Photochemistry of Artificial Photosynthetic Reaction Centers in Liquid Crystals Probed by Multifrequency EPR (9.5 and 95 GHz)
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- 作者：Marilena Di Valentin ; Arianna Bisol ; Giancarlo Agostini ; Michael Fuhs ; Paul A. Liddell ; Ana L. Moore ; Thomas A. Moore ; Devens Gust ; and Donatella Carbonera
- 刊名：Journal of the American Chemical Society
- 出版年：2004
- 出版时间：December 29, 2004
- 年：2004
- 卷：126
- 期：51
- 页码：17074 - 17086
- 全文大小：198K
- 年卷期：v.126,no.51(December 29, 2004)
- ISSN：1520-5126
文摘
Photoinduced charge separation and recombination in a carotenoid-porphyrin-fullerene triadC-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 crystallineup to the isotropic phase of the liquid crystals. The W-band TREPR radical pair spectrum has allowedunambiguous assignment of the spin-correlated radical pair spectrum to the charge-separated state C
+-P-C60-. The magnetic interaction parameters have been evaluated by simulation of the spin-polarizedradical pair spectrum and the spin-selective recombination rates have been derived from the timedependence of the spectrum. The weak exchange interaction parameter (J = +0.5 ± 0.2 G) provides adirect measure of the dominant electronic coupling matrix element V between the C+-P-C60- radicalpair state and the recombination triplet state 3C-P-C60. The kinetic parameters have been analyzed interms of the effect of the liquid crystal medium on the electron-transfer process. Effects of orientation ofthe molecular triad in the liquid crystal are evidenced by simulations of the carotenoid triplet state EPRspectra 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.
+-P-C60-. The magnetic interaction parameters have been evaluated by simulation of the spin-polarizedradical pair spectrum and the spin-selective recombination rates have been derived from the timedependence of the spectrum. The weak exchange interaction parameter (J = +0.5 ± 0.2 G) provides adirect measure of the dominant electronic coupling matrix element V between the C+-P-C60- radicalpair state and the recombination triplet state 3C-P-C60. The kinetic parameters have been analyzed interms of the effect of the liquid crystal medium on the electron-transfer process. Effects of orientation ofthe molecular triad in the liquid crystal are evidenced by simulations of the carotenoid triplet state EPRspectra 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.