Highly efficient coumarin-derived colorimetric chemosensors for sensitive sensing of fluoride ions and their applications in logic circuits

Abstract

In this study, three new compounds 6-substituted-3-acetylcoumarin 4-(2′-isocamphanyl)thiosemicarbazones (3a, 3b, and 3c) were facilely synthesized and employed as colorimetric chemosensors for fluoride ions. The recognition behaviors of receptors 3a, 3b, and 3c toward F– were investigated by using UV–vis absorption spectroscopy. Among them, the receptor 3c displayed more superior sensitivity and rapid response time toward F– with a swift naked-eye color change from colorless to purple, and its detection limit was as low as 6.3 × 10-7 M, and the binding constant was calculated to be 2.58 × 104 M−1. Furthermore, the interaction mechanism between the receptor 3c and F– was studied by 1H NMR, HRMS, and density functional theory (DFT) studies, suggesting that initial formation of a hydrogen-bonded host–guest complex and the subsequent deprotonation of receptor 3c upon the addition of excess F–, which was responsible for the remarkable changes in the absorption spectra of 3c. Besides, a combinatorial logic circuit of IMPLICATION and INHIBITION gates at the molecular level was fabricated using the reversibility of receptor 3c toward F– and Mg2+. Finally, the test strips coated with receptor 3c revealed a good sensitivity for F– in an aqueous medium. Apart from that, the excellent performance of receptor 3c for detecting F– was reconfirmed by grinding them with KBr powder.