| 1. |
- Terazono, Y., et al.
(författare)
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Photonic control of photoinduced electron transfer via switching of redox potentials in a photochromic moiety
- 2004
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Ingår i: Journal of Physical Chemistry B. ; 108:6, s. 1812-1814
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Tidskriftsartikel (refereegranskat)abstract
- A porphyrin (P) has been covalently linked to a photochromic dihydroindolizine moiety (DHI) to form a P-DHI dyad. When the dihydroindolizine is in its closed, spirocyclic form (DHIc), the photophysics of the attached porphyrin are unaffected. Irradiation with UV light opens the photochromic moiety to the betaine form (DHIo), which has a significantly higher reduction potential than DHIc. Light absorption by the porphyrin moiety of P-DHIo is followed by rapid (50 ps) photoinduced electron transfer to yield the P.+-DHIo(.-) charge-seperated state. This state recombines in 2.9 ps to give the ground state. Irradiation of P-DHIo with light at wavelengths > 590 nm induces photoisomerization back to P-DHIc. Thermal closing can also be achieved. Thus, light is used to switch photoinduced electron transfer on or off. These principles may be useful in the design of molecular optoelectronic devices.
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| 2. |
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| 3. |
- Andreasson, Joakim, 1973, et al.
(författare)
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The gold porphyrin first excited singlet state
- 2002
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Ingår i: Photochemistry and Photobiology. - 0031-8655 .- 1751-1097. ; 76:1, s. 47-50
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Tidskriftsartikel (refereegranskat)abstract
- Gold porphyrins are often used as electron-accepting chromophores in artificial photosynthetic constructs. Because of the heavy atom effect, the gold porphyrin first-excited singlet state undergoes rapid intersystem crossing to form the triplet state. The lowest triplet state can undergo a reduction by electron donation from a nearby porphyrin or another moiety. In addition, it can be involved in triplet-triplet energy transfer interactions with other chromophores. In contrast, little has been known about the short-lived singlet excited state. In this work, ultrafast time-resolved absorption spectroscopy has been used to investigate the singlet excited state of Au(III) 5,15-bis(3,5-di-t-butylphenyl)-2,8,12,18,-tetraethyl-3,7,13,17-tetrameth ylporphyrin in ethanol solution. The excited singlet state is found to form with the laser pulse and decay with a time constant of 240 fs to give the triplet state. The triplet returns to the ground state with a lifetime of 400 ps. The lifetime of the singlet state is comparable with the time constants for energy and photoinduced electron transfer in some model and natural photosynthetic systems. Thus, it is kinetically competent to take part in such processes in suitably designed supermolecular systems.
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| 4. |
- Kodis, G., et al.
(författare)
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Energy and photoinduced electron transfer in a wheel-shaped artificial photosynthetic antenna-reaction center complex
- 2006
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Ingår i: Journal of the American Chemical Society. ; 128:6, s. 1818-1827
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Tidskriftsartikel (refereegranskat)abstract
- Functional mimics of a photosynthetic antenna-reaction center complex comprising five bis(phenylethynyl)anthracene antenna moieties and a porphyrin-fullerene dyad organized by a central hexaphenylbenzene core have been prepared and studied spectroscopically. The molecules successfully integrate singlet-singlet energy transfer and photoinduced electron transfer. Energy transfer from the five antennas to the porphyrin occurs on the picosecond time scale with a quantum yield of 1.0. Comparisons with model compounds and theory suggest that the Foster mechanism plays a major role in the extremely rapid energy transfer, which occurs at rates comparable to those seen in some photosynthetic antenna systems. A through-bond, electron exchange mechanism also contributes. The porphyrin first excited singlet state donates an electron to the attached fullerene to yield a P.+-C-60(.-) charge-separated state, which has a lifetime of several nanoseconds. The quantum yield of charge separation based on light absorbed by the antenna chromophores is 80% for the free base molecule and 96% for the zinc analogue.
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| 5. |
- Liddell, P. A., et al.
(författare)
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Photoinduced electron transfer in a symmetrical diporphyrin-fullerene triad
- 2004
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Ingår i: Physical Chemistry Chemical Physics. ; 6:24, s. 5509-5515
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Tidskriftsartikel (refereegranskat)abstract
- Two triad molecules consisting of either two zinc, or two free-base porphyrins symmetrically joined to a fullerene via phenyleneethynylene-containing linkages have been synthesized, and their photochemistry investigated. In the zinc form of the triad, P-Zn-C-60-P-Zn, excitation of a zinc porphyrin in 2-methyltetrahydrofuran solution is followed by photoinduced electron transfer to the fullerene with a time constant of 20 ps. The resulting P-Zn(.+)-C-60(.-)-P-Zn charge-separated state is formed with a quantum yield of 98% and has a lifetime of 820 ps. The first excited singlet state of the free-base analog gives the P-2H(.+)-C-60(.-)-P-2H charge-separated state with a time constant of 200 ps and a yield of 98%. The charge-separated state decays with a lifetime of 2.8 ns. The difference in the rates of photoinduced electron transfer is consistent with reaction in the normal region of the Marcus-Hush relationship of transfer rate and driving force, and charge recombination is consistent with Marcus-Hush inverted behavior. The presence of the two porphyrin electron donors in these triads enhances the absorption cross section for light collection, and the molecular framework employed could be used to prepare molecules with enhanced energy conversion or optoelectronic properties.
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| 6. |
- Liddell, P. A., et al.
(författare)
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Photonic switching of photoinduced electron transfer in a dihydropyrene-porphyrin-fullerene molecular triad
- 2004
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Ingår i: Journal of the American Chemical Society. ; 126:15, s. 4803-4811
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Tidskriftsartikel (refereegranskat)abstract
- Photonic control of photoinduced electron transfer has been demonstrated in a dimethyldihydropyrene (DHP) porphyrin (P) fullerene (C-60) molecular triad. In the DHP-P-C-60 form of the triad, excitation of the porphyrin moiety is followed by photoinduced electron transfer to give a DHP-P.+-C-60(.-) charge-separated state, which evolves by a charge shift reaction to DHP.+-P-C-60(.-). This final state has a lifetime of 2 mus and is formed in an overall yield of 94%. Visible (greater than or equal to300 nm) irradiation of the triad leads to photoisomerization of the DHP moiety to the cyclophanediene (CPD). Excitation of the porphyrin moiety of CPD-P-C-60 produces a short-lived (
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| 7. |
- Straight, S. D., et al.
(författare)
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Molecular AND and INHIBIT gates based on control of porphyrin fluorescence by photochromes
- 2005
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Ingår i: Journal of the American Chemical Society. ; 127:26, s. 9403-9409
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Tidskriftsartikel (refereegranskat)abstract
- A molecular triad consisting of a porphyrin (P) covalently linked to two photochromes - one from the dihydroindolizine family (DHI) and one from the dihydropyrene family (DHP) - has been synthesized and found to act as either a molecular AND logic gate or an INHIBIT gate, depending on the inputs and initial state of the photochromes. The basis of these functions is quenching of porphyrin fluorescence (output of the gates) by the photochromes. The spiro form of DHI does not quench porphyrin fluorescence, whereas its betaine isomer strongly quenches by photoinduced electron transfer. DHP also quenches porphyrin fluorescence, but its cyclophanediene isomer does not. The triad has been designed using suitable energetics and electronic interactions, so that although these quenching phenomena may be observed, independent isomerization of the attached photochromes still occurs. This makes it possible to switch porphyrin fluorescence on or off by isomerization of the photochromes using various combinations of inputs such as UV light, red light, and heat.
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| 8. |
- Straight, S. D., et al.
(författare)
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Photochromic control of photoinduced electron transfer. Molecular double-throw switch
- 2005
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Ingår i: Journal of the American Chemical Society. ; 127:8, s. 2717-2724
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Tidskriftsartikel (refereegranskat)abstract
- A molecular double-throw switch that employs a photochromic moiety to direct photoinduced electron transfer from an excited state donor down either of two pathways has been prepared. The molecular triad consists of a free base porphyrin (P) linked to both a C-60 electron acceptor and a dihydroindolizine (DHI) photochrome. Excitation of the porphyrin moiety of DHI-P-C-60 results in photoinduced electron transfer with a time constant of 2.3 ns to give the DHI-P.+-C-60(.-) charge-separated state with a quantum yield of 82%. UV (366 nm) light photoisomerizes the DHI moiety to the betaine (BT) form, which has a higher reduction potential than DHI. Excitation of the porphyrin of BT-P-C-60 is followed by photoinduced electron transfer with a time constant of 56 ps to produce BT.--P.+-C-60 in 99% yield. Isomerization of BT-P-C-60 back to DHI-P-C-60 may be achieved with visible light, or thermally. Thus, photoinduced charge separation originating from the porphyrin is reversibly directed down either of two different pathways by photoisomerization of the dihydroindolizine. The switch may be cycled many times.
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