Photochemistry of artificial photosynthetic reaction centers in liquid crystals probed by multifrequency EPR (9.5 and 95 GHz)

Marilena Di Valentin, Arianna Bisol, Giancarlo Agostini, Michael Fuhs, Paul A. Liddell, Ana L Moore, Thomas A Moore, John Devens Gust, Donatella Carbonera

Research output: Contribution to journalArticle

29 Citations (Scopus)

Abstract

Photoinduced charge separation and recombination in a carotenoid-porphyrin- fullerene triad C-P-C601 have been followed by multifrequency time-resolved electron paramagnetic resonance (TREPR) at intermediate magnetic field and microwave frequency (X-band) and high field and frequency (W-band). The electron-transfer process has been characterized in the different phases of two uniaxial liquid crystals (E-7 and ZLI-1167). The triad undergoes photoinduced electron transfer, with the generation of a long-lived charge-separated state, and charge recombination to the triplet state, localized in the carotene moiety, mimicking different aspects of the photosynthetic electron-transfer process. Both the photoinduced spin-correlated radical pair and the spin-polarized recombination triplet are observed starting from the crystalline up to the isotropic phase of the liquid crystals. The W-band TREPR radical pair spectrum has allowed unambiguous assignment of the spin-correlated radical pair spectrum to the charge-separated state C•+-P-C 60•-. The magnetic interaction parameters have been evaluated by simulation of the spin-polarized radical pair spectrum and the spin-selective recombination rates have been derived from the time dependence of the spectrum. The weak exchange interaction parameter (J = +0.5 ± 0.2 G) provides a direct measure of the dominant electronic coupling matrix element V between the C•+-P-C60•- radical pair state and the recombination triplet state 3C-P-C60. The kinetic parameters have been analyzed in terms of the effect of the liquid crystal medium on the electron-transfer process. Effects of orientation of the molecular triad in the liquid crystal are evidenced by simulations of the carotenoid triplet state EPR spectra at different orientations of the external magnetic field with respect to the director of the mesophase. The order parameter (S = 0.5 ± 0.05) has been evaluated.

Original languageEnglish
Pages (from-to)17074-17086
Number of pages13
JournalJournal of the American Chemical Society
Volume126
Issue number51
DOIs
Publication statusPublished - Dec 29 2004

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Photosynthetic Reaction Center Complex Proteins
Photochemistry
Liquid Crystals
Photochemical reactions
Liquid crystals
Genetic Recombination
Paramagnetic resonance
Carotenoids
Electrons
Electron Spin Resonance Spectroscopy
Magnetic Fields
Magnetic fields
Fullerenes
Microwave frequencies
Exchange interactions
Porphyrins
Kinetic parameters
Crystal orientation
Frequency bands
Microwaves

ASJC Scopus subject areas

  • Chemistry(all)

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Photochemistry of artificial photosynthetic reaction centers in liquid crystals probed by multifrequency EPR (9.5 and 95 GHz). / Di Valentin, Marilena; Bisol, Arianna; Agostini, Giancarlo; Fuhs, Michael; Liddell, Paul A.; Moore, Ana L; Moore, Thomas A; Gust, John Devens; Carbonera, Donatella.

In: Journal of the American Chemical Society, Vol. 126, No. 51, 29.12.2004, p. 17074-17086.

Research output: Contribution to journalArticle

Di Valentin, Marilena ; Bisol, Arianna ; Agostini, Giancarlo ; Fuhs, Michael ; Liddell, Paul A. ; Moore, Ana L ; Moore, Thomas A ; Gust, John Devens ; Carbonera, Donatella. / Photochemistry of artificial photosynthetic reaction centers in liquid crystals probed by multifrequency EPR (9.5 and 95 GHz). In: Journal of the American Chemical Society. 2004 ; Vol. 126, No. 51. pp. 17074-17086.
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abstract = "Photoinduced charge separation and recombination in a carotenoid-porphyrin- fullerene triad C-P-C601 have been followed by multifrequency time-resolved electron paramagnetic resonance (TREPR) at intermediate magnetic field and microwave frequency (X-band) and high field and frequency (W-band). The electron-transfer process has been characterized in the different phases of two uniaxial liquid crystals (E-7 and ZLI-1167). The triad undergoes photoinduced electron transfer, with the generation of a long-lived charge-separated state, and charge recombination to the triplet state, localized in the carotene moiety, mimicking different aspects of the photosynthetic electron-transfer process. Both the photoinduced spin-correlated radical pair and the spin-polarized recombination triplet are observed starting from the crystalline up to the isotropic phase of the liquid crystals. The W-band TREPR radical pair spectrum has allowed unambiguous assignment of the spin-correlated radical pair spectrum to the charge-separated state C•+-P-C 60•-. The magnetic interaction parameters have been evaluated by simulation of the spin-polarized radical pair spectrum and the spin-selective recombination rates have been derived from the time dependence of the spectrum. The weak exchange interaction parameter (J = +0.5 ± 0.2 G) provides a direct measure of the dominant electronic coupling matrix element V between the C•+-P-C60•- radical pair state and the recombination triplet state 3C-P-C60. The kinetic parameters have been analyzed in terms of the effect of the liquid crystal medium on the electron-transfer process. Effects of orientation of the molecular triad in the liquid crystal are evidenced by simulations of the carotenoid triplet state EPR spectra at different orientations of the external magnetic field with respect to the director of the mesophase. The order parameter (S = 0.5 ± 0.05) has been evaluated.",
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T1 - Photochemistry of artificial photosynthetic reaction centers in liquid crystals probed by multifrequency EPR (9.5 and 95 GHz)

AU - Di Valentin, Marilena

AU - Bisol, Arianna

AU - Agostini, Giancarlo

AU - Fuhs, Michael

AU - Liddell, Paul A.

AU - Moore, Ana L

AU - Moore, Thomas A

AU - Gust, John Devens

AU - Carbonera, Donatella

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AB - Photoinduced charge separation and recombination in a carotenoid-porphyrin- fullerene triad C-P-C601 have been followed by multifrequency time-resolved electron paramagnetic resonance (TREPR) at intermediate magnetic field and microwave frequency (X-band) and high field and frequency (W-band). The electron-transfer process has been characterized in the different phases of two uniaxial liquid crystals (E-7 and ZLI-1167). The triad undergoes photoinduced electron transfer, with the generation of a long-lived charge-separated state, and charge recombination to the triplet state, localized in the carotene moiety, mimicking different aspects of the photosynthetic electron-transfer process. Both the photoinduced spin-correlated radical pair and the spin-polarized recombination triplet are observed starting from the crystalline up to the isotropic phase of the liquid crystals. The W-band TREPR radical pair spectrum has allowed unambiguous assignment of the spin-correlated radical pair spectrum to the charge-separated state C•+-P-C 60•-. The magnetic interaction parameters have been evaluated by simulation of the spin-polarized radical pair spectrum and the spin-selective recombination rates have been derived from the time dependence of the spectrum. The weak exchange interaction parameter (J = +0.5 ± 0.2 G) provides a direct measure of the dominant electronic coupling matrix element V between the C•+-P-C60•- radical pair state and the recombination triplet state 3C-P-C60. The kinetic parameters have been analyzed in terms of the effect of the liquid crystal medium on the electron-transfer process. Effects of orientation of the molecular triad in the liquid crystal are evidenced by simulations of the carotenoid triplet state EPR spectra at different orientations of the external magnetic field with respect to the director of the mesophase. The order parameter (S = 0.5 ± 0.05) has been evaluated.

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