Thiophene-Substituted Pyrogallol[4]arene Macrocycle and Its Application in Selective Mercury Sensing via Silver Nanoparticle Complexation

A novel thiophene-substituted pyrogallol[4]arene (Pg 4 THP 4 ) derivative was synthesized and thoroughly characterized by using 1 H NMR, MALDI-TOF MS, and single-crystal X-ray diffraction (SC-XRD) analyses. Additionally, water-dispersible silver nanoparticles functionalized with thiophene-substituted pyrogallol[4]arene (Pg 4 THP 4 –AgNPs) were synthesized and characterized by X-ray diffraction, UV–visible spectroscopy, and transmission electron microscopy. The sensing capabilities of Pg 4 THP 4 –AgNPs toward various metal ions were evaluated, revealing high selectivity for Hg 2+ ions, marked by a distinct colorimetric response. Selectivity studies demonstrated that Hg 2+ detection by Pg 4 THP 4 –AgNPs was free of interference from other metal ions. The detection mechanism is based on the displacement of the Pg 4 THP 4 macrocycle from the nanoparticle surface in the presence of Hg 2+, leading to the aggregation of the exposed silver nanoparticles and a resulting optical signal.