Supramolecular Complexation of Quenched Rosamines with Cucurbit[7]Uril: Fluorescence Turn-ON Effect for Super-Resolution Imaging

Here, we present a fluorogenic supramolecular host–guest system comprising cucurbit[7]uril (CB7) and a rationally designed rosamine fluorescent dye (P-ARose) tailored for super-resolution imaging applications. By strategically designing the meso-aryl moiety of the guest, we concomitantly quenched the dye’s emission in its free form and achieved strong binding with the host. The formation of the complex suppresses quenching and encompasses a large fluorescence turn-ON effect. Experimental and theoretical studies revealed that CB7 complexation significantly improved the photophysical properties of P-ARose, with a 6.4-fold fluorescence increase and 4.2-fold enhanced emission quantum yield. Further functionalization of P-ARose with a HaloTag ligand or an NHS reactive group rendered it suitable for live-cell and immunofluorescence labeling, yielding specificity, negligible background, and a minimal fluorescence signal in the unbound state. The addition of CB7 drastically increased fluorescence, enabling conventional and stimulated emission depletion (STED) imaging with subdiffraction resolution. Furthermore, the turn-ON ability of the host–guest complex facilitated pseudo two-color sequential imaging of different protein combinations within the same acquisition channel. These results demonstrate the potential of this supramolecular system to enable an additional super-resolution imaging multiplexing modality through noncovalent chemistry.