Thiophene-Appended Benzothiazole Compounds for Ratiometric Detection of Copper and Cadmium Ions with Comparative Density Functional Theory Studies and Their Application in Real-Time Samples.

A thirst for the development of a simple fluorescence probe for enhanced sensing application has been achieved by synthesizing a stupendous thiophene-appended benzothiazole-conjugated compound . The synthesized compound was characterized using nuclear magnetic resonance and mass spectrometry techniques. Furthermore, a photophysical property of and reveals the enhanced emission spectrum of because of a restricted spin-orbital coupling as a result of increased conjugation compared to the ligand . Therefore, comparative studies were undertaken for and . Henceforth, was deployed for the ratiometric detection of Cd ions in THF:water and for the detection of Cu ions in THF medium. The chemosensor shows an outstanding water tolerance up to 60% and is stable between pH 2 and 7. This level of water tolerance and stability make a suitable probe for analyzing real-time and biological samples. While the cadmium ion was added to , there was a significant red shift in emission from 496 to 549 nm, which indicates the controlled ICT due to complex formation. The metal-ligand complexation was also confirmed by noticing a decreased band gap of metal complex compared to the ligand as calculated using Tauc's plot with solid-phase UV data. The stoichiometric ratio was obtained by Job's plot that exhibited a 1:1 ratio of and Cd ions, and the limit of detection (LOD) was found to be 2.25 nM by the photoluminescence spectroscopic technique. The fluorescence lifetime of both and was found to be 58.3 ps and 0.147 ns, respectively. Alongside, the colorimetric-assisted ratiometric detection of Cu by with 1:2 stoichiometric ratio having an LOD of 1.06 × 10 M was also performed. Furthermore, the practical applicability of the probe in sensing cadmium was tested in sewage water and vegetable extract; the recovery was approximately 98 and 99%, respectively. The experimental data were supported by theoretical investigation of structures of , , , and , complex formation, charge transfer mechanism, and band gap measurements done by quantum chemical density functional theory calculations.