[2]Catenanes Decorated with Porphyrin and [60]Fullerene Groups: Design, Convergent Synthesis, and Photoinduced Processes

A new class of [2]catenanes containing zinc(II)-porphyrin (ZnP) and/or [60]fullerene (C-60) as appended groups has been prepared. A complete description of the convergent synthetic approach based on Cu(I) template methodology and "click" 1,3-dipolar cycloaddition chemistry is described. This new electron donor-acceptor catenane family has been subjected to extensive spectroscopic, computational, electrochemical and photophysical studies. H-1 NMR spectroscopy and computational analysis have revealed that the ZnP-C-60-[2]catenane adopts an extended conformation with the chromophores as far as possible from each other. A detailed photophysical investigation has revealed that upon irradiation the ZnP singlet excited state initially transfers energy to the (phenanthroline)(2)-Cu(I) complex core, producing a metal-to-ligand charge transfer (MLCT) excited state, which in turn transfers an electron to the C-60 group, generating the ZnP-[Cu(phen)(2)](2+)-C-60(center dot-) charge-separated state. A further charge shift from the (Cu(phen)(2)](2+) complex to the ZnP subunit, competitive with decay to the ground state, leads to the isoenergetic long distance ZnP center dot+-[Cu(phen)(2)](+)-C-60(center dot-) charge-separated radical pair state, which slowly decays back to the ground state on the microsecond time scale. The slow rate of back-electron transfer indicates that in this interlocked system, as in previously studied covalently linked ZnP-C-60 hybrid materials, this process occurs in the Marcus-inverted region.