Fluorescence enhancement of cationic styrylcoumarin-cucurbit[7]uril complexes: Enhanced stability and cellular membrane localization

Two red-emitting water-soluble fluorophores bearing a coumarin scaffold were synthesized and their interactions with cucurbit[7]uril [CB7] were investigated. A significant red-shift in the absorption spectra showed the interaction of coumarin dyes with the carbonyl portals of CB[7]. The formation of supramolecular complex is substantiated by the chemical shift changes in ¹H-NMR and the thermodynamic parameters were evaluated by isothermal calorimetric titration (ITC). Upon encapsulation with the non-fluorescent CB host, significant enhancement of fluorescence quantum efficiency is observed. The large modulation of the emission properties of fluorophores in the presence of CB[7] indicates the formation of supramolecular complex. The advantageous enhanced quantum efficiency of the CB-dye complexes, is utilized to image live cells revealing localization in cellular membranes with greater photostability. These results based on inclusion complexes of the coumarin fluorophores with a non-toxic host CB[7] could lead to the design of efficient biological probes.