Calixarenes equipped with two and four zinc porphyrins have been prepared, and they show remarkable flexibility in their self-assembly properties with the bidentate ligand DABCO. The calixbisporphyrin forms a 2:2 complex with DABCO, generating a large cavity that has the potential to act as a supramolecular host. The calix-tetraporphyrin, on the other hand, forms four different complexes with DABCO depending on the stoichiometry and concentration. During the course of a titration, all four complexes are populated, leading to large conformational changes and the formation of both intramolecular and intermolecular calix-tetraporphyrin-DABCO sandwich complexes. The system was fully characterized using a combination of UV-visible and 1H NMR spectroscopy to identify the complexes. At a calix-tetraporphyrin: DABCO ratio of 2:4, the major species is dimeric cage assembly that features a large internal cavity for guest complexation.
Molecular Acrobatics: Self-Assembly of Calixarene-Porphyrin Cages / L. BALDINI; P. BALLESTER; A. CASNATI; R. M. GOMILA; C. A. HUNTER; F. SANSONE; R. UNGARO. - In: JOURNAL OF THE AMERICAN CHEMICAL SOCIETY. - ISSN 0002-7863. - 125(2003), pp. 14181-14189. [10.1021/ja036758a]