Inversion of supramolecular chirality by photo-enhanced secondary nucleation

Understanding how molecules in solution begin to nucleate and grow into defined aggregates remains an outstanding mechanistic challenge. This is because the nucleation process is affected by a number of physicochemical factors that act simultaneously and whose individual contributions are hard to disentangle. Here, we demonstrate how residual aggregates in a molecular dispersion state affect the nucleation kinetics and the resulting self-assembly pathway. Using the photoisomerization of a chiral azobenzene molecule, the amounts of residual aggregates can be controlled in the pre-assembly supersaturated solution. The residual aggregates induce surface-catalysed secondary nucleation of monomers, affecting the chiral intermolecular configuration during self-assembly to afford metastable right-handed P-aggregates as opposed to thermodynamically stable left-handed M-aggregates. By exploiting the photoisomerization process, we establish high-fidelity control over the nucleation processes and demonstrate reversible M ⇄ off ⇄ P tristate switching of supramolecular chirality. Finally, we show that chiral aggregates exhibit opposite chirality-induced spin selectivities with high spin-polarization rates.