Design of a fluorescent dye for indicator displacement from cucurbiturils:: A macrocycle-responsive fluorescent switch operating through a pKa shift

The derivatization of 3-amino-9-ethylcarbazole with a diamino-alkyl anchor affords a fluorescent dye suitable for indicator displacement from cucurbituril macrocycles. The novel compound 1 shows, due to a complexation-induced pK(a) shift, a large and predictable dual fluorescence response (100-fold increase at 375 nm and 9-fold decrease at 458 nm) upon supramolecular encapsulation and a strong affinity for cation-receptor macrocycles, in particular cucurbit[6]uril (06). A direct application is presented by monitoring the enzymatic activity of lysine decarboxylase.