Thermally Controlled Chiral Supramolecular Polymorphism in Water.

Biological assemblies such as proteins adapt their helical morphology and function in response to external stimuli, yet controlled polymorphic transitions in synthetic chiral supramolecular analogues remain poorly understood. Herein, we demonstrate a strategy to achieve controlled chiral supramolecular polymorphism in water by coupling molecular design with external stimuli. An unsymmetrical oligo(phenyleneethynylene) derivative 1 bearing a pyridine unit, a hydrogen-bonding amide group, and chiral hydrophilic side chains self-assembles into three distinct chiral supramolecular polymorphs in water that are stable at different temperature regimes. At room temperature (RT), 1 self-assembles into short cylinders (AggI), which undergo a polymorphic transition to transient double helical fibers upon heating around the LCST (AggII, ≈ 325 K) and ultimately to irregular planar aggregates (AggIII) above the LCST. Remarkably, the polymorphic transitions are linked to the temperature-dependent conformation and degree of dehydration of the glycol chains. Although AggII exists only within a narrow temperature window in pristine water, it can be stabilized and isolated at RT through chemical stimuli such as co-solvents or metal salts that modulate the LCST. Our results establish LCST-coupled chirality as a powerful strategy to regulate thermoresponsive supramolecular polymorphism and offer potential strategies for the design of adaptive materials.