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Photoinduced Electron Transfer in Multiporphyrinic Interlocked Structures: The Effect of Copper( I ) Coordination in the Central Site
Author(s) -
Flamigni Lucia,
Talarico Anna Maria,
Chambron JeanClaude,
Heitz Valérie,
Linke Myriam,
Fujita Norifumi,
Sauvage JeanPierre
Publication year - 2004
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.200305655
Subject(s) - porphyrin , chemistry , excited state , copper , electron transfer , zinc , crystallography , photochemistry , photoinduced electron transfer , ligand (biochemistry) , metal , atomic physics , organic chemistry , biochemistry , physics , receptor
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 = 1.3×10 9 s −1 ) is followed by a slow recombination ( k = 8.3×10 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 = 1.4×10 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.