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

Abstract

A new class of [2]catenanes containing zinc(II)−porphyrin (ZnP) and/or [60]fullerene (C₆₀) 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. ¹H NMR spectroscopy and computational analysis have revealed that the ZnP−C₆₀−[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 C₆₀ group, generating the ZnP−[Cu(phen)₂]²⁺−C₆₀^•− 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^•+−[Cu(phen)₂]⁺−C₆₀^•− 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−C₆₀ hybrid materials, this process occurs in the Marcus-inverted region.