Photoinduced electron transfer in multiporphyrinic interlocked structures: the effect of copper(I) coordination in the central site.
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.
Flamigni
Lucia
L
Istituto per la Sintesi Organica e Fotoreattivita' (ISOF), CNR, Via P. Gobetti 101, 40129 Bologna, Italy. flamigni@isof.cnr.it
Talarico
Anna Maria
AM
Chambron
Jean-Claude
JC
Heitz
Valérie
V
Linke
Myriam
M
Fujita
Norifumi
N
Sauvage
Jean-Pierre
JP
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*
D008665:Metalloporphyrins; D043862:Rotaxanes; D006046:Gold; D003300:Copper; D015032:Zinc