A dinitrophenol-based colorimetric chemosensor sequentially sensing Cu²⁺ and S²⁻, HDHT ((E)-2-(2-(2-hydroxy-3,5-dinitrobenzylidene)hydrazineyl)-N,N,N-trimethyl-2-oxoethan-1-aminium), was designed and synthesized. The HDHT selectively detected Cu²⁺ through a color change of yellow to colorless. The calculated detection limit of the HDHT for Cu²⁺ was 6.4 × 10⁻² μM. In the interference test, the HDHT was not considerably inhibited by various metal ions in its detection of Cu²⁺. The chelation ratio of the HDHT to Cu²⁺ was determined as 1:1 by using a Job plot and ESI-MS experiment. In addition, the HDHT–Cu²⁺ complex showed that its color selectively returned to yellow only in the presence of S²⁻. The detection limit of the HDHT–Cu²⁺ complex for S²⁻ was calculated to be 1.2 × 10⁻¹ μM. In the inhibition experiment for S²⁻, the HDHT–Cu²⁺ complex did not significantly interfere with other anions. In the real water-sample test, the detection performance of the HDHT for Cu²⁺ and S²⁻ was successfully examined. The detection features of HDHT for Cu²⁺ and the HDHT–Cu²⁺ for S²⁻ were suggested by the Job plot, UV–Vis, ESI-MS, FT-IR spectroscopy, and DFT calculations.

The first chalcone-based colorimetric chemosensor DPP (sodium (E)-2,4-dichloro-6-(3-oxo-3-(pyridine-2-yl)prop-1-en-1-yl)phenolate) was synthesized for detecting Ni²⁺ in near-perfect water. The synthesis of DPP was validated by using ¹H, ¹³C NMR and ESI-MS. DPP selectively sensed Ni²⁺ through the color variation from yellow to purple. Detection limit of DPP for Ni²⁺ was calculated to be 0.36 μM (3σ/slope), which is below the standard (1.2 μM) set by the United States Environmental Protection Agency (EPA).The binding ratio of DPP to Ni²⁺ was determined as a 1:1 by using a Job plot and ESI-mass. The association constant of DPP and Ni²⁺ was calculated as 1.06 × 10⁴ M⁻¹ by the non-linear fitting analysis. In real samples, the sensing application of DPP for Ni²⁺ was successfully performed. DPP-coated paper-supported strips could also be used for detecting Ni²⁺. The binding mechanism of DPP to Ni²⁺ was proposed by ESI-MS, Job plot, UV-vis, FT-IR spectroscopy, and DFT calculations.