| Summary: | The pivotal role played by potassium ions in the noncovalent synthesis of discrete porphyrin-calixarene nanostructures has been examined. The <i>flattened-cone</i> conformation adopted by the two cavities of octa-cationic calix[4]tube <b>C4T</b> was found to prevent the formation of complexes with well-defined stoichiometry between this novel water-soluble calixarene and the tetra-anionic phenylsulfonate porphyrin <b>CuTPPS</b>. Conversely, preorganization of <b>C4T</b> into a <i>C</i><sub>4v</sub>-symmetrical scaffold, triggered by potassium ion encapsulation (<b>C4T</b>@K<sup>+</sup>), allowed us to carry out an efficient hierarchical self-assembly process leading to 2D and 3D nanostructures. The stepwise formation of discrete <b>CuTPPS/C4T</b>@K<sup>+</sup> noncovalent assemblies, containing up to 33 molecular elements, was conveniently monitored by UV/vis spectroscopy by following the absorbance of the porphyrin Soret band.
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