Elucidation of Selectivity for Silver Ion Based on Metal-Induced H-Type Aggregation of Fluorescent Receptor

In present work, a new substituted phthalonitrile derivative was prepared by the nucleophilic displacement reaction and then highly soluble zinc phthalocyanine (ZnPc) with four peripheral 1-hydroxyhexan-3-ylthio groups was synthesized by cyclotetramerization and characterized by FTIR, ¹H and ¹³C NMRs spectroscopies, fluorescence and UV–vis measurements. The optical property and quantum yield of ZnPc were elucidated in mixed solvent of ethanol/water with varying compositions. The pH-dependent fluorescence and absorbance spectra of ZnPc in the absence and presence of Ag⁺ ions were obtained to elucidate the optimum pH value that is convenient for stable complex formation in predetermined mixture. A comparative study for recognition of Ag⁺ ion has been carried out to evaluate the effect of the solution parameters on selective sensing ability of ZnPc as a fluorescent receptor. Interference effect was investigated by spectrofluorometric titration based on fluorescence quenching of ZnPc upon addition of Ag⁺ ion in the presence of foreign metal ions. Stepwise complexation/decomplexation cycles with Na₂S-titration by fluorescence quenching/enhancement were investigated to establish the reversible response rate and reusability of ZnPc toward Ag⁺ ions.