Ethyl 3-aminobenzo[b]thiophene-2-carboxylate Derived Ratiometric Schiff Base Fluorescent Sensor for the Recognition of In³⁺ and Pb²⁺

An ethyl 3-aminobenzo[b]thiophene-2-carboxylate derived ratiometric Schiff base fluorescent sensor R was devised and synthesized. R exhibited a highly sensitive and selective ratiometric response to In³⁺ in DMF/H₂O tris buffer solution. R exhibited a colorimetric/fluorescent dual-channel response to In³⁺. More importantly, R can distinguish In³⁺ from Ga³⁺ and Al³⁺ in less than 5 min. R exhibited a good linear correlation with the concentration of In³⁺ in the 5–25 μM range and the limit of detection for In³⁺ was found to be 8.36 × 10^–9 M. According to the job`s plot and MS spectra, R formed a complex with In³⁺ at 1:2 with a complexation constant of 8.24 × 10⁹ M². Based on Gaussian theory calculations, the response mechanism of R to In³⁺ can be explained by photo-induced electron transfer (PET) and intramolecular charge transfer (ICT) mechanisms. In addition, R can be used for the detection of indium in tap water with satisfactory recoveries. Meanwhile, R displayed a linear relationship to micromolar concentrations (0-50 μM) of Pb²⁺ and recognized Pb²⁺ in a ratiometric response with a detection limit of 8.3 × 10^–9 M.