Neutral π - associated porphyrin [2]catenanes

A series of neutral porphyrin-containing catenanes has been synthesised, consisting of a zinc porphyrin strapped by apolyethylene glycol chain containing four or six ethylenoxy-units and incorporating a central naphthoquinol unit,interlinked with a naphthalene diimide macrocycle. The napthalene diimide precursor units exhibit only weakbinding with the strapped porphyrins (K[a] between 8 and 0.02 M⁻¹), but good yields of the catenanes were obtained byGlaser coupling of the alkynyl napthalene diimide precursors in the presence of the porphyrins. Structures andsolution conformations were determined by mass spectral and detailed ¹H NMR studies. For the longer strappedporphyrins, the diimide macrocycle rotates around the central naphthoquinol unit at 420–450 times per second, whilerotation is virtually prevented in the tighter strapped derivatives. A second dynamic process occurring in both sets ofcatenanes and described as ‘yawing’ leads to inequivalence in the naphthalene moieties. UV-Visible spectra indicatecharge transfer interactions and electronic communication between the two components of the catenane.