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[Display omitted] • Ninhydrin and Isatin-based chromogenic chemosensors selective for Cr3+ and Pb2+ ions were established. • NMR, FTIR, UV–vis and ESI-MS spectroscopy methods were used to confirm the probe and interaction of the probe with the analytes. • Probe L1 and L2 effective sense at colorimetric method was observed to be 2.80 × 10-6 M and 1.63 × 10-6 M detection limits. • Test Strip was designed to monitor the absorbance of Cr3+ and Pb2+ ions in real time analysis. • In a molecular logic circuit, the reversible and reproducible colorimetric switching off L1 and L2 was also discovered. A simple and easily synthesizable chromogenic small molecules probe L4 (2-(2-(benzo[ d ]thiazol-2-yl)hydrazono)-1H-indene-1,3(2H)-dione) and L5 (2-(2-(benzo[ d ]thiazol-2-yl)hydrazono)indolin-3-one) have been synthesized and characterized by various spectroscopy techniques such as FT-IR, NMR, and HRMS. The colorimetric naked eye detection of probe L4 showed a color change towards Cr3+ from orange color to pale yellow, whereas in case of L5 Pb2+ yellow to orange color was witnessed. The jobs plot analyses indicate the 1:1 binding stoichiometric for Cr3+ and 1:2 binding stoichiometric for Pb2+ ions with probes L4 and L5 respectively. The binding association constant (k a) values for L4 and L5 were found to be 6.651 × 10-5 M for Cr3+ and 6.493 × 10-5 M for Pb2+ ions. The limit of detection was found to be for Cr3+ (1.69 × 10−7 M) and Pb2+ (1.208 × 10−7 M) are far below than the limit set by the World Health Organization (WHO) for drinking water. Finally, the designed probes were applied for visible colorimetric test kits and real samples for rapid detection of Cr3+ and Pb2+ for all practical purposes, indicating their potential use in environmental samples. [ABSTRACT FROM AUTHOR]

[Display omitted] • A simple and novel Schiff base that is selective for cupric ions. • NMR, FTIR, and ESI-MS spectroscopy methods were used to confirm the interaction of the probe with the analytes. • Probe R1 effective sense at colorimetric method was observed to be 2.74 × 10-7 M detection limits. • The analysis kit was created to track the use of cupric ions in real-time. A novel sulfonohydrazide Schiff base colorimetric probe 4-methylbenzenesulfonohydrazide (R1) has been designed and synthesized which shows sensing recognition of Cu2+ in CH 3 CN:H 2 O (7:3, v/v) semi-aqueous medium. The prepared probe R1 was characterized using spectroscopic methods, including FT-IR, 1H NMR, and HRMS spectrometry. R1 exhibits an excellent selectivity to Cu2+ over other examined metal ions with a prominent colorimetric performance from colorless (345 nm) to crimson yellow (420 nm) under daylight. UV–vis titration experiment in the presence of different molar fractions of Cu2+ was used to perform a Job's plot analysis. The results showed that the stoichiometric ratio of the complex formed by R1 and Cu2+ was 2:1. A paper strip pre-stained with R1 solution was further fabricated and it also showed excellent sensing ability toward Cu2+ with a detection limit as low as 2.74 × 10-7 M with the naked eye, which represents better portability and operation simplicity that is favourable for on-site analysis of Cu2+ in water. The sensing mechanism was further verified with HOMO–LUMO energy levels were calculated using experimental and theoretical studies (DFT/TD-DFT), which correlated with good agreement. [ABSTRACT FROM AUTHOR]

[Display omitted] • Benzohydrazide-based chromogenic chemosensors for Hg2+ ion is established. • NMR, FTIR, UV–Vis and HRMS methods were used to confirm the ligand and complex. • PN effective sensing with Hg2+ ions were observed to be 3.08 × 10−7 M detection limit. • Test strip was designed to monitor the absorbance of Hg2+ ions in real time analysis. Metal ions play a crucial role in serving the proper functioning of living beings. Whereas Hg2+ ions are non-essential and toxic even at a minute level for living organisms. Thus, a simple colorimetric approach for Hg2+ ion detection is used. In this work, the synthesis of novel benzohydrazide-based Schiff base ligand (PN) as a sensor and exploring its colorimetric recognition ability. The ligand PN has been designed and synthesized via an economical and simple one-step condensation process. The as-synthesized PN ligand were successfully characterized by various spectroscopic techniques like 1H NMR, 13C NMR, FT-IR, HRMS and ICP-OES. ligand PN manifest outstanding selectivity for Hg2+ ions leaving the rest of the examined metal ions in mixed aqueous medium. A colour change of colourless to crimson yellow is prominent under UV light. The Job plot has shown formation of complex of 1:1 stoichiometric ratio of PN and Hg2+ ions; which is produced by conducting UV–vis titrations using different molar fractions of Hg2+ ions. Moreover, theoretical DFT calculations are validated by experimental data. Furthermore, pre-stained paper strips are furnished and it also showed excellent instantaneous Hg2+ naked eye sensing with a limit of detection as low as 3.08 × 10−7 M. [ABSTRACT FROM AUTHOR]