A multi-site probe for selective detection of cyanide and sulphite ions via different mechanisms with concomitant different fluorescent behaviors

Abstract

A novel organic probe (R) possessing multiple binding sites has rationally been designed, synthesized and characterized using NMR and mass spectral techniques. The probe R displays an excellent selective and sensitive response to CN– and SO32– ions over other anions. In aq. DMSO solution, R exhibits dual emission (463 and 590 nm) upon interaction with CN– ion, which is ascribed to the deprotonation of the NH group of the probe. Upon addition of SO32– ion, the enhancement of fluorescence for R at 478 nm is attributed to the formation of 1:1 adduct between R and SO32– ion by the nucleophilic addition of SO32– to C-atom of the ring CCH moiety. The fluorescence responses of R toward CN– and SO32– ions are pH independent in the 5 – 9 range. Limits of detection down to 28 and 3.7 nM were determined for CN– and SO32– quantitation, respectively. Theoretical calculations (DFT and TDDFT) are applied to interpret the absorption and dissimilar emission behaviour of the probe and its adduct with CN– and SO32– ions. The CN– induced dual fluorescence in R may be due to relaxation of the excited state to two different ground states.

Keywords

• Cyanide
• Sulphite
• Fluorescence
• Dual fluorescence
• TDDFT