Expanding the Scope of Metastable Species in Hydrogen Bonding‐Directed Supramolecular Polymerization

We reveal unique hydrogen (H‐) bonding patterns and exploit them to control the kinetics, pathways and length of supramolecular polymers (SPs). New bisamide‐containing monomers were designed to elucidate the role of competing intra‐ vs. intermolecular H‐bonding interactions on the kinetics of supramolecular polymerization (SP). Remarkably, two polymerization‐inactive metastable states were discovered. Contrary to previous examples, the commonly assumed intramolecularly H‐bonded monomer does not evolve into intermolecularly H‐bonded SPs via ring opening, but rather forms a metastable dimer. In this dimer, all H‐bonding sites are saturated, either intra‐ or intermolecularly, hampering elongation. The dimers exhibit an advantageous preorganization, which upon opening of the intramolecular portion of the H‐bonding motif facilitates SP in a consecutive process. The retardation of spontaneous self‐assembly as a result of two metastable states enables length control in SP by seed‐mediated growth. An unprecedented mechanism for the supramolecular polymerization (SP) of H‐bonding synthons has been unravelled. Remarkably, a new on‐pathway metastable dimer state (D*) incorporating both intra‐ and intermolecular H‐bonds was discovered that allows spatiotemporal and length control of the SP through a consecutive mechanism.