Energy Transfer in a Supramolecular Complex Assembled via Sapphyrin Dimer-mediated Dicarboxylate Anion Chelation

The synthesis of a new terephthalate-strapped porphyrin is described. This porphyrin, prepared in the form of the free base and corresponding zinc(II) complex, was designed to act as the photo-donor portion of a novel, non-covalent artificial light-harvesting complex, the other, acceptor component of which is comprised of a covalently linked sapphyrin dimer. UV-vis and 1 H NMR spectroscopic analyses were used to establish that strong complexes are formed between the porphyrin terephthalate and sapphyrin dimer components (affinity constants on the order of 105 M−1 in dichloromethane). In these complexes the dicarboxylate portion of the strapped porphyrin is sandwiched between two sapphyrins of an individual dimer. Steady state fluorescence studies of the resulting ensembles support the conclusion that, upon photoexcitation of the porphyrin subunit, energy transfer from the porphyrin to the sapphyrin dimer occurs efficiently. This intra-ensemble, anion-chelation-based energy transfer can be inhibited by the addition of fluoride anion.