Molecular Architecture and Environmental Effects in Intramolecular Electron Transfer. An Electron Paramagnetic Resonance Study

Hasharoni, Kobi; Levanon, Haim; Gaetschmann, Joerg; Schubert, Heike; Kurreck, H.; Moebius, K.

doi:10.1021/j100019a037

Cited by 27 publications

(31 citation statements)

References 5 publications

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“…[52][53][54][55] Inspection of the molecular structure of the parachute system ( Figure 8) suggests that the Z-axis of 3 *ZnP-C 60 is almost parallel to the z′ dipolar axis of 3 (ZnP •+ -C 60 •-). Thus, it is reasonable to assume that the triplet RP sublevel associated with the z′-axis is mainly populated via 3 *ZnP-C 60 .…”

Section: Resultsmentioning

confidence: 99%

Spin Dynamics of a “Parachute” Shaped Fullerene−Porphyrin Dyad

et al. 2004

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The electron spin dynamics associated with the photoinduced intramolecular electron transfer (ET) in a covalently linked malonate-strapped zinc porphyrin-fullerene (ZnP-C 60 ) dyad with "parachute" geometry was studied by time-resolved electron paramagnetic resonance (TREPR) spectroscopy. Studies were carried out in widely different media, including solvents of different polarities, such as isotropic toluene and tetrahydrofuran, and anisotropic nematic liquid crystals, LCs (E-7 and ZLI-4389). Photoexcitation of the donor, ZnP, results in ET to the acceptor, C 60 , in all solvents used over a wide range of temperatures. The generated radical pairs (RPs) either decay to the ground state or produce the triplet state of the acceptor moiety, ZnP-3 *C 60 . Temperature-dependent studies permit the determination of the RP energy levels relative to the donor and acceptor singlet and triplet states. Thus, the results enable determination of the genesis of the ET routes as a function of the solvent polarity. Due to their unique dielectric properties, the LCs behave as solvents of low polarity at low temperatures and as solvents of high polarity at elevated temperatures. Finally, the triplet EPR line shape of ZnP-3 *C 60 oriented in the LCs verifies the asymmetric three-dimensional structure calculated recently, while the ZnP moiety in the dyad dictates the orientation of the bulky C 60 part in the LC matrixes.

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Section: Resultsmentioning

confidence: 99%

Spin Dynamics of a “Parachute” Shaped Fullerene−Porphyrin Dyad

et al. 2004

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“…We will show that the information provided by the triplet spectra can be used to independently estimate the orientational distribution function which would otherwise bring additional unknown parameters into the simulations of the spectra of TAPD+'NQ -'. In contrast to previous studies of molecular and radical pair triplet states of porphyrins in liquid crystals [9][10][11][12][13][14][15][16], we will base the orientational distribution on a model of the interactions between the solute and solvent and will take the porphyfin side groups explicitly into account. The geometric parameters for the calculation of the radical pair spectra will be taken from the structure of the complex obtained by combining the X-ray structures of the components.…”

Section: Introductionmentioning

confidence: 99%

Separation of the exchange and dipolar contributions to the spin-spin coupling in the donor-acceptor complex TAPD-ZnP-NQ

et al. 1997

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Abstraet. The donor-acceptor complex, 2-tetraalkylphenylenediamine-zinc porphyrin-2-naphthoquinone (TAPD-ZnP-NQ), is studied using transient EPR at K-band (24 GHz). Spin polarized spectra of the radical pair TAPD+'NQ -" and of the triplet state TAPD-3ZnP-NQ are observed simultaneously following light exeitation of the complex at 30 K in ~ozen solutions 2-methyl-tetrahydrofuran and the liquid crystal BDH E7. In the liquid crystal, the complex is partially ordered and the spectra depend on the orientation of the sample with respect to the magnetic field. The orientational distribution function is obtained independently by simulating the spectra of the triplet state and assuming that the principal axes of the order matrix coincide with those of the inertia tensor as has been found for solutes in nematie phases. The spectra of TAPD+'NQ -" are analyzed on the basis of the coupled correlated radical pair (CCRP) model using ah estimate of the geometry based on the X-ray crystal structures of the components and the independently obtained orientational distribution function. It is shown that the experimental speetra are eonsistent with the assumed geometry and that the exchange coupling, J, is approximately 0.1 mT. This value is at least two orders of magnitude larger than that found in the analogous radical pair P+'Q-" in photosynthetic reaction centres. This difference is rationalized in terms of different mechanisms for the exchange coupling.

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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: 55%

“…The magnitude of the splitting is twice as large as the splitting at 0° rotation. The line splitting of the spectra and the angular dependence are in obvious contrast to the behavior of the P-Qs with benzoquinone acceptors [9][10][11]. A reasonable interpretation for the rotational dependence of the EPR spectra is a preferred orientation of the P-Qs in the nematic and soft glass phase in a way that both the porphyrin z-axis and the z'-axis of the biradical are perpendicular to the director.…”

Section: Time-resolved Epr Of the P-q A -Qe Triads In Liquid Crystalsmentioning

confidence: 90%

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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Molecular Architecture and Environmental Effects in Intramolecular Electron Transfer. An Electron Paramagnetic Resonance Study

Cited by 27 publications

References 5 publications

Spin Dynamics of a “Parachute” Shaped Fullerene−Porphyrin Dyad

Spin Dynamics of a “Parachute” Shaped Fullerene−Porphyrin Dyad

Separation of the exchange and dipolar contributions to the spin-spin coupling in the donor-acceptor complex TAPD-ZnP-NQ

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

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