A fluorescent bis-NBD derivative of calix[4]arene: Switchable response to Ag+ and HCHO in solution phase

A bis-nitrobenzoxadiazole (NBD) derivative of calix[4]arene (L 1 ) and a control compound (L 2 ), mono-NBD derivative of the calixarene were designed and prepared via click chemistry. Fluorescence studies demonstrated that L 1 as created can function as a switch with the presence of Ag + in THF, of which the free state of L 1 emits at ∼527   nm, but the binding state at 576   nm. Based upon this discovery, L 1 was studied as a chemo-sensor of Ag + in a mixture solvent of THF and H 2 O with a detection limit (DL) of ∼6.2   ×   10 −7   mol/L. Presence of other commonly found metal ions shows little effect upon the determination. Moreover, the L 1 in the Ag + -L 1 complex could be fully released with introduction of HCHO, a bases for the sensitive and selective detection of the toxic chemical. The DL of this test is 6.6   ×   10 −7   mol/L. Interestingly, binding and releasing of the fluorescent ligand could be repeated for at least 5 times. Furthermore, both sensing could be performed in a visualized manner. It is believed that the fluorescent compound as created should have a potential to find real-life applications.