Role of the special pair in the charge-separating event in photosynthesis.
We synthesized special-pair/electron-acceptor systems consisting of a complementary slipped cofacial dimer of imidazolyl-substituted zinc porphyrin, bearing pyromellitdiimide as the electron acceptor. In the case of the dimer, the first and second oxidation potentials were split into a total of four peaks in the differential pulse voltammetry measurement. Furthermore, the shift values of the first oxidation potentials obtained by changing the solvent polarity for the dimer were almost half of those observed for the monomer. These results indicate that the radical cation is delocalized over the whole pi system of the dimer. Time-resolved transient absorption measurements revealed that, relative to the corresponding monomer, the dimer accelerated the charge separation rate, but decelerated the charge recombination rate. The smaller reorganization energy of the slipped cofacial dimer relative to that of the monomeric system demonstrates the significance of the special-pair arrangement for efficient charge separation in photosynthesis.
Ozeki
Hidekane
H
Graduate School of Materials Science, Nara Institute of Science and Technology, 8916-5 Takayama, Ikoma, Nara 630-0101, Japan.
Nomoto
Akihiro
A
Ogawa
Kazuya
K
Kobuke
Yoshiaki
Y
Murakami
Masataka
M
Hosoda
Kou
K
Ohtani
Masana
M
Nakashima
Satoru
S
Miyasaka
Hiroshi
H
Okada
Tadashi
T
D004579:Electron Transport; D048288:Imidazolines / Q000138:chemical synthesis / Q000737:chemistry; D008665:Metalloporphyrins / Q000138:chemical synthesis / Q000737:chemistry; D008958:Models, Molecular; D010788:Photosynthesis; D045322:Photosynthetic Reaction Center Complex Proteins / Q000737:chemistry
D048288:Imidazolines; D008665:Metalloporphyrins; D045322:Photosynthetic Reaction Center Complex Proteins; C017802:zinc hematoporphyrin