Kinetic Control and Trapping in the Supramolecular Polymerization of m-Terphenyl Bis-Urea Macrocycles.

Abstract

Herein, we examine pathway complexity in the supramolecular polymerization of a novel m-terphenyl bis-urea macrocycle. Designed to induce kinetically metastable states, the macrocycle's concentration-dependent aggregation was studied via ¹H NMR and IR spectroscopy in THF and CHCl₃. Temperature-dependent UV-Vis spectroscopy in water/THF revealed a cooperative nucleation-growth mechanism, indicated by a shift in λmax to longer wavelengths upon cooling. Morphological studies using DLS, AFM, and SEM demonstrated fibrous aggregate formation. Thermal hysteresis observed in assembly-disassembly cycles indicated kinetically trapped species, with cooling governed by kinetic control and heating by thermodynamic processes. Deviations in ΔH values during cooling, compared to van't Hoff analysis and alignment of heating ΔH values with thermodynamic predictions, reinforced this distinction. Spontaneous nucleation retardation, resulting from monomer trapping, led to lag times of up to 50 minutes under specific conditions. Computational studies revealed parallel urea conformation as the more stable monomer configuration, whereas the antiparallel conformation is more stable in dimers. By probing pathway complexity of the macrocycle, we demonstrate a distinct ability to control and stabilize kinetically trapped states, broadening the scope for designing macrocyclic supramolecular polymers with tailored properties. This work deepens our understanding of supramolecular dynamics, exploring ON-pathway mechanisms and advancing tunable supramolecular materials.