Self-assembly of a C60 derivative bearing an ammonium unit with porphyrin-crown ether conjugates

Our recent progresses in the synthesis and the study of supramolecular porphyrin-fullerene conjugates are reported. In particular, we show that pi-stacking of the two chromophores can have a dramatic effect on recognition interactions in non-covalent C-60-porphyrin ensembles. Specifically, a supramolecular complex has been obtained from a porphyrin-crown ether conjugate and a methanofullerene derivative bearing an ammonium function. In addition to the ammonium-crown ether interaction, intramolecular stacking of the fullerene moiety and the porphyrin subunit has been evidenced in the supramolecular system. Due to this additional recognition element, the association constant (K-a) for the complex is increased by two orders of magnitude when compared to K-a values previously found for complexation of the fullerene-ammonium derivative with other crown ethers. Finally, non-covalent systems resulting from the association of the fullerene-ammonium derivative with porphyrins bearing two crown-ether subunits have been investigated. Intramolecular C-60-porphyrin interactions have also been observed within these supramolecular arrays. As a result, the 2:1 complexes are very stable. Copyright (C) 2005 Society of Porphyrins & Phthalocyanines.