§ Shared first author(contributed equally) *
AbstractNew quinoxalinium salts 1-5 as chemosensors have been exploited via naked eye, UV-Vis absorption, fluorescence quenching and 1 H NMR experiments. New sensors 1-5 showed dual mode, nucleophilic addition and host-guest type complex towards anion (F¯, AcO¯ and ascorbate) detection. Small anions (F¯/AcO¯) showed nucleophilic addition at C2 position of quinoxalinium cation, while larger anion (ascorbate), revealed the formation of host-guest type complex due to steric hindrance posed by C3 of phenyl ring. Nucleophilic addition of small anions (F¯/AcO¯) leads to de-aromatization of quinoxalinium cation. However in the case of larger anion, ascorbate, host-guest type complex formation induces changes in absorption/fluorescence signals of quinoxalinium moiety. This selective binding has been confirmed on the basis of 1 H NMR spectroscopic technique, whereupon nucleophilic addition of small anions (F¯/AcO¯) was confirmed by monitoring characteristic proton NMR signals of H a and methylene protons (CH 2 ), which were clearly shifted in case of fluoride and acetate ions addition confirming de-aromatization and nucleophilic addition. Whereas no such peak shifting was observed in case of ascorbate ion addition confirming non-covalent addition of ascorbate.Theoretical insight into the selectivity and complexation behavior of ascorbate ion with quinoxaline moiety is gained through density functional theory (DFT) calculations. Moreover, the absorption properties of these complexes are modeled theoretically, and compared with the experimental data. In addition, thermal decomposition of sensor (1 and 2) has been studied by the means of differential scanning calorimetry (DSC), thermogravimetry (TG), and differential thermogravimetry (DTG) to signify their utility at variable temperature.