Abstract: We report the synthesis of the chiral benzotrithiophene (BTT) derivative 1, which self-assembles into helical supramolecular polymers. The C3 symmetry of BTT 1 enables a unique temperature-dependent stereomutation process in which water acts as a key effector. Circular dichroism measurements reveal that a higher water content induces a double stereomutation, ultimately restoring the original helicity. In contrast, reducing the water content leads to a single, stable stereomutation, which duration depends on the amount of water in solution. To elucidate the stereomutation mechanism, we conducted a multi-level computational study, identifying two main conformations for the monomeric species that lead to diastereomeric helices with different preferred handedness, thus resulting in opposite dichroic patterns. The transition between these aggregates involves rotation of the BTT cores and amide groups, a process significantly facilitated by water molecules via triple hydrogen bonding within the helical stack.These findings exhibit the crucial role of the solvent in modulating chiral supramolecular polymer structures and provide unprecedented insights into the influence of water on self-assembly and stereomutation processes.

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