Structurally-tolerant self-assembly of zinc pyridyl porphyrins

Zinc porphyrins equipped with pyridine ligands form macrocyclic assemblies in organic solvents. The assemblies have been characterised by (1)H NMR, UV-visible spectroscopy, X-ray crystallography and vapour pressure osmometry. The self-assembly properties of six isomeric porphyrins are relatively insensitive to the geometry of the porphyrin monomer. Changes in the internal torsion angles allow all of the porphyrins to form macrocyclic dimers but with differences in the relative orientations of the porphyrin units. The associated strain reduces the effective molarities from the value of 6 M reported previously for an 'ideal' monomer to between 0.07 and 2 M leading to dimerisation constants in the 10(5)-10(6) M(-1) range. Only one isomer has a geometry that makes dimerisation impossible without severe distortion, and this compound self-assembles to give a tetrameric macrocycle at millimolar concentrations.