title: Role of the special pair in the charge-separating event in photosynthesis.
abstract: 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.
authors.affiliation: Graduate School of Materials Science, Nara Institute of Science and Technology, 8916-5 Takayama, Ikoma, Nara 630-0101, Japan.
authors.forename: Hidekane
authors.initials: H
authors.lastname: Ozeki
authors.forename: Akihiro
authors.initials: A
authors.lastname: Nomoto
authors.forename: Kazuya
authors.initials: K
authors.lastname: Ogawa
authors.forename: Yoshiaki
authors.initials: Y
authors.lastname: Kobuke
authors.forename: Masataka
authors.initials: M
authors.lastname: Murakami
authors.forename: Kou
authors.initials: K
authors.lastname: Hosoda
authors.forename: Masana
authors.initials: M
authors.lastname: Ohtani
authors.forename: Satoru
authors.initials: S
authors.lastname: Nakashima
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Miyasaka
authors.forename: Tadashi
authors.initials: T
authors.lastname: Okada
mesh_terms: 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
chemical_list: D048288:Imidazolines; D008665:Metalloporphyrins; D045322:Photosynthetic Reaction Center Complex Proteins; C017802:zinc hematoporphyrin