Self-assembly dynamics of modular homoditopic bis-calix[5]arenes and long-chain alpha,omega-alkanediyldiammonium components

Homoditopic building blocks 1, featuring two π-rich cone-like calix[5]arene moieties connected at their narrow rims by a rigid o-, m-, or p-xylyl spacer in a centrosymmetric divergent arrangement, show a remarkable tendency to spontaneously and reversibly self-assemble with the complementary homoditopic α,ω-alkanediyldiammonium dipicrate guest salts C8−C12·2Pic through iterative intermolecular inclusion events, forming supramolecular assemblies whose composition and dynamics strongly depend upon the length of the connector, the geometry of the spacer, as well as the concentration and/or molar ratios between the two components. 1H NMR spectroscopy and ESI-MS studies of 1/Cn·2Pic modular homoditopic pairs support the formation of discrete (bis)-endo-cavity assemblies with the shorter C8 and C9 connectors, and/or (poly)capsular assemblies with the longer C10−C12 components under appropriate concentrations and molar ratios (50 mM equimolar solutions). 1H NMR titration experiments and diffusion NMR studies provide clear evidence for the self-assembly dynamics of the complementary pairs here investigated.