Porphyrin dyads linked by a rotatable 3,3'-biphenyl scaffold: a new binding motif for small ditopic molecules.

Synthetic access to a set of metallo- and free base bis-porphyrins has been provided by a stepwise approach involving sequential peptide and Suzuki couplings. Linking these porphyrins through a 3,3'-biphenyl bridge enables cooperative binding to ditopic ligands such as the bipyridyls. Association constants and binding stoichiometry has been determined by spectroscopic/spectrophotometric means and the differences in the binding affinities of a small series of diaza ligands is discussed in the context of structural fit and microscopic association constants.