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We designed a rhodamine B‐based colorimetric chemosensor BHSO ((Z)‐3′,6′‐bis(diethylamino)‐2‐(2‐(((8‐hydroxy‐2,3,6,7‐tetrahydro‐1H,5H‐pyrido[3,2,1‐ij]quinolin‐9‐yl)methylene)amino)ethyl)spiro[isoindoline‐1,9′‐xanthen]‐3‐one) for detecting Cu2+. In the presence of Cu2+, BHSO caused a colour variation from colourless to bright orange. The limit of detection for Cu2+ towards BHSO was 0.73 μM. The binding of BHSO to Cu2+ was analysed as a 1:1 ratio through a Job plot and electrospray ionisation mass spectrometry. BHSO can detect readily Cu2+ with a test strip by colorimetric variation. The detecting process of Cu2+ by BHSO was represented by ultraviolet‐visible titration, electrospray ionisation mass spectrometry, proton nuclear magnetic resonance titration, Job plot and density functional theory calculations.

A crown-ether-type colorimetric chemosensor EDDAJ (9,9 0 -((1E,11E)-5,8-dioxa-2,11-diazadodeca-1,11-diene-1,12-diyl)bis (2,3,6,7-tetrahydro-1H,5H-pyrido[3,2,1-ij]quinolin-8-ol) was synthesized. EDDAJ could detect Fe 3+/2+ by a color variation from colorless to dark green in aqueous media. Detection limit of iron ion was 0.43 μM. Complexation ratio of EDDAJ to Fe 3+ was determined to be 1:1 with the results of Job plot and ESI-mass. Based on Job plot, EPR, and ESI-mass experiments, the probing mechanism of EDDAJ to Fe 3+/2+ was demonstrated.

We designed a thiophene-based fluorescent chemosensor DHTCdetecting gallium (Ga 3+ ). DHTC could probe Ga 3+ using fluorescence enhancement.The limit of detection for Ga 3+ by DHTC was 0.39 μM. The binding mode of DHTC to Ga 3+ was determined as a 1:1 ratio from analysis by Job's plot and electrospray ionization-mass spectrometry (ESI-MS). In addition, DHTC could selectively detect Ga 3+ using test kits. The sensing process of Ga 3+ by DHTC was presented using ultraviolet-visible light titration, Job's plot, ESI-MS, 1 H nuclear magnetic resonance titration, and density functional theory calculation.

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