridge and bridge-acceptor is large enough to prevent stepwise singlet energy transfer. In addition, the systems were designed to minimize conjugation to preserve the identity of the separate chromophores (donor, bridge, acceptor). Compared with the rate constant expected from the Forster theory, the bridging chromophore with bicyclo[2.2.2]octane as the central unit did not significantly enhance the energy transfer rate constant. However, the bridging chromophores with benzene and naphthalene as the central unit showed a moderate increase, whereas the bridging chromophore with anthracene as the central unit showed the largest increase in energy transfer rate constant. This increase is ascribed to a mediating effect of the bridging chromophore and it is proposed to be strongly correlated to the energy splitting between the singlet excited states of donor and bridging chromophores.
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| 10. |
- Wittung, Pernilla, 1968, et al.
(författare)
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Phospholipid membrane permeability of peptide nucleic acid
- 1995
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Ingår i: FEBS Letters. - : Wiley. - 1873-3468 .- 0014-5793. ; 365:1, s. 27-29
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Tidskriftsartikel (refereegranskat)abstract
- Phospholipid vesicles (liposomes) as membrane models have been used to study the penetration properties of peptide nucleic acid (PNA), a new DNA analog in which the nucleobases are attached to a pseudo-peptide backbone, The liposomes were characterised by carboxyfluorescein efflux, light-scattering and cryogenic transmission electron microscopy. The liposome structure was found not to be affected by the incorporation of PNA or an oligonucleotide. Two 10-mer fluorescein-labelled PNAs were found to have low efflux rates (half-times of 5.5 and 11 days), comparable to a 10-mer oligonucleotide (half-time of 7 days). We conclude that passive diffusion of unmodified PNA is not an effective way of transport into biological cells.
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| 11. |
- Wu, Haibo, 1989-, et al.
(författare)
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Heterogeneous Copper-Catalyzed Cross-Coupling for Sustainable Synthesis of Chiral Allenes : Application to the Synthesis of Allenic Natural Products
- 2023
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Ingår i: Angewandte Chemie International Edition. - : Wiley. - 1433-7851 .- 1521-3773. ; 62:50
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Tidskriftsartikel (refereegranskat)abstract
- Classical Crabbé type SN2' substitutions of propargylic substrates has served as one of the standard methods for the synthesis of allenes. However, the stereospecific version of this transformation often requires either stoichiometric amounts of organocopper reagents or special functional groups on the substrates, and the chirality transfer efficiency is also capricious. Herein, we report a sustainable methodology for the synthesis of diverse 1,3-di and tri-substituted allenes by using a simple and cheap cellulose supported heterogeneous nanocopper catalyst (MCC-Amp-Cu(I/II)). This approach represents the first example of heterogeneous catalysis for the synthesis of chiral allenes. High yields and excellent enantiospecificity (up to 97 % yield, 99 % ee) were achieved for a wide range of di- and tri-substituted allenes bearing various functional groups. It is worth noting that the applied heterogeneous catalyst could be recycled at least 5 times without any reduced reactivity. To demonstrate the synthetic utility of the developed protocol, we have applied it to the total synthesis of several chiral allenic natural products.
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