A First High-Field EPR Study of Photoinduced Electron Transfer in a Base-Paired Porphyrin−Dinitrobenzene Supramolecular Complex

Berg, Alexis; Shuali, Zohar; Asano-Someda, Motoko; Levanon, Haim; Fuhs, Michael; Möbius, K.; Wang, Ruizheng; Brown, Chris; Sessler, Jonathan L.

doi:10.1021/ja990734f

Cited by 61 publications

(35 citation statements)

References 21 publications

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“…It is interesting to note that, in contrast to the covalently bridged systems, a Watson± Crick base-paired donor± acceptor system is electronically weakly coupled, but nevertheless shows rather fast electron separation rates and, with only one electron transfer step, provides a long lived radical pair state [55]. Nevertheless, we believe that the covalently linked triad systems represent a good starting point for creating long lived radical pair states in model tetrad systems of covalently linked porphyrins and quinones.…”

Section: Resultsmentioning

confidence: 93%

Multifrequency time-resolved EPR (9.5GHz and 95GHz) on covalently linked porphyrin-quinone model systems for photosynthetic electron transfer: effect of molecular dynamics on electron spin polarization

Fuhs¹,

Elger²,

Möbius³

et al. 2000

Molecular Physics

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Kurreck (2000) Multifrequency time-resolved EPR (9.5GHz and 95GHz) on covalently linked porphyrin-quinone model systems for photosynthetic electron transfer: effect of molecular dynamics on electron spin polarization,Covalently linked porphyrin± quinone model systems for photosynthetic electron transfer were examined by using time-resolved electron paramagnetic resonance (TREPR) at intermediate magnetic ® eld and microwave frequency (0:34 T/9:5 GHz, X-band) and high ® eld and frequency (3:4 T/95 GHz, W-band). The paramagnetic transients studied were the light-induced spin-correlated radical pair states of the donor± acceptor complex in polar solvents below the melting point and in the soft glass phase of a liquid crystal. It is shown that the systems form strongly exchange-coupled radical pairs, whose TREPR lineshapes are determined mainly by fast electron recombination together with both spin± lattice relaxation and modulation of the exchange interaction. Below the melting point the spin± lattice relaxation rate naturally slows down, but that of the spin on the quinone site is still of the order of 10 6 s ¡1 . Most probably this is due to contributions from spin± rotation interaction, and dependent on the molecular orientation with respect to the magnetic ® eld. This relaxation anisotropy is related to anisotropic motion of the quinone site in the solvent cage. The results allow conclusions to be drawn concerning the molecular dynamics and¯exibility of the systems. To yield long-lived radical pair states that would mimic photosynthetic electron transfer, the two mechanisms described, modulation of exchange and spin± rotation interactions, have to be suppressed by reducing the molecular¯exibility of the complex.

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Section: Resultsmentioning

confidence: 93%

Multifrequency time-resolved EPR (9.5GHz and 95GHz) on covalently linked porphyrin-quinone model systems for photosynthetic electron transfer: effect of molecular dynamics on electron spin polarization

Fuhs¹,

Elger²,

Möbius³

et al. 2000

Molecular Physics

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“…The measured g-values for the two species are 2.00275 and 2.00534 for ZnP Á and DN ÁÀ respectively (from Ref. [23]). of both RP partners (Fig.…”

Section: Mechanistic Approach Of Model Photosynthesismentioning

confidence: 99%

“…In order to identify the partners of the RP and thereby clarify the origin of the SCRP signal, W-band (94 GHz) high-field EPR experiments were performed [23]. These high Zeeman fields with a much better spectral resolution allow one to clearly differentiate between the two g-factors (c) W-band TREPR spectrum of the TRP taken 250 ns after the laser pulse at 280 K in E-7.…”

Section: Mechanistic Approach Of Model Photosynthesismentioning

confidence: 99%

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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“…By varying donors and acceptors and investigating longer chain systems (for the porphyrin-quinone type systems up to two porphyrins and two quinones) one can study spin dynamics and the conditions for highly efficient electron transfer [21][22][23]. The spectra have been obtained by measuring the absorption of cwmicrowave after the laser pulse (see Fig.…”

Section: Electron Transfer and Spin Dynamics Studied By Treprmentioning

confidence: 99%

Pulsed-High Field/High-Frequency EPR Spectroscopy

Fuhs

Möbius

2002

High Magnetic Fields

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Abstract. Pulsed high-field/high-frequency electron paramagnetic resonance (EPR) spectroscopy is used to disentangle many kinds of different effects often obscured in continuous wave (cw) EPR spectra at lower magnetic fields/microwave frequencies. While the high magnetic field increases the resolution of G tensors and of nuclear Larmor frequencies, the high frequencies allow for higher time resolution for molecular dynamics as well as for transient paramagnetic intermediates studied with time-resolved EPR. Pulsed EPR methods are used for example for relaxation-time studies, and pulsed Electron Nuclear DOuble Resonance (ENDOR) is used to resolve unresolved hyperfine structure hidden in inhomogeneous linewidths. In the present article we introduce the basic concepts and selected applications to structure and mobility studies on electron transfer systems, reaction centers of photosynthesis as well as biomimetic models. The article concludes with an introduction to stochastic EPR which makes use of another concept for investigating resonance systems in order to increase the excitation bandwidth of pulsed EPR. The limited excitation bandwidth of pulses at high frequency is one of the main limitations which, so far, made Fourier transform methods hardly feasible.

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A First High-Field EPR Study of Photoinduced Electron Transfer in a Base-Paired Porphyrin−Dinitrobenzene Supramolecular Complex

Cited by 61 publications

References 21 publications

Multifrequency time-resolved EPR (9.5GHz and 95GHz) on covalently linked porphyrin-quinone model systems for photosynthetic electron transfer: effect of molecular dynamics on electron spin polarization

Multifrequency time-resolved EPR (9.5GHz and 95GHz) on covalently linked porphyrin-quinone model systems for photosynthetic electron transfer: effect of molecular dynamics on electron spin polarization

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

Pulsed-High Field/High-Frequency EPR Spectroscopy

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