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 1 H NMR, IR, ESI-MS and 13 C 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. 1 H 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. Graphic abstract 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.