A Phosphorescent Trinuclear Gold(I) Pyrazolate Chemosensor for Silver Ion Detection and Remediation in Aqueous Media.

We report a phosphorescent chemosensor based on a trinuclear Au(I) pyrazolate complex or [Au(3-CH,5-COOH)Pz] (aka AuPz) stabilized in aqueous chitosan (CS) polymer media. AuPz is synthesized in situ within aqueous CS media at pH ∼ 6.5 and room temperature (RT). AuPz exhibits strong red emission (λ ∼ 690 nm) in such solutions. On addition of silver salt to AuPz/CS aqueous media, a bright-green emissive adduct (AuPz/Ag) with a peak maximum within 475-515 nm is developed. The silver adduct exhibits a 4-fold increase in quantum yield (0.19 ± 0.02) compared to AuPz alone (0.05 ± 0.01), along with a corresponding increase in phosphorescence lifetime. With almost zero interference from 15 other metal ions tested, AuPz exhibits extreme selectivity for Ag with nM/ppb detection limits (6.4-72 ppb, depending on %CS and on the sensitivity basis being a signal-to-noise ratio (S/N) = 3 or a baseline-corrected signal change = 10%). AuPz exhibits sensitivity to higher concentrations (>1 mM) of other metal ions (Tl/Pb/Gd). The sensing methodology is simple, fast, convenient, and can even be detected by the naked eye. On addition of ethylenediaminetetraacetic acid (EDTA), the red AuPz emission can be restored. AuPz and its silver adduct retain their characteristic photophysical properties in thin film forms. Remarkable photostability with <7% photobleaching after 4 h of UV irradiation is attained for AuPz solutions or thin films.