title: Photoinduced electron transfer in multiporphyrinic interlocked structures: the effect of copper(I) coordination in the central site.
abstract: Photoinduced processes have been determined in a [2]catenane containing a zinc(II) porphyrin, a gold(III) porphyrin, and two free phenanthroline binding sites, Zn-Au(+), and in the corresponding copper(I) phenanthroline complex, Zn-Cu(+)-Au(+). In acetonitrile solution Zn-Au(+) is present in two different conformations: an extended one, L, which accounts for 40 % of the total, and a compact one, S. In the L conformation, the electron transfer from the excited state of the Zn porphyrin to the gold-porphyrin unit (k = 1.3x10(9) s(-1)) is followed by a slow recombination (k = 8.3x10(7) s(-1)) to the ground state. The processes in the S conformation cannot be clearly resolved but a charge-separated (CS) state is rapidly formed and decays with a lifetime on the order of fifty picoseconds. In the catenate Zn-Cu(+)-Au(+), the zinc-porphyrin excited state initially transfers energy to the Cu(I)-phenantholine unit, producing a metal-to-ligand charge-transfer (MLCT) excited state localized on the copper complex with a rate k = 1.4x10(9) s(-1). From this excited state the transfer of an electron to the gold-porphyrin unit takes place, producing the CS state Zn-Cu(2+)-Au(.), which decays with a lifetime of 10 ns. The results are discussed in comparison with the closely related [2]rotaxane, in which a further charge shift from the copper center to the zinc-porphyrin unit leads to the fully CS state. Even in the absence of such full charge separation, it is shown that the lifetimes of the CS states are increased by a factor of about 2-2.5 over those of the corresponding rotaxanes.
authors.affiliation: Istituto per la Sintesi Organica e Fotoreattivita' (ISOF), CNR, Via P. Gobetti 101, 40129 Bologna, Italy. flamigni@isof.cnr.it
authors.forename: Lucia
authors.initials: L
authors.lastname: Flamigni
authors.forename: Anna Maria
authors.initials: AM
authors.lastname: Talarico
authors.forename: Jean-Claude
authors.initials: JC
authors.lastname: Chambron
authors.forename: Valérie
authors.initials: V
authors.lastname: Heitz
authors.forename: Myriam
authors.initials: M
authors.lastname: Linke
authors.forename: Norifumi
authors.initials: N
authors.lastname: Fujita
authors.forename: Jean-Pierre
authors.initials: JP
authors.lastname: Sauvage
mesh_terms: D003300:Copper / Q000737:chemistry*; D004579:Electron Transport; D004583:Electrons; D004735:Energy Transfer; D006046:Gold / Q000737:chemistry*; D008665:Metalloporphyrins / Q000737:chemistry*; D008968:Molecular Conformation; D010777:Photochemistry; D043862:Rotaxanes / Q000737:chemistry; D013053:Spectrophotometry / Q000379:methods; D015032:Zinc / Q000737:chemistry*
chemical_list: D008665:Metalloporphyrins; D043862:Rotaxanes; D006046:Gold; D003300:Copper; D015032:Zinc