The effect of molecular topology an
d conformation on the
dynamics of photoin
duce
d electron transfer (ET) processes has been stu
die
d in interlocke
d electron
donor鈥揳cceptor systems, specifically rotaxanes with zinc(II)-tetraphenylporphyrin (ZnP) as the electron
donor an
d [60]fullerene (C
60) as the electron acceptor. Formation or cleavage of coor
dinative bon
ds was use
d to in
duce major topological an
d conformational changes in the interlocke
d architecture. In the first approach, the tweezer-like structure create
d by the two ZnP stopper groups on the threa
d was use
d as a recognition site for complexation of 1,4-
diazabicyclo[2.2.2]octane (DABCO), which creates a bri
dge between the two ZnP moieties of the rotaxane, generating a catenane structure. The photoin
duce
d processes in the DABCO-complexe
d (ZnP)
2-[2]catenate-C
60 system were compare
d with those of the (ZnP)
2-rotaxane-C
60 precursor an
d the previously reporte
d ZnP-[2]catenate-C
60. Stea
dy-state emission an
d transient absorption stu
dies showe
d that a similar multistep ET pathway emerge
d for rotaxanes an
d catenanes upon photoexcitation at various wavelengths, ultimately resulting in a long-live
d ZnP
鈥?/C
60鈥⑩€?/sup> charge-separated radical pair (CSRP) state. However, the decay kinetics of the CSRP states clearly reflect the topological differences between the rotaxane, the catenate, and DABCO-complexed-catenate architectures. The lifetime of the long-distance ZnP鈥?鈥揫Cu(I)phen2]+鈥揅60鈥⑩€?/sup> CSRP state is more than four times longer in 3 (1.03 渭s) than in 1 (0.24 渭s) and approaches that in catenate 2 (1.1 渭s). The results clearly showed that creation of a catenane from a rotaxane topology inhibits the charge recombination process. In a second approach, when the Cu(I) ion used as the template to assemble the (ZnP)2鈥揫Cu(I)phen2]+鈥揅60 rotaxane was removed, it was evident that a major structural change had occurred. since charge separation between the chromophores was no longer observed upon photoexcitation in nonpolar as well as in polar solvents. Only ZnP and C60 triplet excited states were observed upon laser excitation of the Cu-free rotaxane. These results highlight the critical importance of the central Cu(I) ion for long-range ET processes in these nanoscale interlocked electron donor鈥揳cceptor systems.
Keywords:
d="authors" href="http://pubs.acs.org/action/doSearch?action=search&searchText=rotaxanes&qsSearchArea=searchText">rotaxanes; d="authors" href="http://pubs.acs.org/action/doSearch?action=search&searchText=catenanes&qsSearchArea=searchText">catenanes; d="authors" href="http://pubs.acs.org/action/doSearch?action=search&searchText=electron+transfer&qsSearchArea=searchText">electron transfer; d="authors" href="http://pubs.acs.org/action/doSearch?action=search&searchText=porphyrin&qsSearchArea=searchText">porphyrin; d="authors" href="http://pubs.acs.org/action/doSearch?action=search&searchText=fullerene&qsSearchArea=searchText">fullerene