A selective chemosensor and fluorescence probe for relay recognition of cations and fluoride ions in aqueous media with logic gate function.

Cation to anion relay recognition was studied for the first time with sequential specificity (Cu → F or Co → F) using a fluorescence "ON-OFF-ON" mechanism. L is a receptor with high selectivity for F, Cu and Co ions in the solution of DMSO/HO with a 9:1 vol ratio. Absorption and fluorescence spectra were used to investigate the sensing process. Fluorescent emission intensity of L at 324 is quenched (switch-Off) after the addition of Cu and Co. Surprisingly, complex L + Cu or L + Co is restored with addition of F into the compound (switch-On). Consequently, implication (from emission) and inhibit (from absorption) logic gates are constructed at molecular level. The gates operate in fluorescence and absorption modes when Cu and F or Co and F are used as input materials and the fluorescence intensity signal as outputs. Based on reversible and reproducible system, a sequential memory unit with integrated ''Writing-Reading-Erasing-Reading'' behavior, is developed.