Tunable disruption of pseudoisocyanine J-aggregates by choline chloride-based deep eutectic solvents

Deep eutectic solvents (DESs) offer a tunable hydrogen-bonding environment capable of modulating supramolecular organization, yet their influence on cyanine dye aggregation remains largely unexplored. Here, we establish that choline chloride-based Type III DESs provide unprecedented control over the aggregation state of the prototypical J-aggregating cyanine dye pseudoisocyanine (PIC). In neat DESs, PIC remains exclusively monomeric. In contrast, incremental addition of DESs to high-ionic-strength aqueous media containing NaCl, Na₂SO₄, or KCl efficiently disassembles pre-formed J-aggregates at DES loadings of 15-30% (v/v). UV-vis and fluorescence spectroscopy reveal polarity-dependent spectral shifts, and pronounced quenching consistent with direct aggregate-to-monomer conversion. Fluorescence microscopy corroborates morphological fragmentation of the extended tubular J-aggregate domains. Molecular dynamics simulations show that the identity of the hydrogen-bond donor governs disaggregation efficiency: polyol- and sugar-based DESs engage PIC through extensive hydrogen-bonding and solvation, disrupt π-π stacking, and significantly increase aggregate root-mean-square deviation and radius of gyration, whereas a urea-based DES (Reline) produces minimal structural perturbation. Collectively, these results provide a mechanistic framework in which hydrogen-bond-mediated sequestration of counteranions and selective solvation of PIC drive aggregate destabilization. This work identifies DESs as simple, biocompatible, and highly tunable media for manipulating supramolecular dye aggregation, with fundamental implications for optical sensors, light-harvesting materials, and molecular self-assembly.