Structure analysis and evaluation of two probes for the colorimetric detection of Hg2+ and turn-on fluorescence-based detection of Cd2+ ions in an aqueous solution

Abstract

Synthetic molecular probes with fluorescent and colorimetric signals are valuable tools for the detection of toxic metal ions. Therefore, two synthetic molecular probes based on quinoline moiety were prepared by substituting it with a sulfonate group and piperidine or morpholine moieties. Quinoline integrated probes were characterized via 1H, 13C-NMR, and single-crystal X-ray crystallography techniques. The structures were further investigated using the crystal explorer program. The intermolecular interactions were quantitatively explored using Hirshfeld surface analysis and 2-D fingerprint plots. The strength of intermolecular interactions was further investigated using the TONTO program at the B3LYP/6-31(d,p) level of theory. The integrated receptors were capable of selectively detecting Hg2+ and Cd2+ ions in aqueous media using UV-Visible and fluorescence spectroscopy, respectively. The structural design of the probe was such that it could selectively signal the presence of the metal ions. The receptors produced enhanced fluorescence intensity in the presence of Cd2+ ions, while no fluorescence emission was observed for Hg2+ ions. The computational study based on M062X/6-31+G(d)-LANL2TZ was used to further investigate the structure of the molecular probe and their complexes.