A combination of experimental and TD-DFT investigations on the fluorescent detection of sulfite and bisulfite ions in aqueous solution via nucleophilic addition reaction

The selective detection of sulfite and bisulfite ions with anthracene-based compounds (CN1 and CN2) as chemodosimeters is reported using fluorescence changes in DMSO:HEPES (70:30%), v/v buffer solution (pH 7.4). Upon treatment with sulfite and bisulfite ions, the fluorescence of the probes gets enhanced significantly at 424 nm. The detection of these ions occurs through the nucleophilic addition at the vinylic C-atom of the probes, which terminates the photo-induced electron transfer (PET) process and consequently enhances the fluorescence. This detection mechanism is well supported by 1H NMR titration, HR-MS and DFT/TD-DFT calculations. The pseudofirst-order rate constants for the addition sulfite (at pH 7.4) and bisulfite (at pH 5) to CN1 are determined to be 3.22x10-3 and 5.02x10-3 s-1, respectively. The limits of detection for sulfite and bisulfite are found to be 1.85x10-7 and 1.56x10-7 M, respectively. The probe CN1 was successfully applied to the detection of bisulfite ion in real samples.

Automated summary

Selective detection of sulfite and bisulfite ions using anthracene-based compounds as chemodosimeters is achieved through nucleophilic addition and termination of PET process. The detection mechanism is supported by various analytical techniques, and the probe shows promising results in real sample analysis.