Imine-Based Transient Supramolecular Polymers

Systems that change properties upon exposure to chemical stimuli offer the interesting prospect of (partially) mimicking the functions of living systems. Over the past decade, numerous supramolecular systems whose chemical composition and properties are regulated by the dissipation of chemical fuels have been reported. These systems are typically based on the transient transformation of a "dormant" species into an active, self-assembling supramolecular monomer. The process is powered by fuel consumption and terminates upon fuel depletion, restoring the initial dormant state. Previously reported out-of-equilibrium supramolecular polymerizations relied on the activation of the dormant species by adding or removing small structural units to enable supramolecular polymerization. Here, we present an approach that combines the reversibility of dynamic covalent chemistry and supramolecular chemistry to trigger transient supramolecular polymerizations by "recycling" the components of a dynamic combinatorial library (DCL). Treatment of an equilibrated DCL of aliphatic imines and aromatic amines with an activated carboxylic acid (ACA) generates a dissipative dynamic combinatorial library of aromatic imines and protonated aliphatic amines. The transient acidic conditions enable the creation of a supramolecular polymer held together by interactions between the protonated aliphatic amines and the crown ether moieties embedded in the scaffold of the aromatic imines. Thus, fuel dissipation reshuffles the chemical connectivity and enables the temporary transformation of a purely covalent (polymeric) system into a supramolecular polymer. We demonstrate the strategy using two different covalent dormant feedstocks consisting of a diimine macrocycle involving a calix[4]arene scaffold and a distribution of imine (cyclo)oligomers derived from an isophthalaldehyde skeleton.