A highly selective silver ion optical chemosensor based on isoxazolyl-azo pyrimidine: synthesis, spectroscopy, DFT...

In this work, an isoxazolyl-azo pyrimidine optical chemosensor (PICS) was efficiently synthesized and applied for naked-eye detection of Ag⁺ ions in solution. The chemical formula of the PICS was recognized by UV-vis, FTIR and NMR analyses. The detection ability of PICS toward various ions was assessed. The results revealed the excellent selectivity and sensitivity of the chemosensor PICS to Ag⁺ ions in aqueous DMSO solutions. The PICS displayed an obvious color change from yellow to dark red in the presence of silver ions. The PICS could efficiently detect Ag⁺ ions over a wide pH range of 6-11, which makes it suitable for detection of Ag⁺ under physiological conditions. PICS also binds Ag⁺ ions to form a 1 : 1 stoichiometry complex (PICS-Ag⁺), resulting in a bathochromic shift in the absorption maximum from 372 to 410 nm. The detection limit of the probe PICS towards Ag⁺ was calculated to be 1.78 μM. Furthermore, the probe PICS shows excellent detection performance in the solid state, and PICS-based test strips were fabricated and applied as efficient Ag⁺ test kits for detection of silver ions in water samples. In addition, the sensing mechanism of PICS-Ag⁺ was completely evaluated using the density functional theory (DFT) calculations. Results indicated that the calculated energy gap between the HOMO and LUMO (3.41 eV) of PICS-Ag is lower than that of the free PICS (3.57 eV). This suggests that a red shift occurred upon addition of the Ag⁺ ion to PICS.