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.

A naphthol and nitro‐aniline‐based fluorometric and colorimetric chemosensor BHMN, 1,1‐bis(2‐(((E)‐(2‐hydroxy naphthalene‐1‐yl)methylene)amino)ethyl)‐3‐(4‐nitrophenyl)thiourea, was synthesized. Sensor BHMN detected Al3+ with fluorescence turn‐on and Fe3+ via color variation of colorless to purple. Binding ratios of BHMN to Al3+ and Fe3+ turned out to be 1 : 1. Detection limits for Al3+ and Fe3+ by BHMN were analyzed to be 8.22 μM and 3.10 μM. Additionally, the naked‐eye test strip was applied for sensing Fe3+ and showed that BHMN could effectively discriminate Fe3+ from Fe2+ and other cations. The binding mechanisms of BHMN to Al3+ and Fe3+ were identified by ESI‐mass, Job plot, NMR titration, and DFT calculations.

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