Recognition-Mediated Light-Up of Thiazole Orange with Cucurbit[8]uril: Exchange and Release by Chemical Stimuli

This article reports a convenient supramolecular strategy to construct fluorescent photoswitchable molecular assemblies between a macrocyclic host, cucurbit[8]uril (CB8), and a fluorogenic dye, thiazole orange (TO). The interaction mechanism and the stable stoichiometric host–guest arrangements have been claimed on the basis of the optical absorption, steady-state and time-resolved fluorescence lifetime and anisotropy measurements, and also the geometry optimization studies. The CB8 recognized TO in its 2:2 stoichiometry exhibited spectacular fluorescence enhancement of the order of 1700 fold, which is the largest directly determined value so far reported for a dye in an organic macrocyclic system. This prospective 2CB8:2TO assembly responded to selected chemical stimuli such as metal ions, adamantylamine, and tryptophan, providing different dissociation mechanisms and demonstrating a controlled exchange and release action desired with such noncovalently linked assemblies. Positively, considering the aqueous solubility and biocompatibility of the host–guest constituents, this methodology can evolve into a general approach to deliver and operate intracellularly functional molecular components under chemical/thermal/optical trigger control, especially for therapeutic applications.