Inversion of supramolecular chirality by photo-enhanced secondary nucleation

Abstract

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.