TY - JOUR
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
AU - Moore, Thomas
AU - Gust, Devens
AU - Carbonera, Donatella
PY - 2004/12/29
Y1 - 2004/12/29
N2 - 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.
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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U2 - 10.1021/ja046067u
DO - 10.1021/ja046067u
M3 - Article
C2 - 15612747
AN - SCOPUS:11244258351
SN - 0002-7863
VL - 126
SP - 17074
EP - 17086
JO - Journal of the American Chemical Society
JF - Journal of the American Chemical Society
IS - 51
ER -