Pathway Complexity in Supramolecular Copolymerization and Blocky Star Copolymers by a Hetero-Seeding Effect

Abstract

This study unravels the intricate kinetic and thermodynamic pathways involved in the supramolecular copolymerization of the two chiral dipolar naphthalene monoimide (NMI) building blocks (<b>O-NMI</b> and <b>S-NMI</b>), differing merely by a single heteroatom (oxygen vs sulfur). <b>O-NMI</b> exhibits distinct supramolecular polymerization features as compared to <b>S-NMI</b> in terms of its pathway complexity, hierarchical organization, and chiroptical properties. Two distinct self-assembly pathways in <b>O-NMI</b> occur due to the interplay between the competing dipolar interactions among the NMI chromophores and amide-amide hydrogen (H)-bonding that engenders distinct nanotapes and helical fibers, from its antiparallel and parallel stacking modes, respectively. In contrast, the propensity of <b>S-NMI</b> to form only a stable spherical assembly is ascribed to its much stronger amide-amide H-bonding, which outperforms other competing interactions. Under the thermodynamic route, an equimolar mixture of the two monomers generates a temporally controlled chiral statistical supramolecular copolymer that autocatalytically evolves from an initially formed metastable spherical heterostructure. In contrast, the sequence-controlled addition of the two monomers leads to the kinetically driven hetero-seeded block copolymerization. The ability to trap <b>O-NMI</b> in a metastable state allows its secondary nucleation from the surface of the thermodynamically stable <b>S-NMI</b> spherical "seed", which leads to the core-multiarmed "star" copolymer with reversibly and temporally controllable length of the growing <b>O-NMI</b> "arms" from the <b>S-NMI</b> "core". Unlike the one-dimensional self-assembly of <b>O-NMI</b> and its random co-assembly with <b>S-NMI</b>, which are both chiral, unprecedentedly, the preferred helical bias of the nucleating <b>O-NMI</b> fibers is completely inhibited by the absence of stereoregularity of the <b>S-NMI</b> "seed" in the "star" topology.