Colorimetric Metal Sensing of Fe3+ and Cr3+ and Photophysical and Electrochemical Studies Based on Benzo[4,5]thiazolo[3,2-a]pyrimidine-3-carboxylate and Its Derivatives

Benzo[4,5]thiazolo[3, 2-a]pyrimidine-3-carboxylate derivatives (4a–i) containing electron-donor and electron-acceptor groups with remarkable photophysical and electrochemical properties were synthesized. The changes in absorption properties of compound 4a in the presence of various cations were evaluated. Compound 4a can act as a colorimetric sensor for highly sensitive and selective detection of Fe3+ and Cr3+in acetonitrile solvent. Using measurements of absorbance intensity, the binding constants for the 4a + Fe3+ complex and 4a + Cr3+ complex were found to be 1.958 × 108 and 1.5442 × 107 M–1 with lower detection limits of 52 and 110 nM, respectively. 1H NMR titrations, Fourier transform infrared (FTIR) studies, electrospray ionization (ESI)-mass spectra, and Job's plots were used to verify the mechanism of the specific reaction and colorimetric sensing of 4a + Fe3+ and 4a + Cr3+. The application of compound 4a for the determination of Fe3+ in spiked samples of iron tablets in different environmental water samples showed a satisfactory result with good recovery.