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A coumarin-based fluorescent PET sensor utilizing supramolecular pKa shifts
Authors:Na’il Saleh  Yaseen A Al-SoudLeena Al-Kaabi  Indrajit GhoshWerner M Nau
Institution:a Department of Chemistry, UAE University, PO Box 17551, United Arab Emirates
b Department of Chemistry, University of Al al-Bayt, Al-Mafraq, Jordan
c School of Engineering and Science, Jacobs University Bremen, Campus Ring 1, D-28759 Bremen, Germany
Abstract:A new coumarin derivative containing benzothiazole and piperazine substituents was synthesized. Preferential inclusion of the benzothiazole group, over the coumarin and piperazine groups, inside the cavity of the molecular container cucurbit7]uril (CB7) was evidenced by using optical and NMR techniques. The binding constant of the new complex with CB7 is higher in its protonated forms (e.g., K = 2.8 × 106 M−1) than in its neutral forms, which led to an increase in the pKa value associated with protonation of the aza nitrogen on the benzothiazole ring of ca. 2.5 units. Such CB7-induced protonation disabled the photoinduced electron transfer (PET) in the included molecule, enhancing its coumarin fluorescence up to ca. 45-fold (pH 3.5, 410 nm). The results are discussed in the context of designing sensitive analytical tools for reversible monitoring of optically inactive analytes by competitive displacement experiments.
Keywords:Photoinduced electron transfer (PET)  pKa Shifts  Fluorescence  Sensors  Host-guest systems  Cucurbiturils  Coumarin  Benzothiazole  Piperazine
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