Ring-chain morphology control in overall-neutral, internally ion-paired supramolecular polymers.

The self-assembly of internally-ion-paired neutral AA/BB-type supramolecular polymers composed of complementary di-ionizable homoditopic pairs of monomers is reported. Host-to-guest double proton transfer mediates the recognition between bis-calix[5]arene-dicarboxylic acids and α,ω-diaminoalkanes, yielding cyclic, doughnut-shaped assemblies whose morphology (i.e., cyclic vs. linear) can be controlled by means of external chemical stimuli. The behavior of these intriguing aggregates both in solution and on surface was investigated by a combination of 1H and DOSY NMR, light scattering and AFM techniques.