Modular assembly of porphyrin sandwiches as potential hosts

A zinc porphyrin dimer assembles to give a sandwich complex in the presence of 1 equiv. of the bidentate ligand DABCO. The effective molarity for cyclisation is 2 mM, so that the macrocyclic sandwich complex can be studied at μM concentrations by UV/Vis absorption spectroscopy, but at NMR concentrations, insoluble polymeric assemblies are formed. The potential of this system to function as a molecular receptor has been investigated, but the complex failed to bind a variety of aromatic substrates.