Hierarchical Mesoscale Trapping Controls Pathway Selection in Supramolecular Polymerization.

Supramolecular polymerization often proceeds through competing kinetic and thermodynamic pathways, giving rise to pathway complexity that governs the structure and function of supramolecular materials. While pathway selection is typically interpreted in terms of molecular packing, the potential regulatory role of organization beyond the molecular scale remains largely unexplored. Here we demonstrate that hierarchical mesoscale aggregation can control pathway selection during supramolecular polymerization. A donor-acceptor dicyanostilbene derivative forms two primary aggregates that further assemble into mesoscale structures under concentrated conditions. Time-resolved small-angle x-ray scattering combined with spectroscopy reveals that mesoscale clusters transiently trap metastable assemblies, thereby delaying their conversion into thermodynamically favored fibers. Increasing temperature enables escape from this mesoscale trap, directly switching the assembly pathway. These findings identify mesoscale trapping as an emergent kinetic regulatory mechanism in supramolecular polymerization.