Photoinduced Intraensemble Electron Transfer in a Base-Paired Porphyrin-Quinone System. Time-Resolved EPR Spectroscopy

Berman, Assia; Izraeli, Elad S.; Levanon, Haim; Wang, Bing; Sessler, Jonathan L.

doi:10.1021/ja00136a024

Cited by 90 publications

(59 citation statements)

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“…In subsequent papers similar experiments on P-Qs were reported using liquid crystals as solvent [9][10][11][12]. The observed changes of the polarization pattern of the RP were attributed, inter alia, to simultaneous triplet and singlet ET routes in the nematic and soft glass phase of these media.…”

Section: Introductionmentioning

confidence: 56%

EPR studies of photoinduced electron transfer in triad model compounds of photosynthesis

et al. 1998

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Time-resolved EPR spectra are reported for porphyrin-quinone-quinone and porphyrin-porphyrin-quinone triads obtained after photoexcitation in the nematic and soft glass phase of liquid crystals. Spin-polarized EPR spectra were observed for the triplet states of the porphyrin created by spin-selective intersystem crossing (ISC) from the excited singlet state and those of the charge-separated radical pair states (RP) generated by electron transfer (ET) processes. The EPR polarization patterns of the RP are discussed in terms of the favored decay channel of the photoexcited singlet state of the porphyrin donor. The decay pathway may either be singlet ET to the quinone(s) followed by singlet/triplet mixing to yield RPs with triplet character or triplet ET after ISC from the porphyrin singlet to the triplet state, or a superposition of both pathways. It is demonstrated that the nature of the linking bridge between donor and acceptor, i.e., aliphatic cyclohexylene or aromatic phenylene, significantly influences the ET mechanism and thus the polarization patterns of the RP spectra. Using liquid crystals, information about the orientation of the guest molecules in the liquid crystal matrix with respect to the long axes of the liquid crystal molecules can be obtained. In the porphyrin-porphyrin-quinone triads the energy and ET processes strongly depend on the type of metallation of the porphyrins, specifically, whether the distal, the vicinal or both porphyrins bear a zinc atom.

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Section: Introductionmentioning

confidence: 56%

EPR studies of photoinduced electron transfer in triad model compounds of photosynthesis

et al. 1998

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“…These findings are rationalized in terms of intraensemble ET (Fig. 1) occurring from the lowest excited triplet state of the donor (zinc(II) porphyrin) to the acceptor (dinitrobenzene) and by spin polarization effects [21,22]. The narrow EPR signal is attributed to a long-distance charge-separated spin-correlated radical pair (SCRP).…”

Section: Mechanistic Approach Of Model Photosynthesismentioning

confidence: 86%

Triplet porphyrins as donors in intramolecular electron transfer and their intermolecular interaction with free radicals

Blank

Galili

Levanon

2001

J. Porphyrins Phthalocyanines

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Porphyrins and related compounds are basic moieties which upon photoexcitation produce paramagnetic transients important to many processes in biology, material science and light–energy conversion. This short review demonstrates the application of time-resolved EPR spectroscopy to two processes in which the photoexcited singlet and/or triplet are involved: (1) intramolecular electron transfer in photoexcited donor–acceptor systems embedded in liquid crystals, where the porphyrins are the electron donors attached to different types of acceptors; and (2) intermolecular magnetic interactions between photoexcited porphyrin triplets and free radicals. In both systems the electron spin plays an important part with regards to the route of the magnetic interactions involved.

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“…This is a noteworthy result, considering that the driving force for ET in 7 (DG s~-43 kJ mol -1 ) is substantially less than that for 6 (DG s~-96 kJ mol -1 ). The complexities of photoinducing a PCET reaction become apparent when W-band time-resolved EPR experiments are performed on 8 [105,106]. EPR signals are observed that are consistent with intersystem crossing from the singlet to the triplet excited state prior to ET.…”

Section: Pcet Across Symmetric Hydrogen Bonding Interfacesmentioning

confidence: 91%

“…As discussed previously, this approach can be problematic because the dynamics of fluorescence decay are not necessarily specific to charge transport. Furthermore, PCET can proceed from non-emitting states to which time resolved emission spectroscopy is blind [105,141]. Accordingly, there is great benefit offered by systems that allow the PCET kinetics to be determined directly from observed charge transport intermediates.…”

Section: Pcet Model System [A]mentioning

confidence: 99%

The Relation between Hydrogen Atom Transfer and Proton‐coupled Electron Transfer in Model Systems

Hodgkiss

Rosenthal

Nocera

2006

Hydrogen‐Transfer Reactions

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Photoinduced Intraensemble Electron Transfer in a Base-Paired Porphyrin-Quinone System. Time-Resolved EPR Spectroscopy

Cited by 90 publications

References 0 publications

EPR studies of photoinduced electron transfer in triad model compounds of photosynthesis

EPR studies of photoinduced electron transfer in triad model compounds of photosynthesis

Triplet porphyrins as donors in intramolecular electron transfer and their intermolecular interaction with free radicals

The Relation between Hydrogen Atom Transfer and Proton‐coupled Electron Transfer in Model Systems

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