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 (L1) and a control compound (L2), mono-NBD derivative of the calixarene were designed and prepared via click chemistry. Fluorescence studies demonstrated that L1 as created can function as a switch with the presence of Ag+ in THF, of which the free state of L1 emits at ∼527 nm, but the binding state at 576 nm. Based upon this discovery, L1 was studied as a chemo-sensor of Ag+ in a mixture solvent of THF and H2O 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 L1 in the Ag+-L1 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.