Thermoreversible Polymorph Transitions in Supramolecular Polymers of Hydrogen‐Bonded Squaramides

Hydrogen‐bonded squaramide (SQ) supramolecular polymers exhibit uncommon thermoreversible polymorph transitions between particle‐ and fiber‐like nanostructures. SQs 1–3, with different steric bulk, self‐assemble in solution into particles (AggI) upon cooling to 298 K, and SQs 1 and 2, with only one dendronic group, show a reversible transformation into fibers (AggII) by further decreasing the temperature to 288 K. Nano‐DSC and UV/Vis studies on SQ 1 reveal a concentration‐dependent transition temperature and ΔH for the AggI‐to‐AggII conversion, while the kinetic studies on SQ 2 indicate the on‐pathway nature of the polymorph transition. Spectroscopic and theoretical studies reveal that these transitions are triggered by the molecular reorganization of the SQ units changing from slipped to head‐to‐tail hydrogen bonding patterns. This work unveils the thermodynamic and kinetic aspects of reversible polymorph transitions that are of interest to develop stimuli‐responsive systems.