A reversible fluorescence “ON–OFF–ON” sensor for sequential detection of F− and Cu2+ ions and its application as a molecular-scale logic device and security keypad lock

Abstract

A new azoimine receptor, R1, was synthesized by Schiff base condensation of 4-(4-butylphenyl) azophenol and 2,6-diaminopyridine and acts as a colorimetric and fluorometric chemosensor for F− and also toward Cu2+ ions in aqueous environment. UV–Vis absorption and fluorescent emission spectra were employed to study the sensing process. Emission study was performed to examine the dual sensing ability of the obtained probe with sequential addition of F− followed by Cu2+ and vice versa. The receptor is an efficient “ON–OFF” fluorescent probe for the fluoride ion. Also, R1 + F− operated as an “OFF–ON” fluorescent sensor for Cu2+ ions. Considering emission intensity and absorption wavelength for F− and Cu2+ ions, a molecular system was developed with the ability to mimic the functions of XNOR logic gating on the molecular level. In addition, R1 behaved as a molecular security keypad lock with F− and Cu2+ inputs. The keypad lock operation is particularly important, as the output of the system depends not only on the proper combination but also on the order of input signals, creating the correct password that can be used to “open” this molecular keypad lock through strong fluorescence emission at 460 nm.