A highly selective anthraquinone appended oxacalixarene receptor for fluorescent ICT sensing of F − ions: an experimental and computational study

A new anthraquinone appended oxacalix[4]arene (DAQOC) has been synthesized and characterized by different 1H NMR, IR, ESI-MS and 13C NMR spectroscopic techniques. This compound was explored for its sensing abilities towards various anions. DAQOC showed selective anion sensing behaviour towards F− ions which was supported by absorption as well as emission studies. Among other anions, only in the presence of F− ions, a quenching in the fluorescence emission of over 79% was observed due to changes in the intermolecular charge transfer (ICT) process. DAQOC exhibited high selectivity and good sensitivity toward F− ions in the presence of competing ions and the detection limit was found to be 1.23 µM. 1H NMR titration displays that the peak corresponding to –NH protons (at 12.91 ppm) disappears upon interaction with F−, suggesting that the sensing mechanism follows the deprotonation route. The geometrical features of F− bound oxacalixarene species were modelled by the Density Functional Theory (DFT) and NCIPlot calculations. The findings suggested that the appended substituents including nitro groups and anthraquinone can make the calix[4]arene ring electron deficient and thereby more susceptible for F− ions. Moreover, this present chemosensor has been applied for recognition of F− ions from waste water samples which is of direct practical relevance. A new anthraquinone appended oxacalix[4]arene has been explored for its sensing abilities towards F− by absorption and emission studies. An intermolecular charge transfer mechanism has been attributed due to the deprotonation of N–H groups in DAQOC. DAQOC-F− complex is modelled by the Density Functional Theory and NCIPlot calculations.